Signalling Connection Control Part User Adaptation Layer (SUA)
RFC 3868
| Document | Type | RFC - Proposed Standard (October 2004) IPR | |
|---|---|---|---|
| Authors | Gery Verwimp, Brian Bidulock , Joe Keller , Greg Sidebottom , Lode Coene , John A. Loughney | ||
| Last updated | 2015-10-14 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| IESG | Responsible AD | Jon Peterson | |
| Send notices to | (None) |
RFC 3868
Network Working Group A. Atlas
Internet-Draft Juniper Networks
Intended status: Informational J. Halpern
Expires: December 25, 2014 Ericsson
S. Hares
Hickory Hill Consulting
D. Ward
Cisco Systems
T. Nadeau
Brocade
June 23, 2014
An Architecture for the Interface to the Routing System
draft-ietf-i2rs-architecture-04
Abstract
This document describes an architecture for a standard, programmatic
interface for state transfer in and out of the internet routing
system. It describes the basic architecture, the components, and
their interfaces with particular focus on those to be standardized as
part of I2RS.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 25, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
Atlas, et al. Expires December 25, 2014 [Page 1]
Internet-Draft I2RS Arch June 2014
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Drivers for the I2RS Architecture . . . . . . . . . . . . 4
1.2. Architectural Overview . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9
3. Key Architectural Properties . . . . . . . . . . . . . . . . 10
3.1. Simplicity . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Extensibility . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Model-Driven Programmatic Interfaces . . . . . . . . . . 11
4. Security Considerations . . . . . . . . . . . . . . . . . . . 12
4.1. Identity and Authentication . . . . . . . . . . . . . . . 13
4.2. Authorization . . . . . . . . . . . . . . . . . . . . . . 13
5. Network Applications and I2RS Client . . . . . . . . . . . . 14
5.1. Example Network Application: Topology Manager . . . . . . 15
6. I2RS Agent Role and Functionality . . . . . . . . . . . . . . 15
6.1. Relationship to its Routing Element . . . . . . . . . . . 15
6.2. I2RS State Storage . . . . . . . . . . . . . . . . . . . 16
6.2.1. I2RS Agent Failure . . . . . . . . . . . . . . . . . 16
6.2.2. Starting and Ending . . . . . . . . . . . . . . . . . 17
6.2.3. Reversion . . . . . . . . . . . . . . . . . . . . . . 17
6.3. Interactions with Local Config . . . . . . . . . . . . . 17
6.4. Routing Components and Associated I2RS Services . . . . . 18
6.4.1. Routing and Label Information Bases . . . . . . . . . 19
6.4.2. IGPs, BGP and Multicast Protocols . . . . . . . . . . 20
6.4.3. MPLS . . . . . . . . . . . . . . . . . . . . . . . . 20
6.4.4. Policy and QoS Mechanisms . . . . . . . . . . . . . . 21
6.4.5. Information Modeling, Device Variation, and
Information Relationships . . . . . . . . . . . . . . 21
6.4.5.1. Managing Variation: Object Classes/Types and
Inheritance . . . . . . . . . . . . . . . . . . . 21
6.4.5.2. Managing Variation: Optionality . . . . . . . . . 22
6.4.5.3. Managing Variation: Templating . . . . . . . . . 22
6.4.5.4. Object Relationships . . . . . . . . . . . . . . 23
6.4.5.4.1. Initialization . . . . . . . . . . . . . . . 23
6.4.5.4.2. Correlation Identification . . . . . . . . . 23
6.4.5.4.3. Object References . . . . . . . . . . . . . . 24
6.4.5.4.4. Active Reference . . . . . . . . . . . . . . 24
7. I2RS Client Agent Interface . . . . . . . . . . . . . . . . . 24
7.1. One Control and Data Exchange Protocol . . . . . . . . . 24
Atlas, et al. Expires December 25, 2014 [Page 2]
Internet-Draft I2RS Arch June 2014quot;) MAY be sent to all
inactive ASPs, if required. An ASP Inactive Ack message is sent to
the ASP after all traffic is halted and Layer Management is informed
with an M-ASP_INACTIVE indication primitive.
Multiple ASP Inactive Ack messages MAY be used in response to an ASP
Inactive message containing multiple Routing Contexts, allowing the
SGP or IPSP to independently acknowledge for different (sets of)
Routing Contexts. The SGP or IPSP sends an Error message ("Invalid
Routing Context") message for each invalid or not configured Routing
Context value in a received ASP Inactive message.
The SGP MUST send an ASP Inactive Ack message in response to a
received ASP Inactive message from the ASP and the ASP is already
marked as ASP-INACTIVE at the SGP.
At the ASP, the ASP Inactive Ack message received is not
acknowledged. Layer Management is informed with an M-ASP_INACTIVE
confirm primitive. If the ASP receives an ASP Inactive Ack without
having sent an ASP Inactive message, the ASP should now consider
itself as in the ASP-INACTIVE state. If the ASP was previously in
the ASP-ACTIVE state, the ASP should then initiate procedures to
return itself to its previous state. When the ASP sends an ASP
Inactive message it starts timer T(ack). If the ASP does not receive
a response to an ASP Inactive message within T(ack), the ASP MAY
restart T(ack) and resend ASP Inactive messages until it receives an
ASP Inactive Ack message. T(ack) is provisioned, with a default of 2
seconds. Alternatively, retransmission of ASP Inactive messages MAY
be put under control of Layer Management. In this method, expiry of
T(ack) results in a M-ASP_Inactive confirm primitive carrying a
negative indication.
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RFC 3868 SUA October 2004
If no other ASPs in the Application Server are in the state ASP-
ACTIVE, the SGP MUST send a Notify message ("AS-Pending") to all of
the ASPs in the AS which are in the state ASP-INACTIVE. The SGP
SHOULD start buffering the incoming messages for T(r) seconds, after
which messages MAY be discarded. T(r) is configurable by the network
operator. If the SGP receives an ASP Active message from an ASP in
the AS before expiry of T(r), the buffered traffic is directed to
that ASP and the timer is cancelled. If T(r) expires, the AS is
moved to the AS-INACTIVE state.
4.3.4.4.1. IPSP Considerations
An IPSP may be considered in the ASP-INACTIVE state by a remote IPSP
after an ASP Inactive or ASP Inactive Ack message has been received
from it.
Alternatively, when using IPSP DE model, an interchange of ASP
Inactive messages from each end MUST be performed. Four messages are
needed for completion.
4.3.4.5. Notify Procedures
A Notify message reflecting a change in the AS state MUST be sent to
all ASPs in the AS, except those in the ASP-DOWN state, with
appropriate Status Information and any ASP Identifier of the failed
ASP. At the ASP, Layer Management is informed with an M-NOTIFY
indication primitive. The Notify message must be sent whether the AS
state change was a result of an ASP failure or reception of an ASP
State management (ASPSM) / ASP Traffic Management (ASPTM) message.
In the second case, the Notify message MUST be sent after any ASP
State or Traffic Management related acknowledgement messages (e.g.,
ASP Up Ack, ASP Down Ack, ASP Active Ack, or ASP Inactive Ack).
In the case where a Notify ("AS-PENDING") message is sent by an SGP
that now has no ASPs active to service the traffic, or where a Notify
("Insufficient ASP resources active in AS") message MUST be sent in
the Loadshare or Broadcast mode, the Notify message does not
explicitly compel the ASP(s) receiving the message to become active.
The ASPs remain in control of what (and when) traffic action is
taken.
In the case where a Notify message does not contain a Routing Context
parameter, the receiver must know, via configuration data, of which
Application Servers the ASP is a member and take the appropriate
action in each AS.
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4.3.4.5.1. IPSP Considerations (NTFY)
Notify works in the same manner as in the SG-AS case. One of the
IPSPs can send this message to any remote IPSP that is not in the
ASP-DOWN state.
4.3.4.6. Heartbeat Procedures
The optional Heartbeat procedures MAY be used when operating over
transport layers that do not have their own heartbeat mechanism for
detecting loss of the transport association (i.e., other than SCTP).
Either SUA peer may optionally send Heartbeat messages periodically,
subject to a provisioned timer T(beat). Upon receiving a Heartbeat
message, the SUA peer MUST respond with a Heartbeat Ack message.
If no Heartbeat Ack message (or any other SUA message) is received
from the SUA peer within 2*T(beat), the remote SUA peer is considered
unavailable. Transmission of Heartbeat messages is stopped and the
signalling process SHOULD attempt to reestablish communication if it
is configured as the client for the disconnected SUA peer.
The Heartbeat message may optionally contain an opaque Heartbeat Data
parameter that MUST be echoed back unchanged in the related Heartbeat
Ack message. The sender, upon examining the contents of the returned
Heartbeat Ack message, MAY choose to consider the remote SUA peer as
unavailable. The contents/format of the Heartbeat Data parameter is
implementation-dependent and only of local interest to the original
sender. The contents may be used, for example, to support a
Heartbeat sequence algorithm (to detect missing Heartbeats), and/or a
timestamp mechanism (to evaluate delays).
Note: Heartbeat related events are not shown in Figure 2 "ASP state
transition diagram".
4.4. Routing Key Management Procedures
4.4.1. Registration
An ASP MAY dynamically register with an SGP as an ASP within an
Application Server using the REG REQ message. A Routing Key
parameter in the REG REQ message specifies the parameters associated
with the Routing Key.
The SGP examines the contents of the received Routing Key parameter
and compares it with the currently provisioned Routing Keys. If the
received Routing Key matches an existing SGP Routing Key entry, and
the ASP is not currently included in the list of ASPs for the related
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RFC 3868 SUA October 2004
Application Server, the SGP MAY authorize the ASP to be added to the
AS. Or, if the Routing Key does not currently exist and the received
Routing Key data is valid and unique, an SGP supporting dynamic
configuration MAY authorize the creation of a new Routing Key and
related Application Server and add the ASP to the new AS. In either
case, the SGP returns a Registration Response message to the ASP,
containing the same Local-RK-Identifier as provided in the initial
request, and a Registration Result "Successfully Registered". A
unique Routing Context value assigned to the SGP Routing Key is
included. The method of Routing Context value assignment at the SGP
is implementation dependent but must be guaranteed to be unique for
each Application Server or Routing Key supported by the SGP. If the
SGP determines that the received Routing Key data is invalid, or
contains invalid parameter values, the SGP returns a Registration
Response message to the ASP, containing a Registration Result "Error
- Invalid Routing Key", "Error - Invalid DPC", "Error - Invalid
Network Appearance" as appropriate.
If the SGP does not support the registration procedure, the SGP
returns an Error message to the ASP, with an error code of
"Unsupported Message Type".
If the SGP determines that a unique Routing Key cannot be created,
the SGP returns a Registration Response message to the ASP, with a
Registration Status of "Error - Cannot Support Unique Routing". An
incoming signalling message received at an SGP should not match
against more than one Routing Key.
If the SGP does not authorize the registration request, the SGP
returns a REG RSP message to the ASP containing the Registration
Result "Error - Permission Denied".
If an SGP determines that a received Routing Key does not currently
exist and the SGP does not support dynamic configuration, the SGP
returns a Registration Response message to the ASP, containing a
Registration Result "Error - Routing Key not Currently Provisioned".
If an SGP determines that a received Routing Key does not currently
exist and the SGP supports dynamic configuration but does not have
the capacity to add new Routing Key and Application Server entries,
the SGP returns a Registration Response message to the ASP,
containing a Registration Result "Error - Insufficient Resources".
If an SGP determines that one or more of the Routing Key parameters
are not supported for the purpose of creating new Routing Key
entries, the SGP returns a Registration Response message to the ASP,
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RFC 3868 SUA October 2004
containing a Registration Result "Error - Unsupported RK parameter
field". This result MAY be used if, for example, the SGP does not
support RK Address parameter.
A Registration Response "Error - Unsupported Traffic Handling Mode"
is returned if the Routing Key in the REG REQ contains a Traffic
Handling Mode that is inconsistent with the presently configured mode
for the matching Application Server.
An ASP MAY register multiple Routing Keys at once by including a
number of Routing Key parameters in a single REG REQ message. The
SGP MAY respond to each registration request in a single REG RSP
message, indicating the success or failure result for each Routing
Key in a separate Registration Result parameter. Alternatively the
SGP MAY respond with multiple REG RSP messages, each with one or more
Registration Result parameters. The ASP uses the Local-RK-Identifier
parameter to correlate the requests with the responses.
An ASP MAY modify an existing Routing Key by including a Routing
Context parameter in the REG REQ. If the SGP determines that the
Routing Context applies to an existing Routing Key, the SG MAY adjust
the existing Routing Key to match the new information provided in the
Routing Key parameter. A Registration Response "Routing Key Change
Refused" is returned if the SGP does not accept the modification of
the Routing Key.
Upon successful registration of an ASP in an AS, the SGP can now send
related SS7 Signalling Network Management messaging, if this did not
previously start upon the ASP transitioning to state ASP-INACTIVE.
4.4.2. Deregistration
An ASP MAY dynamically deregister with an SGP as an ASP within an
Application Server using the DEREG REQ message. A Routing Context
parameter in the DEREG REQ message specifies which Routing Keys to
deregister. An ASP SHOULD move to the ASP-INACTIVE state for an
Application Server before attempting to deregister the Routing Key
(i.e., deregister after receiving an ASP Inactive Ack). Also, an ASP
SHOULD deregister from all Application Servers that it is a member
before attempting to move to the ASP-Down state.
The SGP examines the contents of the received Routing Context
parameter and validates that the ASP is currently registered in the
Application Server(s) related to the included Routing Context(s). If
validated, the ASP is deregistered as an ASP in the related
Application Server.
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The deregistration procedure does not necessarily imply the deletion
of Routing Key and Application Server configuration data at the SGP.
Other ASPs may continue to be associated with the Application Server,
in which case the Routing Key data SHOULD NOT be deleted. If a
Deregistration results in no more ASPs in an Application Server, an
SGP MAY delete the Routing Key data.
The SGP acknowledges the deregistration request by returning a DEREG
RSP message to the requesting ASP. The result of the deregistration
is found in the Deregistration Result parameter, indicating success
or failure with cause.
An ASP MAY deregister multiple Routing Contexts at once by including
a number of Routing Contexts in a single DEREG REQ message. The SGP
MAY respond to each deregistration request in a single DEREG RSP
message, indicating the success or failure result for each Routing
Context in a separate Deregistration Result parameter.
4.4.3. IPSP Considerations (REG/DEREG)
The Registration/Deregistration procedures work in the IPSP cases in
the same way as in AS-SG cases. An IPSP may register an RK in the
remote IPSP. An IPSP is responsible for deregistering the RKs that
it has registered.
4.5. Availability and/or Congestion Status of SS7 Destination Support
4.5.1. At an SGP
On receiving a N-STATE, N-PCSTATE and N-INFORM indication primitive
from the nodal interworking function at an SGP, the SGP SUA layer
will send a corresponding SS7 Signalling Network Management (SNM)
DUNA, DAVA, SCON, or DUPU message (see Section 3.4) to the SUA peers
at concerned ASPs. The SUA layer must fill in various fields of the
SNM messages consistently with the information received in the
primitives.
The SGP SUA layer determines the set of concerned ASPs to be informed
based on the specific SS7 network for which the primitive indication
is relevant. In this way, all ASPs configured to send/receive
traffic within a particular network appearance are informed. If the
SGP operates within a single SS7 network appearance, then all ASPs
are informed.
DUNA, DAVA, SCON, and DRST messages are sent sequentially and
processed at the receiver in the order sent. SCTP stream 0 SHOULD
NOT be used. The Unordered bit in the SCTP DATA chunk MAY be used
for the SCON message.
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Sequencing is not required for the DUPU or DAUD messages, which MAY
be sent unordered. SCTP stream 0 is used, with optional use of the
Unordered bit in the SCTP DATA chunk.
4.5.2. At an ASP
4.5.2.1. Single SG Configurations
At an ASP, upon receiving an SS7 Signalling Network Management (SSNM)
message from the remote SUA Peer, the SUA layer invokes the
appropriate primitive indications to the resident SUA-Users. Local
management is informed.
In the case where a local event has caused the unavailability or
congestion status of SS7 destinations, the SUA layer at the ASP
SHOULD pass up appropriate indications in the primitives to the SUA
User, as though equivalent SSNM messages were received. For example,
the loss of an SCTP association to an SGP may cause the
unavailability of a set of SS7 destinations. N-PCSTATE indication
primitives to the SUA User are appropriate.
Implementation Note: To accomplish this, the SUA layer at an ASP
maintains the status of routes via the SG.
4.5.2.2. Multiple SG Configurations
At an ASP, upon receiving a Signalling Network Management message
from the remote SUA Peer, the SUA layer updates the status of the
affected route(s) via the originating SG and determines, whether or
not the overall availability or congestion status of the effected
destination(s) has changed. If so, the SUA layer invokes the
appropriate primitive indications to the resident SUA-Users. Local
management is informed.
4.5.3. ASP Auditing
An ASP may optionally initiate an audit procedure to inquire of an
SGP the availability and, if the national congestion method with
multiple congestion levels and message priorities is used, congestion
status of an SS7 destination or set of destinations. A Destination
Audit (DAUD) message is sent from the ASP to the SGP requesting the
current availability and congestion status of one or more SS7
destinations or subsystems.
The DAUD message MAY be sent unordered. The ASP MAY send the DAUD in
the following cases:
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- Periodic. A Timer originally set upon reception of a DUNA, SCON or
DRST message has expired without a subsequent DAVA,
DUNA, SCON or DRST message updating the
availability/congestion status of the affected
Destination Point Code. The Timer is reset upon issuing
a DAUD. In this case the DAUD is sent to the SGP that
originally sent the SSNM message.
- Isolation. The ASP is newly ASP-ACTIVE or has been isolated from an
SGP for an extended period. The ASP MAY request the
availability/congestion status of one or more SS7
destinations to which it expects to communicate.
Implementation Note:
In the first of the cases above, the auditing procedure must not
be invoked for the case of a received SCON message containing a
congestion level value of "no congestion" or undefined" (i.e.,
congestion Level = "0"). This is because the value indicates
either congestion abatement or that the ITU MTP3 international
congestion method is being used. In the international congestion
method, the MTP3 layer at the SGP does not maintain the congestion
status of any destinations and therefore the SGP cannot provide
any congestion information in response to the DAUD. For the same
reason, in the second of the cases above a DAUD message cannot
reveal any congested destination(s).
The SGP SHOULD respond to a DAUD message with the availability and
congestion status of the subsystem. The status of each SS7
destination or subsystem requested is indicated in a DUNA message (if
unavailable), a DAVA message (if available), or a DRST (if restricted
and the SGP supports this feature). If the SS7 destination or
subsystem is available and congested, the SGP responds with an SCON
message in addition to the DAVA message. If the SS7 destination or
subsystem is restricted and congested, the SGP responds with an SCON
message in addition to the DRST. If the SGP has no information on
the availability / congestion status of the SS7 destination or
subsystem, the SGP responds with a DUNA message, as it has no routing
information to allow it to route traffic to this destination or
subsystem.
An SG MAY refuse to provide the availability or congestion status of
a destination or subsystem if, for example, the ASP is not authorized
to know the status of the destination or subsystem. The SG MAY
respond with an Error Message (Error Code = "Destination Status
Unknown") or Error Message (Error Code = "Subsystem Status Unknown").
Loughney, et al. Standards Track [Page 114]
7.2. Communication Channels . . . . . . . . . . . . . . . . . 24
7.3. Capability Negotiation . . . . . . . . . . . . . . . . . 25
7.4. Identity and Security Role . . . . . . . . . . . . . . . 25
7.4.1. Client Redundancy . . . . . . . . . . . . . . . . . . 26
7.5. Connectivity . . . . . . . . . . . . . . . . . . . . . . 26
7.6. Notifications . . . . . . . . . . . . . . . . . . . . . . 27
7.7. Information collection . . . . . . . . . . . . . . . . . 27
7.8. Multi-Headed Control . . . . . . . . . . . . . . . . . . 28
7.9. Transactions . . . . . . . . . . . . . . . . . . . . . . 28
8. Operational and Manageability Considerations . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
11. Informative References . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
Routers that form the internet routing infrastructure maintain state
at various layers of detail and function. For example, a typical
router maintains a Routing Information Base (RIB), and implements
routing protocols such as OSPF, ISIS, and BGP to exchange protocol
state and other information about the state of the network with other
routers.
Routers convert all of this information into forwarding entries which
are then used to forward packets and flows between network elements.
The forwarding plane and the specified forwarding entries then
contain active state information that describes the expected and
observed operational behavior of the router and which is also needed
by the network applications. Network-oriented applications require
easy access to this information to learn the network topology, to
verify that programmed state is installed in the forwarding plane, to
measure the behavior of various flows, routes or forwarding entries,
as well as to understand the configured and active states of the
router.
This document sets out an architecture for a common, standards-based
interface to this information. This Interface to the Routing System
(I2RS) facilitates control and observation of the routing-related
state (for example, a Routing Element RIB manager's state), as well
as enabling network-oriented applications to be built on top of
today's routed networks. The I2RS is a programmatic asynchronous
interface for transferring state into and out of the internet routing
system. This I2RS architecture recognizes that the routing system
and a router's OS provide useful mechanisms that applications could
harness to accomplish application-level goals.
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Fundamental to the I2RS are clear data models that define the
semantics of the information that can be written and read. The I2RS
provides a framework for registering for and requesting the
appropriate information for each particular application. The I2RS
provides a way for applications to customize network behavior while
leveraging the existing routing system as desired.
Although the I2RS architecture is general enough to support
information and data models for a variety of data, and aspects of the
I2RS solution may be useful in domain other than routing, I2RS and
this document are specifically focused on an interface for routing
data.
1.1. Drivers for the I2RS Architecture
There are four key drivers that shape the I2RS architecture. First
is the need for an interface that is programmatic, asynchronous, and
offers fast, interactive access for atomic operations. Second is the
access to structured information and state that is frequently not
directly configurable or modeled in existing implementations or
configuration protocols. Third is the ability to subscribe to
structured, filterable event notifications from the router. Fourth,
the operation of I2RS is to be data-model driven to facilitate
extensibility and provide standard data-models to be used by network
applications.
I2RS is described as an asynchronous programmatic interface, the key
properties of which are described in Section 5 of
[I-D.ietf-i2rs-problem-statement].
The I2RS architecture facilitates obtaining information from the
router. The I2RS architecture provides the ability to not only read
specific information, but also to subscribe to targeted information
streams and filtered and thresholded events.
Such an interface also facilitates the injection of ephemeral state
into the routing system. A non-routing protocol or application could
inject state into a routing element via the state-insertion
functionality of the I2RS and that state could then be distributed in
a routing or signaling protocol and/or be used locally (e.g. to
program the co-located forwarding plane). I2RS will only permit
modification of state that would be safe, conceptually, to modify via
local configuration; no direct manipulation of protocol-internal
dynamically determined data is envisioned.
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1.2. Architectural Overview
Figure 1 shows the basic architecture for I2RS between applications
using I2RS, their associated I2RS Clients, and I2RS Agents.
Applications access I2RS services through I2RS clients. A single
client can provide access to one or more applications. In the
figure, Clients A and B provide access to a single application, while
Client P provides access to multiple applications.
Applications can access I2RS services through local or remote
clients. In the figure, Applicatons A and B access I2RS services
through local clients, while Applications C, D and E access I2RS
services through a remote client. The details of how applications
communicate with a remote client is out of scope for I2RS.
An I2RS Client can access one or more I2RS agents. In the figure,
Clients B and P access I2RS Agents 1 and 2. Likewise, an I2RS Agent
can provide service to one or more clients. In the figure, I2RS
Agent 1 provides services to Clients A, B and P while Agent 2
provides services to only Clients B and P.
I2RS agents and clients communicate with one another using an
asynchronous protocol. Therefore, a single client can post multiple
simultaneous requests, either to a single agent or to multiple
agents. Furthermore, an agent can process multiple requests, either
from a single client or from multiple clients, simultaneously.
The I2RS agent provides read and write access to selected data on the
routing element that are organized into I2RS Services. Section 4
describes how access is mediated by authentication and access control
mechanisms. In addition to read and write access, the I2RS agent
allows clients to subscribe to different types of notifications about
events affecting different object instances. An example not related
to the creation, modification or deletion of an object instance is
when a next-hop in the RIB is resolved enough to be used or when a
particular route is selected by the RIB Manager for installation into
the forwarding plane. Please see Section 7.6 and Section 7.7 for
details.
The scope of I2RS is to define the interactions between the I2RS
agent and the I2RS client and the associated proper behavior of the
I2RS agent and I2RS client.
****************** ***************** *****************
* Application C * * Application D * * Application E *
****************** ***************** *****************
^ ^ ^
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| | |
|--------------| | |--------------|
| | |
v v v
***************
* Client P *
***************
^ ^
| |-------------------------|
*********************** | *********************** |
* Application A * | * Application B * |
* * | * * |
* +----------------+ * | * +----------------+ * |
* | Client A | * | * | Client B | * |
* +----------------+ * | * +----------------+ * |
******* ^ ************* | ***** ^ ****** ^ ****** |
| | | | |
| |-------------| | | |-----|
| | -----------------------| | |
| | | | |
************ v * v * v ********* ***************** v * v ********
* +---------------------+ * * +---------------------+ *
* | Agent 1 | * * | Agent 2 | *
* +---------------------+ * * +---------------------+ *
* ^ ^ ^ ^ * * ^ ^ ^ ^ *
* | | | | * * | | | | *
* v | | v * * v | | v *
* +---------+ | | +--------+ * * +---------+ | | +--------+ *
* | Routing | | | | Local | * * | Routing | | | | Local | *
* | and | | | | Config | * * | and | | | | Config | *
* |Signaling| | | +--------+ * * |Signaling| | | +--------+ *
* +---------+ | | ^ * * +---------+ | | ^ *
* ^ | | | * * ^ | | | *
* | |----| | | * * | |----| | | *
* v | v v * * v | v v *
* +----------+ +------------+ * * +----------+ +------------+ *
* | Dynamic | | Static | * * | Dynamic | | Static | *
* | System | | System | * * | System | | System | *
* | State | | State | * * | State | | State | *
* +----------+ +------------+ * * +----------+ +------------+ *
* * * *
* Routing Element 1 * * Routing Element 2 *
******************************** ********************************
Figure 1: Architecture of I2RS clients and agents
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Routing Element: A Routing Element implements some subset of the
routing system. It does not need to have a forwarding plane
associated with it. Examples of Routing Elements can include:
* A router with a forwarding plane and RIB Manager that runs
ISIS, OSPF, BGP, PIM, etc.,
* A BGP speaker acting as a Route Reflector,
* An LSR that implements RSVP-TE, OSPF-TE, and PCEP and has a
forwarding plane and associated RIB Manager,
* A server that runs ISIS, OSPF, BGP and uses ForCES to control a
remote forwarding plane,
A Routing Element may be locally managed, whether via CLI, SNMP,
or NETCONF.
Routing and Signaling: This block represents that portion of the
Routing Element that implements part of the internet routing
system. It includes not merely standardized protocols (i.e. IS-
IS, OSPF, BGP, PIM, RSVP-TE, LDP, etc.), but also the RIB Manager
layer.
Local Config: A Routing Element will provide the ability to
configure and manage it. The Local Config may be provided via a
combination of CLI, NETCONF, SNMP, etc. The black box behavior
for interactions between the state that I2RS installs into the
routing element and the Local Config must be defined.
Dynamic System State: An I2RS agent needs access to state on a
routing element beyond what is contained in the routing subsystem.
Such state may include various counters, statistics, flow data,
and local events. This is the subset of operational state that is
needed by network applications based on I2RS that is not contained
in the routing and signaling information. How this information is
provided to the I2RS agent is out of scope, but the standardized
information and data models for what is exposed are part of I2RS.
Static System State: An I2RS agent needs access to static state on
a routing element beyond what is contained in the routing
subsystem. An example of such state is specifying queueing
behavior for an interface or traffic. How the I2RS agent modifies
or obtains this information is out of scope, but the standardized
information and data models for what is exposed are part of I2RS.
I2RS Agent: See the definition in Section 2.
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Application: A network application that needs to observe the
network or manipulate the network to achieve its service
requirements.
I2RS Client: See the definition in Section 2.
As can be seen in Figure 1, an I2RS client can communicate with
multiple I2RS agents. An I2RS client may connect to one or more I2RS
agents based upon its needs. Similarly, an I2RS agent may
communicate with multiple I2RS clients - whether to respond to their
requests, to send notifications, etc. Timely notifications are
critical so that several simultaneously operating applications have
up-to-date information on the state of the network.
As can also be seen in Figure 1, an I2RS Agent may communicate with
multiple clients. Each client may send the agent a variety of write
operations. In order to keep the protocol simple, two clients should
not attempt to write (modify) the same piece of information on an
I2RS Agent. This is considered an error. However, such collisions
may happen and section 7.8 (multi-headed control) describes how the
I2RS agent resolves collision by first utilizing priority to resolve
collisions, and second by servicing the requests in a first in, first
served basis. The i2rs architecture includes this definition of
behavior for this case simply for predictability not because this is
an intended result. This predictability will simplify the error
handling and suppress oscillations. If additional error cases beyond
this simple treatment are required, these these error cases should be
resolved by the network applications and management systems.
In contrast, although multiple I2RS clients may need to supply data
into the same list (e.g. a prefix or filter list), this is not
considered an error and must be correctly handled. The nuances so
that writers do not normally collide should be handled in the
information models.
The architectural goal for the I2RS is that such errors should
produce predictable behaviors, and be reportable to interested
clients. The details of the associated policy is discussed in
Section 7.8. The same policy mechanism (simple priority per I2RS
client) applies to interactions between the I2RS agent and the
CLI/SNMP/NETCONF as described in Section 6.3.
In addition it must be noted that there may be indirect interactions
between write operations. A basic example of this is when two
different but overlapping prefixes are written with different
forwarding behavior. Detection and avoidance of such interactions is
outside the scope of the I2RS work and is left to agent design and
implementation.
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2. Terminology
The following terminology is used in this document.
agent or I2RS Agent: An I2RS agent provides the supported I2RS
services from the local system's routing sub-systems by
interacting with the routing element to provide specified
behavior. The I2RS agent understands the I2RS protocol and can be
contacted by I2RS clients.
client or I2RS Client: A client implements the I2RS protocol, uses
it to communicate with I2RS Agents, and uses the I2RS services to
accomplish a task. It interacts with other elements of the
policy, provisioning, and configuration system by means outside of
the scope of the I2RS effort. It interacts with the I2RS agents
to collect information from the routing and forwarding system.
Based on the information and the policy oriented interactions, the
I2RS client may also interact with I2RS agents to modify the state
of their associated routing systems to achieve operational goals.
An I2RS client can be seen as the part of an application that uses
and supports I2RS and could be a software library.
service or I2RS Service: For the purposes of I2RS, a service refers
to a set of related state access functions together with the
policies that control their usage. The expectation is that a
service will be represented by a data-model. For instance, 'RIB
service' could be an example of a service that gives access to
state held in a device's RIB.
read scope: The set of information which the I2RS client is
authorized to read. The read scope specifies the access
restrictions to both see the existence of data and read the value
of that data.
notification scope: The set of events and associated information
that the I2RS Client can request be pushed by the I2RS Agent.
I2RS Clients have the ability to register for specific events and
information streams, but must be constrained by the access
restrictions associated with their notification scope.
write scope: The set of field values which the I2RS client is
authorized to write (i.e. add, modify or delete). This access can
restrict what data can be modified or created, and what specific
value sets and ranges can be installed.
scope: When unspecified as either read scope, write scope, or
notification scope, the term scope applies to the read scope,
write scope, and notification scope.
RFC 3868 SUA October 2004
4.6. MTP3 Restart
In the case where the MTP3 in the SG undergoes an MTP restart, event
communication SHOULD be handled as follows:
When the SG discovers SS7 network isolation, the SGPs send an
indication to all concerned available ASPs (i.e., ASPs in the ASP-
ACTIVE state) using DUNA messages for the concerned destinations.
When the SG has completed the MTP Restart procedure, the SUA layer at
the SGPs inform all concerned ASPs in the ASP-ACTIVE state of any
available/restricted SS7 destinations using the DAVA/DRST message.
No message is necessary for those destinations still unavailable
after the restart procedure.
When the SUA layer at an ASP receives a DUNA message indicating SS7
destination unavailability at an SG, SCCP Users will receive an N-
PCSTATE indication and will stop any affected traffic to this
destination. When the SUA receives a DAVA/DRST message, SCCP Users
will receive an N-PCSTATE indication and can resume traffic to the
newly available SS7 destination via this SGP, provided the ASP is in
the ASP-ACTIVE state toward this SGP.
The ASP MAY choose to audit the availability of unavailable
destinations by sending DAUD messages. This would be for example the
case when an AS becomes active at an ASP and does not have current
destination statuses. If MTP restart is in progress at the SG, the
SGP returns a DUNA message for that destination, even if it received
an indication that the destination became available or restricted.
4.7. SCCP - SUA Interworking at the SG
4.7.1. Segmenting / Reassembly
When it is expected that signalling messages will not fit into a PDU
of the most restrictive transport technology used (e.g., 272-SIF of
MTP3), then segmenting/reassembly could be performed at the SG, ASP
or IPSP. If the SG, ASP or IPSP is incapable of performing a
necessary segmentation/reassembly, it can inform the peer of the
failure using the appropriate error in a CLDR or RESRE/COERR message.
4.7.2. Support for Loadsharing
Within an AS (identified by RK/RC parameters) several loadsharing
ASPs may be active.
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However, to assure the correct processing of TCAP transactions or
SCCP connections, the loadsharing scheme used at the SG must make
sure that messages continuing or ending the transactions/connections
arrive at the same ASP where the initial message (TC_Query, TC_Begin,
CR) was sent to/received from.
When the ASP can be identified uniquely based on RK parameters (e.g.,
unique DPC or GT), loadsharing is not required. When the ASPs in the
AS share state or use an internal distribution mechanism, the SG must
only take into account the in-sequence-delivery requirement. In case
of SCCP CO traffic, when the coupled approach is used, loadsharing of
messages other than CR is not required.
If these assumptions cannot be made, both SG and ASP should support
the following general procedure in a loadsharing environment.
4.7.2.1. Association Setup, ASP going active
After association setup and registration, an ASP normally goes active
for each AS it registered for. In the ASPAC message, the ASP
includes a TID and/or DRN Label Parameter, if applicable for the AS
in question. All the ASPs within the AS must specify a unique label
at a fixed position in the TID or DRN parameter. The same ASPAC
message is sent to each SG used for interworking with the SS7
network.
The SG builds, per RK, a list of ASPs that have registered for it.
The SG can now build up and update a distribution table for a certain
Routing Context, any time the association is (re-)established and the
ASP goes active. The SG has to perform some trivial plausibility
checks on the parameters:
- Start and End parameters values are between 0 and 31 for TID.
- Start and End parameters values are between 0 and 23 for DRN
- 0 < (Start - End + 1) <= 16 (label length maximum 16-bit)
- Start values are the same for each ASP within a RC
- End values are the same for each ASP within a RC
- TID and DRN Label values must be unique across the RC
If any of these checks fail, the SG refuses the ASPAC request, with
an error, "Invalid loadsharing label."
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4.7.3. Routing and message distribution at the SG
4.7.3.1. TCAP traffic
Messages not containing a destination (or "responding") TID, i.e.,
Query, Begin, Unidirectional, are loadshared among the available
ASPs. Any scheme permitting a fair load distribution among the ASPs
is allowed (e.g., round robin).
When a destination TID is present, the SG extracts the label and
selects the ASP that corresponds with it.
If an ASP is not available, the SG may generate (X)UDTS "routing
failure", if the return option is used.
4.7.3.2. SCCP Connection Oriented traffic
Messages not containing a destination reference number (DRN), i.e., a
Connection Request, MAY be loadshared among the available ASPs. The
load distribution mechanism is an implementation issue. When a DRN
is present, the SG extracts the label and selects the ASP that
corresponds with it. If an ASP is not available, the SG discards the
message.
4.7.4. Multiple SGs, SUA Relay Function
It is important that each ASP send its unique label (within the AS)
to each SGP. For a better robustness against association failures,
the SGs MAY cooperate to provide alternative routes toward an ASP.
Mechanisms for SG cooperation/coordination are outside of the scope
of this document.
5. Examples of SUA Procedures
The following sequence charts overview the procedures of SUA. These
are meant as examples, they do not, in and of themselves, impose
additional requirements upon an instance of SUA.
5.1. SG Architecture
The sequences below outline logical steps for a variety of scenarios
within a SG architecture. Please note that these scenarios cover a
Primary/Backup configuration. Where there is a load-sharing
configuration then the SGP can declare availability when 1 ASP issues
ASPAC but can only declare unavailability when all ASPs have issued
ASPIA.
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5.1.1. Establishment of SUA connectivity
The following is established before traffic can flow.
Each node is configured (via MIB, for example) with the connections
that need to be setup.
ASP-a1 ASP-a2 SG SEP
(Primary) (Backup)
|------Establish SCTP Association------|
|--Estab. SCTP Ass--|
|--Align SS7 link---|
+----------------ASP Up---------------->
<--------------ASP Up Ack--------------+
+------ASP Up------->
<---ASP Up Ack------+
+-------------ASP Active--------------->
<----------ASP Active Ack--------------+
<----------NTFY (ASP Active)-----------+
<-NTFY (ASP Active)-+
+--------SSA-------->
<--------SSA--------+
<-----------------DAVA-----------------+
+-----------------CLDT----------------->
+--------UDT-------->
5.1.2. Fail-over scenarios
The following sequences address fail-over of SEP and ASP.
5.1.2.1. SEP Fail-over
The SEP knows that the SGP is 'concerned' about its availability.
Similarly, the SGP knows that ASP-a1 is concerned about the SEPs
availability.
ASP-a1 ASP-a2 SG SEP
(Primary) (Backup)
<--------SSP--------+
<-----------------DUNA-----------------+
+-----------------DAUD----------------->
+--------SST-------->
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5.1.2.2. Successful ASP Fail-over scenario
The following is an example of a successful fail-over scenario, where
there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
During the fail-over, the SGP buffers any incoming data messages from
the SEP, forwarding them when the Backup becomes available.
ASP-a1 ASP-a2 SG SEP
(Primary) (Backup)
+-------------ASP Inactive------------->
<-----------ASP Inactive ACK-----------+
<--------------------NTFY (AS Pending)-+
<-NTFY (AS Pending)-+
+----ASP Active----->
<--ASP Active Ack---+
<-NTFY (AS Active)--+
<----------NTFY (AS Active)------------+
5.1.2.3. Unsuccessful ASP Fail-over scenario
ASP-a1 ASP-a2 SG SEP
(Primary) (Backup)
+-------------ASP Inactive------------->
<-----------ASP Inactive ACK-----------+
<--------------------NTFY (AS Pending)-+
<--NTFY (AS Pending)-+
After some time elapses (i.e., timeout).
+--------SSP-------->
<--------SST--------+
<-------------------NTFY (AS Inactive)-+
<-NTFY (AS Inactive)-+
5.2. IPSP Examples
The sequences below outline logical steps for a variety of scenarios
within an IP-IP architecture. Please note that these scenarios cover
a Primary/Backup configuration. Where there is a load-sharing
configuration then the AS can declare availability when 1 ASP issues
ASPAC but can only declare unavailability when all ASPs have issued
ASPIA.
5.2.1. Establishment of SUA connectivity
The following shows an example establishment of SUA connectivity. In
this example, each IPSP consists of an Application Server and two
ASPs. The following is established before SUA traffic can flow. A
connectionless flow is shown for simplicity.
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Establish SCTP Connectivity - as per RFC 2960. Note that SCTP
connections are bidirectional. The endpoint that establishes SCTP
connectivity MUST also establish UA connectivity (see RFC 2960,
section 5.2.1 for handling collisions) [2960].
IP SEP A IP SEP B
AS A AS B
ASP-a1 ASP-a2 ASP-b2 ASP-b1
[All ASPs are in the ASP-DOWN state]
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resources: A resource is an I2RS-specific use of memory, storage,
or execution that a client may consume due to its I2RS operations.
The amount of each such resource that a client may consume in the
context of a particular agent may be constrained based upon the
client's security role. An example of such a resource could
include the number of notifications registered for. These are not
protocol-specific resources or network-specific resources.
role or security role: A security role specifies the scope,
resources, priorities, etc. that a client or agent has.
identity: A client is associated with exactly one specific
identity. State can be attributed to a particular identity. It
is possible for multiple communication channels to use the same
identity; in that case, the assumption is that the associated
client is coordinating such communication.
secondary identity: An I2RS Client may supply a secondary opaque
identity that is not interpreted by the I2RS Agent. An example
use is when the I2RS Client is a go-between for multiple
applications and it is necessary to track which application has
requested a particular operation.
3. Key Architectural Properties
Several key architectural properties for the I2RS protocol are
elucidated below (simplicity, extensibility, and model-driven
programmatic interfaces). However, some architecture principles such
as performance and scaling are not described below because they are
discussed in [I-D.ietf-i2rs-problem-statement] and because the
performance and scaling requires varies based on the particular use-
cases.
3.1. Simplicity
There have been many efforts over the years to improve the access to
the information available to the routing and forwarding system.
Making such information visible and usable to network management and
applications has many well-understood benefits. There are two
related challenges in doing so. First, the quantity and diversity of
information potentially available is very large. Second, the
variation both in the structure of the data and in the kinds of
operations required tends to introduce protocol complexity.
While the types of operations contemplated here are complex in their
nature, it is critical that I2RS be easily deployable and robust.
Adding complexity beyond what is needed to satisfy well known and
understood requirements would hinder the ease of implementation, the
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robustness of the protocol, and the deployability of the protocol.
Overly complex data models tend to ossify information sets by
attempting to describe and close off every possible option,
complicating extensibility.
Thus, one of the key aims for I2RS is the keep the protocol and
modeling architecture simple. So for each architectural component or
aspect, we ask ourselves "do we need this complexity, or is the
behavior merely nice to have?" Protocol parsimony is clearly a goal.
3.2. Extensibility
Naturally, extensibility of the protocol and data model is very
important. In particular, given the necessary scope limitations of
the initial work, it is critical that the initial design include
strong support for extensibility.
The scope of the I2RS work is being restricted in the interests of
achieving a deliverable and deployable result. The I2RS Working
Group is modeling only a subset of the data of interest. It is
clearly desirable for the data models defined in the I2RS to be
useful in more general settings. It should be easy to integrate data
models from the I2RS with other data. Other work should be able to
easily extend it to represent additional aspects of the network
elements or network systems. This reinforces the criticality of
designing the data models to be highly extensible, preferably in a
regular and simple fashion.
The I2RS Working Group is defining operations for the I2RS protocol.
It would be optimistic to assume that more and different ones may not
be needed when the scope of I2RS increases. Thus, it is important to
consider extensibility not only of the underlying services' data
models, but also of the primitives and protocol operations.
3.3. Model-Driven Programmatic Interfaces
A critical component of I2RS is the standard information and data
models with their associated semantics. While many components of the
routing system are standardized, associated data models for them are
not yet available. Instead, each router uses different information,
different mechanisms, and different CLI which makes a standard
interface for use by applications extremely cumbersome to develop and
maintain. Well-known data modeling languages exist and may be used
for defining the data models for I2RS.
There are several key benefits for I2RS in using model-driven
architecture and protocol(s). First, it allows for transferring
data-models whose content is not explicitly implemented or
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understood. Second, tools can automate checking and manipulating
data; this is particularly valuable for both extensibility and for
the ability to easily manipulate and check proprietary data-models.
The different services provided by I2RS can correspond to separate
data-models. An I2RS agent may indicate which data-models are
supported.
4. Security Considerations
This I2RS architecture describes interfaces that clearly require
serious consideration of security. First, here is a brief
description of the assumed security environment for I2RS. The I2RS
Agent associated with a Routing Element is a trusted part of that
Routing Element. For example, it may be part of a vendor-distributed
signed software image for the entire Routing Element or it may be
trusted signed application that an operator has installed. The I2RS
Agent is assumed to have a separate authentication and authorization
channel by which it can validate both the identity and permissions
associated with an I2RS Client. To support numerous and speedy
interactions between the I2RS Agent and I2RS Client, it is assumed
that the I2RS Agent can also cache that particular I2RS Clients are
trusted and their associated authorized scope. This implies that the
permission information may be old either in a pull model until the
I2RS Agent re-requests it, or in a push model until the
authentication and authorization channel can notify the I2RS Agent of
changes.
An I2RS Client is not automatically trustworthy. It has identity
information and applications using that I2RS Client should be aware
of the scope limitations of that I2RS Client. If the I2RS Client is
acting as a broker for multiple applications, managing the security,
authentication and authorization for that communication is out of
scope; nothing prevents I2RS and a separate authentication and
authorization channel from being used. Regardless of mechanism, an
I2RS Client that is acting as a broker is responsible for determining
that applications using it are trusted and permitted to make the
particular requests.
Different levels of integrity, confidentiality, and replay protection
are relevant for different aspects of I2RS. The primary
communication channel that is used for client authentication and then
used by the client to write data requires integrity, privacy and
replay protection. Appropriate selection of a default required
transport protocol is the preferred way of meeting these
requirements.
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Other communications via I2RS may not require integrity,
confidentiality, and replay protection. For instance, if an I2RS
Client subscribes to an information stream of prefix announcements
from OSPF, those may require integrity but probably not
confidentiality or replay protection. Similarly, an information
stream of interface statistics may not even require guaranteed
delivery. In Section 7.2, more reasoning for multiple communication
channels is provided. From the security perspective, it is critical
to realize that an I2RS Agent may open a new communication channel
based upon information provided by an I2RS Client (as described in
Section 7.2). For example, a I2RS client may request notifications
of certain events and the agent will open a communication channel to
report such events. Therefore, to avoid an indirect attack, such a
request must be done in the context of an authenticated and
authorized client whose communications cannot have been altered.
4.1. Identity and Authentication
As discussed above, all control exchanges between the I2RS client and
agent should be authenticated and integrity protected (such that the
contents cannot be changed without detection). Further, manipulation
of the system must be accurately attributable. In an ideal
architecture, even information collection and notification should be
protected; this may be subject to engineering tradeoffs during the
design.
I2RS clients may be operating on behalf of other applications. While
those applications' identities are not needed for authentication or
authorization, each application should have a unique opaque
identifier that can be provided by the I2RS client to the I2RS agent
for purposes of tracking attribution of operations to support
functionality such as accounting and troubleshooting.
4.2. Authorization
All operations using I2RS, both observation and manipulation, should
be subject to appropriate authorization controls. Such authorization
is based on the identity and assigned role of the I2RS client
performing the operations and the I2RS agent in the network element.
I2RS Agents, in performing information collection and manipulation,
will be acting on behalf of the I2RS clients. As such, each
operation authorization will be based on the lower of the two
permissions of the agent itself and of the authenticated client. The
mechanism by which this authorization is applied within the device is
outside of the scope of I2RS.
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The appropriate or necessary level of granularity for scope can
depend upon the particular I2RS Service and the implementation's
granularity. An approach to a similar access control problem is
defined in the NetConf Access Control Model[RFC6536]; it allows
arbitrary access to be specified for a data node instance identifier
while defining meaningful manipulable defaults. The ability to
specify one or more groups or roles that a particular I2RS Client
belongs and then define access controls in terms of those groups or
roles is expected. When a client is authenticated, its group or role
membership should be provided to the I2RS Agent. The set of access
control rules that an I2RS Agent uses would need to be either
provided via Local Config, exposed as an I2RS Service for
manipulation by authorized clients, or via some other method.
5. Network Applications and I2RS Client
I2RS is expected to be used by network-oriented applications in
different architectures. While the interface between a network-
oriented application and the I2RS client is outside the scope of
I2RS, considering the different architectures is important to
sufficiently specify I2RS.
In the simplest architecture, a network-oriented application has an
I2RS client as a library or driver for communication with routing
elements.
In the broker architecture, multiple network-oriented applications
communicate in an unspecified fashion to a broker application that
contains an I2RS Client. That broker application requires additional
functionality for authentication and authorization of the network-
oriented applications; such functionality is out of scope for I2RS
but similar considerations to those described in Section 4.2 do
apply. As discussed in Section 4.1, the broker I2RS Client should
determine distinct opaque identifiers for each network-oriented
application that is using it. The broker I2RS Client can pass along
the appropriate value as a secondary identifier which can be used for
tracking attribution of operations.
In a third architecture, a routing element or network-oriented
application that uses an I2RS Client to access services on a
different routing element may also contain an I2RS agent to provide
services to other network-oriented applications. However, where the
needed information and data models for those services differs from
that of a conventional routing element, those models are, at least
initially, out of scope for I2RS. Below is an example of such a
network application
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5.1. Example Network Application: Topology Manager
A Topology Manager includes an I2RS client that uses the I2RS data
models and protocol to collect information about the state of the
network by communicating directly with one or more I2RS agents. From
these I2RS agents, the Topology Manager collects routing
configuration and operational data, such as interface and label-
switched path (LSP) information. In addition, the Topology Manager
may collect link-state data in several ways - either via I2RS models,
by peering with BGP-LS[I-D.ietf-idr-ls-distribution] or listening
into the IGP.
The set of functionality and collected information that is the
Topology Manager may be embedded as a component of a larger
application, such as a path computation application. As a stand-
alone application, the Topology Manager could be useful to other
network applications by providing a coherent picture of the network
state accessible via another interface. That interface might use the
same I2RS protocol and could provide a topology service using
extensions to the I2RS data models.
6. I2RS Agent Role and Functionality
The I2RS Agent is part of a routing element. As such, it has
relationships with that routing element as a whole, and with various
components of that routing element.
6.1. Relationship to its Routing Element
A Routing Element may be implemented with a wide variety of different
architectures: an integrated router, a split architecture,
distributed architecture, etc. The architecture does not need to
affect the general I2RS agent behavior.
For scalability and generality, the I2RS agent may be responsible for
collecting and delivering large amounts of data from various parts of
the routing element. Those parts may or may not actually be part of
a single physical device. Thus, for scalability and robustness, it
is important that the architecture allow for a distributed set of
reporting components providing collected data from the I2RS agent
back to the relevant I2RS clients. There may be multiple I2RS Agents
within the same router. In such a case, they must have non-
overlapping sets of information which they manipulate.
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6.2. I2RS State Storage
State modification requests are sent to the I2RS agent in a routing
element by I2RS clients. The I2RS agent is responsible for applying
these changes to the system, subject to the authorization discussed
above. The I2RS agent will retain knowledge of the changes it has
applied, and the client on whose behalf it applied the changes. The
I2RS agent will also store active subscriptions. These sets of data
form the I2RS data store. This data is retained by the agent until
the state is removed by the client, overridden by some other
operation such as CLI, or the device reboots. Meaningful logging of
the application and removal of changes is recommended. I2RS applied
changes to the routing element state will not be retained across
routing element reboot. The I2RS data store is not preserved across
routing element reboots; thus the I2RS agent will not attempt to
reapply such changes after a reboot.
6.2.1. I2RS Agent Failure
It is expected that an I2RS Agent may fail independently of the
associated routing element. This could happen because I2RS is
disabled on the routing element or because the I2RS Agent, a separate
process or even running on a separate processor, experiences an
unexpected failure. Just as routing state learned from a failed
source is removed, the ephemeral I2RS state will usually be removed
shortly after the failure is detected or as part of a graceful
shutdown process. To handle I2RS Agent failure, the I2RS Agent must
use two different notifications.
NOTIFICATION_I2RS_AGENT_STARTING: This notification identifies that
the associated I2RS Agent has started. It includes an agent-boot-
count that indicates how many times the I2RS Agent has restarted
since the associated routing element restarted. The agent-boot-
count allows an I2RS Client to determine if the I2RS Agent has
restarted.
NOTIFICATION_I2RS_AGENT_TERMINATING: This notification reports that
the associated I2RS Agent is shutting down gracefully. Ephemeral
state will be removed. It can optionally include a timestamp
indicating when the I2RS Agent will shutdown. Use of this
timestamp assumes that time synchronization has been done and the
timestamp should not have granularity finer than one second
because better accuracy of shutdown time is not guaranteed.
There are two different failure types that are possible and each has
different behavior.
>
<-----------------------------ASP Up Ack------------------------+
+--------------ASP Up--------------->
<------------ASP Up Ack-------------+
+---------------------------ACTIVE------------------------------->
<-------------------------ACTIVE Ack-----------------------------+
[Traffic can now flow directly between ASPs]
+-----------------------------CLDT------------------------------->
5.2.2. Fail-over scenarios
The following sequences address fail-over of ASP.
5.2.2.1. Successful ASP Fail-over scenario
The following is an example of a successful fail-over scenario, where
there is a fail-over from ASP-a1 to ASP-a2, i.e., Primary to Backup.
Since data transfer passes directly between peer ASPs, ASP-b1 is
notified of the fail-over of ASP-a1 and buffers outgoing data
messages until ASP-a2 becomes available.
IP SEP A IP SEP B
ASP-a1 ASP-a2 ASP-b2 ASP-b1
+-----------------------------ASP Inact------------------------>
<---------------------------ASP Inact Ack----------------------+
<---------------NTFY (ASP-a1 Inactive)--------------+
+---------------------ASP Act----------------------->
<-------------------ASP Act Ack---------------------+
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5.2.2.2. Unsuccessful ASP Fail-over scenario
The sequence is the same as 5.2.2.1 except that, since the backup
fails to come in then, the Notify messages declaring the availability
of the backup are not sent.
6. Security Considerations
The security considerations discussed for the 'Security
Considerations for SIGTRAN Protocols' [3788] document apply to this
document.
7. IANA Considerations
7.1. SCTP Payload Protocol ID
IANA has assigned a SUA value for the Payload Protocol Identifier in
the SCTP DATA chunk. The following SCTP Payload Protocol Identifier
is registered:
SUA "4"
The SCTP Payload Protocol Identifier value "4" SHOULD be included in
each SCTP DATA chunk, to indicate that the SCTP is carrying the SUA
protocol. The value "0" (unspecified) is also allowed but any other
values MUST not be used. This Payload Protocol Identifier is not
directly used by SCTP but MAY be used by certain network entities to
identify the type of information being carried in a DATA chunk.
The User Adaptation peer MAY use the Payload Protocol Identifier, as
a way of determining additional information about the data being
presented to it by SCTP.
7.2. Port Number
IANA has registered SCTP Port Number 14001 for SUA. It is
recommended that SGPs use this SCTP port number for listening for new
connections. SGPs MAY also use statically configured SCTP port
numbers instead.
7.3. Protocol Extensions
This protocol may also be extended through IANA in three ways:
- Through definition of additional message classes.
- Through definition of additional message types.
- Through definition of additional message parameters.
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The definition and use of new message classes, types and parameters
is an integral part of SIGTRAN adaptation layers. Thus, these
extensions are assigned by IANA through an IETF Consensus action as
defined in [2434].
The proposed extension MUST in no way adversely affect the general
working of the protocol.
A new registry has been created by IANA to allow the protocol to be
extended.
7.3.1. IETF Defined Message Classes
The documentation for a new message class MUST include the following
information:
(a) A long and short name for the message class;
(b) A detailed description of the purpose of the message class.
7.3.2. IETF Defined Message Types
Documentation of the message type MUST contain the following
information:
(a) A long and short name for the new message type;
(b) A detailed description of the structure of the message.
(c) A detailed definition and description of intended use of each
field within the message.
(d) A detailed procedural description of the use of the new message
type within the operation of the protocol.
(e) A detailed description of error conditions when receiving this
message type.
When an implementation receives a message type which it does not
support, it MUST respond with an Error (ERR) message, with an Error
Code = Unsupported Message Type.
7.3.4. IETF-defined TLV Parameter Extension
Documentation of the message parameter MUST contain the following
information:
(a) Name of the parameter type.
(b) Detailed description of the structure of the parameter field.
This structure MUST conform to the general type-length-value
format described earlier in the document.
(c) Detailed definition of each component of the parameter value.
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(d) Detailed description of the intended use of this parameter type,
and an indication of whether and under what circumstances
multiple instances of this parameter type may be found within the
same message type.
8. Timer Values
Ta 2 seconds
Tr 2 seconds
T(ack) 2 seconds
T(ias) Inactivity Send timer 7 minutes
T(iar) Inactivity Receive timer 15 minutes
T(beat) Heartbeat Timer 30 seconds
9. Acknowledgements
The authors would like to thank (in alphabetical order) Richard
Adams, Javier Pastor-Balbas, Andrew Booth, Martin Booyens, F.
Escobar, S. Furniss Klaus Gradischnig, Miguel A. Garcia, Marja-Liisa
Hamalainen, Sherry Karl, S. Lorusso, Markus Maanoja, Sandeep Mahajan,
Ken Morneault, Guy Mousseau, Chirayu Patel, Michael Purcell, W.
Sully, Michael Tuexen, Al Varney, Tim Vetter, Antonio Villena, Ben
Wilson, Michael Wright and James Yu for their insightful comments and
suggestions.
10. References
10.1. Normative References
[1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123, October
1989.
[2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 2000.
[3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[3788] Loughney, J., Tuexen, M., Ed., and J. Pastor-Balbas,
"Security Considerations for Signaling Transport
(SIGTRAN) Protocols", RFC 3788, June 2004.
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[ANSI SCCP] ANSI T1.112 "Signalling System Number 7 - Signalling
Connection Control Part".
[ITU SCCP] ITU-T Recommendations Q.711-714, "Signalling System
No. 7 (SS7) - Signalling Connection Control Part
(SCCP)." ITU-T Telecommunication Standardization
Sector of ITU, formerly CCITT, Geneva (July 1996).
10.2. Informative References
[2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H.,
Coene, L., Lin, H., Juhasz, I., Holdrege, M., and C.
Sharp, "Framework Architecture for Signalling
Transport", RFC 2719, October 1999.
[3761] Falstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation
Discovery System (DDDS) Application (ENUM)", RFC 3761,
April 2004.
[ANSI TCAP] ANSI T1.114 'Signalling System Number 7 - Transaction
Capabilities Application Part'
[ITU TCAP] ITU-T Recommendation Q.771-775 'Signalling System No.
7 SS7) - Transaction Capabilities (TCAP).'
[RANAP] 3G TS 25.413 V3.5.0 (2001-03) 'Technical Specification
3rd Generation Partnership Project; Technical
Specification Group Radio Access Network; UTRAN Iu
Interface RANAP Signalling'
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Appendix A. Signalling Network Architecture
A.1. Generalized Peer-to-Peer Network Architecture
Figure 3 shows an example network architecture that can support
robust operation and fail-over. There needs to be some management
resources at the AS to manage traffic.
***********
* AS1 *
* +-----+ * SCTP Associations
* |ASP1 +-------------------+
* +-----+ * | ***********
* * | * AS3 *
* +-----+ * | * +-----+ *
* |ASP2 +-----------------------------------------+ASP1 | *
* +-----+ * | * +-----+ *
* * | * *
* +-----+ * | * +-----+ *
* |ASP3 | * +--------------------------+ASP2 | *
* +-----+ * | | * +-----+ *
*********** | | ***********
| |
*********** | | ***********
* AS2 * | | * AS4 *
* +-----+ * | | * +-----+ *
* |ASP1 +--------------+ +---------------------+ASP1 | *
* +-----+ * * +-----+ *
* * * *
* +-----+ * * +-----+ *
* |ASP2 +-----------------------------------------+ASP1 | *
* +-----+ * * +-----+ *
* * ***********
* +-----+ *
* |ASP3 | *
* +-----+ *
* *
***********
Figure 3: Generalized Architecture
In this example, the Application Servers are shown residing within
one logical box, with ASPs located inside. In fact, an AS could be
distributed among several hosts. In such a scenario, the host should
share state as protection in the case of a failure. This is out of
scope of this protocol. Additionally, in a distributed system, one
ASP could be registered to more than one AS. This document should
not restrict such systems - though such a case in not specified.
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A.2. Signalling Gateway Network Architecture
When interworking between SS7 and IP domains is needed, the SGP acts
as the gateway node between the SS7 network and the IP network. The
SGP will transport SCCP-user signalling traffic from the SS7 network
to the IP-based signalling nodes (for example IP-resident Databases).
The Signalling Gateway can be considered as a group of Application
Servers with additional functionality to interface toward an SS7
network.
The SUA protocol should be flexible enough to allow different
configurations and transport technology to allow the network
operators to meet their operation, management and performance
requirements.
An ASP may be connected to multiple SGPs (see figure 4). In such a
case, a particular SS7 destination may be reachable via more than SG,
therefore, more than one route. Given that proper SLS selection,
loadsharing, and SG selection based on point code availability is
performed at the ASP, it will be necessary for the ASP to maintain
the status of each distant SGPs to which it communicates on the basis
of the SG through which it may route.
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Signalling Gateway
SCTP Associations
+----------+ **************
| SG1 | * AS3 *
| ******** | * ******** *
| * SGP11+--------------------------------------------+ ASP1 * *
| ******** | / * ******** *
| ******** | | * ******** *
| * SGP12+--------------------------------------------+ ASP2 * *
| ******** | \ / | * ******** *
+----------+ \ | | * . *
\ | | * . *
+---------- \ | | * . *
| SG2 | \ | | * . *
| ******** | \ | | * ******** *
| * SGP21+---------------------------------+-+ * * ASPN * *
| ******** | \ * ******** *
| ******** | \ **************
| * SGP22+---+--+ \
| ******** | | | \ **************
+----------+ | | \ * AS4 *
| | \ * ******** *
| +-------------------------------------+ ASP1 * *
| * ******** *
| * . *
| * . *
| * *
| * ******** *
+----------------------------------------+ ASPn * *
* ******** *
**************
Figure 4: Signalling Gateway Architecture
The pair of SGs can either operate as replicated endpoints or as
replicated relay points from the SS7 network point of view.
Replicated endpoints: the coupling between the SGs and the ASPs when
the SGs act as replicated endpoints is an implementation issue.
Replicated relay points: in normal circumstances, the path from SEP
to ASP will always go via the same SGP when in-sequence-delivery is
requested. However, linkset failures may cause MTP to reroute to the
other SG.
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A.3. Signalling Gateway Message Distribution Recommendations
A.3.1. Connectionless Transport
By means of configuration, the SG knows the local SCCP-user is
actually represented by an AS, and serviced by a set of ASPs working
in n+k redundancy mode. An ASP is selected and a CLDT message is
sent on the appropriate SCTP association/stream.
The selection criterion can be based on a round robin mechanism, or
any other method that guarantees a balanced loadsharing over the
active ASPs. However, when TCAP messages are transported, load
sharing is only possible for the first message in a TCAP dialogue
(TC_Begin, TC_Query, TC_Unidirectional). All other TCAP messages in
the same dialogue are sent to the same ASP that was selected for the
first message, unless the ASPs are able to share state and maintain
sequenced delivery. To this end, the SGP needs to know the TID
allocation policy of the ASPs in a single AS:
- State sharing
- Fixed range of TIDs per ASP in the AS
This information may be provisioned in the SG, or may be dynamically
exchanged via the ASP_Active message.
An example for an INAP/TCAP message exchange between SEP and ASP is
given below.
Address information in CLDT message (e.g., TC_Query) from SGP to ASP,
with association ID = SG-ASP, Stream ID based on sequence control and
possibly other parameters, e.g., OPC:
- Routing Context: based on SS7 Network ID and AS membership, so
that the message can be transported to the correct ASP.
- Source address: valid combination of SSN, PC and GT, as needed for
back routing to the SEP.
- Destination address: at least SSN, to select the SCCP/SUA-user at
the ASP.
Address information in CLDT message (e.g., TC_Response) from ASP to
SG, with association ID = ASP-SG, stream ID selected by
implementation dependent means with regards to in-sequence-delivery:
- Routing Context: as received in previous message.
- Source address: unique address provided so that when used as the
SCCP called party address in the SEP, it must yield the same AS,
the SSN might be sufficient.
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Unexpected failure: In this case, the I2RS Agent has unexpectedly
crashed and thus cannot notify its clients of anything. Since
I2RS does not require a persistent connection between the I2RS
Client and I2RS Agent, it is necessary to have a mechanism for the
I2RS Agent to notify I2RS Clients that had subscriptions or
written ephemeral state; such I2RS Clients should be cached by the
I2RS Agent's system in persistent storage. When the I2RS Agent
starts, it should send a NOTIFICATION_I2RS_AGENT_STARTING to each
cached I2RS Client.
Graceful failure: In this case, the I2RS Agent can do specific
limited work as part of the process of being disabled. The I2RS
Agent Agent must send a NOTIFICATION_I2RS_AGENT_TERMINATING to all
its cached I2RS Clients.
6.2.2. Starting and Ending
When an I2RS client applies changes via the I2RS protocol, those
changes are applied and left until removed or the routing element
reboots. The network application may make decisions about what to
request via I2RS based upon a variety of conditions that imply
different start times and stop times. That complexity is managed by
the network application and is not handled by I2RS.
6.2.3. Reversion
An I2RS Agent may decide that some state should no longer be applied.
An I2RS Client may instruct an Agent to remove state it has applied.
In all such cases, the state will revert to what it would have been
without the I2RS; that state is generally whatever was specified via
the CLI, NETCONF, SNMP, etc. I2RS Agents will not store multiple
alternative states, nor try to determine which one among such a
plurality it should fall back to. Thus, the model followed is not
like the RIB, where multiple routes are stored at different
preferences.
An I2RS Client may register for notifications, subject to its
notification scope, regarding state modification or removal by a
particular I2RS Client.
6.3. Interactions with Local Config
Changes may originate from either Local Config or from I2RS. The
modifications and data stored by I2RS are separate from the local
device configuration, but conflicts between the two must be resolved
in a deterministic manner that respects operator-applied policy.
That policy can determine whether Local Config overrides a particular
I2RS client's request or vice versa. To achieve this end, either by
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default Local Config always wins or, optionally, a routing element
may permit a priority to be configured on the device for the Local
Config mechanism. The policy mechanism in the later case is
comparing the I2RS client's priority with that priority assigned to
the Local Config.
When the Local Config always wins, some communication between that
subsystem and the I2RS Agent is still necessary. That communication
contains the details of each specific device configuration change
that the I2RS Agent is permitted to modify. In addition, when the
system determines, that a client's I2RS state is preempted, the I2RS
agent must notify the affected I2RS clients; how the system
determines this is implementation-dependent.
It is critical that policy based upon the source is used because the
resolution cannot be time-based. Simply allowing the most recent
state to prevail could cause race conditions where the final state is
not repeatably deterministic.
6.4. Routing Components and Associated I2RS Services
For simplicity, each logical protocol or set of functionality that
can be compactly described in a separable information and data model
is considered as a separate I2RS Service. A routing element need not
implement all routing components described nor provide the associated
I2RS services. When a full implementation is not mandatory, an I2RS
Service should include a capability model so that implementations can
indicate which parts of the service are supported. Each I2RS Service
requires an information model that describes at least the following:
data that can be read, data that can be written, notifications that
can be subscribed to, and the capability model mentioned above.
The initial services included in the I2RS architecture are as
follows.
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*************************** ************** *****************
* I2RS Protocol * * * * Dynamic *
* * * Interfaces * * Data & *
* +--------+ +-------+ * * * * Statistics *
* | Client | | Agent | * ************** *****************
* +--------+ +-------+ *
* * ************** *************
*************************** * * * *
* Policy * * Base QoS *
******************** ******** * Templates * * Templates *
* +--------+ * * * * * *************
* BGP | BGP-LS | * * PIM * **************
* +--------+ * * *
******************** ******** ****************************
* MPLS +---------+ +-----+ *
********************************** * | RSVP-TE | | LDP | *
* IGPs +------+ +------+ * * +---------+ +-----+ *
* +--------+ | OSPF | | ISIS | * * +--------+ *
* | Common | +------+ +------+ * * | Common | *
* +--------+ * * +--------+ *
********************************** ****************************
**************************************************************
* RIB Manager *
* +-------------------+ +---------------+ +------------+ *
* | Unicast/multicast | | Policy-Based | | RIB Policy | *
* | RIBs & LIBs | | Routing | | Controls | *
* | route instances | | (ACLs, etc) | +------------+ *
* +-------------------+ +---------------+ *
**************************************************************
Figure 2: Anticipated I2RS Services
There are relationships between different I2RS Services - whether
those be the need for the RIB to refer to specific interfaces, the
desire to refer to common complex types (e.g. links, nodes, IP
addresses), or the ability to refer to implementation-specific
functionality (e.g. pre-defined templates to be applied to interfaces
or for QoS behaviors that traffic is direct into). Section 6.4.5
discusses information modeling constructs and the range of
relationship types that are applicable.
6.4.1. Routing and Label Information Bases
Routing elements may maintain one or more Information Bases.
Examples include Routing Information Bases such as IPv4/IPv6 Unicast
or IPv4/IPv6 Multicast. Another such example includes the MPLS Label
Information Bases, per-platform- or per-interface." This
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functionality, exposed via an I2RS Service, must interact smoothly
with the same mechanisms that the routing element already uses to
handle RIB input from multiple sources, so as to safely change the
system state. Conceptually, this can be handled by having the I2RS
Agent communicate with a RIB Manager as a separate routing source.
The point-to-multipoint state added to the RIB does not need to match
to well-known multicast protocol installed state. The I2RS Agent can
create arbitrary replication state in the RIB, subject to the
advertised capabilities of the routing element.
6.4.2. IGPs, BGP and Multicast Protocols
A separate I2RS Service can expose each routing protocol on the
device. Such I2RS services may include a number of different kinds
of operations:
o reading the various internal RIB(s) of the routing protocol is
often helpful for understanding the state of the network.
Directly writing to these protocol-specific RIBs or databases is
out of scope for I2RS.
o reading the various pieces of policy information the particular
protocol instance is using to drive its operations.
o writing policy information such as interface attributes that are
specific to the routing protocol or BGP policy that may indirectly
manipulate attributes of routes carried in BGP.
o writing routes or prefixes to be advertised via the protocol.
o joining/removing interfaces from the multicast trees
o subscribing to an information stream of route changes
o receiving notifications about peers coming up or going down
For example, the interaction with OSPF might include modifying the
local routing element's link metrics, announcing a locally-attached
prefix, or reading some of the OSPF link-state database. However,
direct modification of the link-state database MUST NOT be allowed in
order to preserve network state consistency.
6.4.3. MPLS
I2RS Services will be needed to expose the protocols that create
transport LSPs (e.g. LDP and RSVP-TE) as well as protocols (e.g.
BGP, LDP) that provide MPLS-based services (e.g. pseudowires, L3VPNs,
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L2VPNs, etc). This should include all local information about LSPs
originating in, transiting, or terminating in this Routing Element.
6.4.4. Policy and QoS Mechanisms
Many network elements have separate policy and QoS mechanisms,
including knobs which affect local path computation and queue control
capabilities. These capabilities vary widely across implementations,
and I2RS cannot model the full range of information collection or
manipulation of these attributes. A core set does need to be
included in the I2RS information models and supported in the expected
interfaces between the I2RS Agent and the network element, in order
to provide basic capabilities and the hooks for future extensibility.
By taking advantage of extensibility and sub-classing, information
models can specify use of a basic model that can be replaced by a
more detailed model.
6.4.5. Information Modeling, Device Variation, and Information
Relationships
I2RS depends heavily on information models of the relevant aspects of
the Routing Elements to be manipulated. These models drive the data
models and protocol operations for I2RS. It is important that these
informational models deal well with a wide variety of actual
implementations of Routing Elements, as seen between different
products and different vendors. There are three ways that I2RS
information models can address these variations: class or type
inheritance, optional features, and templating.
6.4.5.1. Managing Variation: Object Classes/Types and Inheritance
Information modelled by I2RS from a Routing Element can be described
in terms of classes or types or object. Different valid inheritance
definitions can apply. What is appropriate for I2RS to use is not
determined in this architecture; for simplicity, class and subclass
will be used as the example terminology. This I2RS architecture does
require the ability to address variation in Routing Elements by
allowing information models to define parent or base classes and
subclasses.
The base or parent class defines the common aspects that all Routing
Elements are expected to support. Individual subclasses can
represent variations and additional capabilities. When applicable,
there may be several levels of refinement. The I2RS protocol can
then provide mechanisms to allow an I2RS client to determine which
classes a given I2RS Agent has available. Clients which only want
basic capabilities can operate purely in terms of base or parent
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classes, while a client needing more details or features can work
with the supported sub-class(es).
As part of I2RS information modeling, clear rules should be specified
for how the parent class and subclass can relate; for example, what
changes can a subclass make to its parent? The description of such
rules should be done so that it can apply across data modeling tools
until the I2RS data modeling language is selected.
6.4.5.2. Managing Variation: Optionality
I2RS Information Models must be clear about what aspects are
optional. For instance, must an instance of a class always contain a
particular data field X? If so, must the client provide a value for
X when creating the object or is there a well-defined default value?
From the Routing Element perspective, in the above example, each
Information model should provide information that:
o Is X required for the data field to be accepted and applied?
o If X is optional, then how does "X" as an optional portion of data
field interact with the required aspects of the data field?
o Does the data field have defaults for the mandatory portion of the
field and the optional portions of the field
o Is X required to be within a particular set of values (E.g. range,
length of strings)?
The information model needs to be clear about what read or write
values are set by client and what responses or actions are required
by the agent. It is important to indicate what is required or
optional in client values and agent responses/actions.
6.4.5.3. Managing Variation: Templating
A template is a collection of information to address a problem; it
cuts across the notions of class and object instances. A template
provides a set of defined values for a set of information fields and
can specify a set of values that must be provided to complete the
template. Further, a flexible template scheme may that some of the
defined values can be over-written.
For instance, assigning traffic to a particular service class might
be done by specifying a template Queueing with a parameter to
indicate Gold, Silver, or Best Effort. The details of how that is
carried out are not modeled. This does assume that the necessary
templates are made available on the Routing Element via some
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mechanism other than I2RS. The idea is that by providing suitable
templates for tasks that need to be accomplished, with templates
implemented differently for different kinds of Routing Elements, the
client can easily interact with the Routing Element without concern
for the variations which are handled by values included in the
template.
If implementation variation can be exposed in other ways, templates
may not be needed. However, templates themselves could be objects
referenced in the protocol messages, with Routing Elements being
configured with the proper templates to complete the operation. This
is a topic for further discussion.
6.4.5.4. Object Relationships
Objects (in a Routing Element or otherwise) do not exist in
isolation. They are related to each other. One of the important
things a class definition does is represent the relationships between
instances of different classes. These relationships can be very
simple, or quite complicated. The following lists the information
relationships that the information models need to support.
[[Editors' note: All of these are for discussion, and it is expected
that the list may be changed during WG discussion.]]
6.4.5.4.1. Initialization
The simplest relationship is that one object instance is initialized
by copying another. For example, one may have an object instance
that represents the default setup for a tunnel, and all new tunnels
have fields copied from there if they are not set as part of
establishment. This is closely related to the templates discussed
above, but not identical. Since the relationship is only momentary
it is often not formally represented in modeling, but only captured
in the semantic description of the default object.
6.4.5.4.2. Correlation Identification
Often, it suffices to indicate in one object that it is related to a
second object, without having a strong binding between the two. So
an Identifier is used to represent the relationship. This can be
used to allow for late binding, or a weak binding that does not even
need to exist. A policy name in an object might indicate that if a
policy by that name exists, it is to be applied under some
circumstance. In modeling this is often represented by the type of
the value.
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6.4.5.4.3. Object References
Sometimes the relationship between objects is stronger. A valid ARP
entry has to point to the active interface over which it was derived.
This is the classic meaning of an object reference in programming.
It can be used for relationships like containment or dependence.
This is usually represented by an explicit modeling link.
6.4.5.4.4. Active Reference
There is an even stronger form of coupling between objects if changes
in one of the two objects are always to be reflected in the state of
the other. For example, if a Tunnel has an MTU, and link MTU changes
need to immediately propagate to the Tunnel MTU, then the tunnel is
actively coupled to the link interface. This kind of active state
coupling implies some sort of internal bookkeeping to ensure
consistency, often conceptualized as a subscription model across
objects.
7. I2RS Client Agent Interface
7.1. One Control and Data Exchange Protocol
As agreed by the I2RS working group, this I2RS architecture assumes
that there is a single I2RS protocol for control and data exchange;
that protocol will be based on NETCONF[RFC6241] and RESTCONF
[I-D.ietf-netconf-restconf]. This helps meet the goal of simplicity
and thereby enhances deployability. That protocol may need to use
several underlying transports (TCP, SCTP, DCCP), with suitable
authentication and integrity protection mechanisms. These different
transports can support different types of communication (e.g.
control, reading, notifications, and information collection) and
different sets of data. Whatever transport is used for the data
exchange, it must also support suitable congestion control
mechanisms. The transports chosen should be operator and implementor
friendly to ease adoption.
7.2. Communication Channels
Multiple communication channels and multiple types of communication
channels are required. There may be a range of requirements (e.g.
confidentiality, reliability), and to support the scaling there may
need to be channels originating from multiple sub-components of a
routing element and/or to multiple parts of an I2RS client. All such
communication channels will use the same higher level protocol. Use
of additional channels for communication will be coordinated between
the I2RS client and the I2RS agent.
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I2RS protocol communication can be delivered in-band via the routing
system's data plane. I2RS protocol communication might be delivered
out-of-band via a management interface. Depending on what operations
are requested, it is possible for the I2RS protocol communication to
cause the in-band communication channels to stop working; this could
cause the I2RS agent to become unreachable across that communication
channel.
7.3. Capability Negotiation
The support for different protocol capabilities and I2RS Services
will vary across I2RS Clients and Routing Elements supporting I2RS
Agents. Since each I2RS Service is required to include a capability
model (see Section 6.4), negotiation at the protocol level can be
restricted to protocol specifics and which I2RS Services are
supported.
Capability negotiation (such as which transports are supported beyond
the minimum required to implement) will clearly be necessary. It is
important that such negotiations be kept simple and robust, as such
mechanisms are often a source of difficulty in implementation and
deployment.
The protocol capability negotiation can be segmented into the basic
version negotiation (required to ensure basic communication), and the
more complex capability exchange which can take place within the base
protocol mechanisms. In particular, the more complex protocol and
mechanism negotiation can be addressed by defining information models
for both the I2RS Agent and the I2RS Client. These information
models can describe the various capability options. This can then
represent and be used to communicate important information about the
agent, and the capabilities thereof.
7.4. Identity and Security Role
Each I2RS Client will have a unique identity; it can also have
secondary identities to be used for troubleshooting. A secondary
identity is merely a unique, opaque identifier that may be helpful in
troubleshooting. Via authentication and authorization mechanisms
based on the primary unique identity, the I2RS Client will have a
specific scope for reading data, for writing data, and limitations on
the resources that can be consumed. The scopes need to specify both
the data and the value ranges.
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7.4.1. Client Redundancy
I2RS must support client redundancy. At the simplest, this can be
handled by having a primary and a backup network application that
both use the same client identity and can successfully authenticate
as such. Since I2RS does not require a continuous transport
connection and supports multiple transport sessions, this can provide
some basic redundancy. However, it does not address concerns for
troubleshooting and accountability about knowing which network
application is actually active. At a minimum, basic transport
information about each connection and time can be logged with the
identity.
7.5. Connectivity
A client may or may not maintain an active communication channel with
an agent. Therefore, an agent may need to open a communication
channel to the client to communicate previously requested
information. The lack of an active communication channel does not
imply that the associated client is non-functional. When
communication is required, the agent or client can open a new
communication channel.
State held by an agent that is owned by a client should not be
removed or cleaned up when a client is no longer communicating - even
if the agent cannot successfully open a new communication channel to
the client.
For many applications, it may be desirable to clean up state if a
network application dies before removing the state it has created.
Typically, this is dealt with in terms of network application
redundancy. If stronger mechanisms are desired, mechanisms outside
of I2RS may allow a supervisory network application to monitor I2RS
clients, and based on policy known to the supervisor clean up state
if applications die. More complex mechanism instantiated in the I2RS
agent would add complications to the I2RS protocol and are thus left
for future work.
Some examples of such a mechanism include the following. In one
option, the client could request state clean-up if a particular
transport session is terminated. The second is to allow state
expiration, expressed as a policy associated with the I2RS client's
role. The state expiration could occur after there has been no
successful communication channel to or from the I2RS client for the
policy-specified duration.
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7.6. Notifications
As with any policy system interacting with the network, the I2RS
Client needs to be able to receive notifications of changes in
network state. Notifications here refers to changes which are
unanticipated, represent events outside the control of the systems
(such as interface failures on controlled devices), or are
sufficiently sparse as to be anomalous in some fashion. A
notification may also be due to a regular event.
Such events may be of interest to multiple I2RS Clients controlling
data handled by an I2RS Agent, and to multiple other I2RS clients
which are collecting information without exerting control. The
architecture therefore requires that it be practical for I2RS Clients
to register for a range of notifications, and for the I2RS Agents to
send notifications to a number of Clients. The I2RS Client should be
able to filter the specific notifications that will be received; the
specific types of events and filtering operations can vary by
information model and need to be specified as part of the information
model.
The I2RS information model needs to include representation of these
events. As discussed earlier, the capability information in the
model will allow I2RS clients to understand which events a given I2RS
Agent is capable of generating.
For performance and scaling by the I2RS client and general
information privacy, an I2RS Client needs to be able to register for
just the events it is interested in. It is also possible that I2RS
might might provide a stream of notifications via a publish/subscribe
mechanism that is not amenable to having the I2RS agent do the
filtering.
7.7. Information collection
One of the other important aspects of the I2RS is that it is intended
to simplify collecting information about the state of network
elements. This includes both getting a snapshot of a large amount of
data about the current state of the network element, and subscribing
to a feed of the ongoing changes to the set of data or a subset
thereof. This is considered architecturally separate from
notifications due to the differences in information rate and total
volume.
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7.8. Multi-Headed Control
As was described earlier, an I2RS Agent interacts with multiple I2RS
Clients who are actively controlling the network element. From an
architecture and design perspective, the assumption is that by means
outside of this system the data to be manipulated within the network
element is appropriately partitioned so that any given piece of
information is only being manipulated by a single I2RS Client.
Nonetheless, unexpected interactions happen and two (or more) I2RS
clients may attempt to manipulate the same piece of data. This is
considered an error case. This architecture does not attempt to
determine what the right state of data should be when such a
collision happens. Rather, the architecture mandates that there be
decidable means by which I2RS Agents handle the collisions. The
mechanism for ensuring predictability is to have a simple priority
associated with each I2RS clients, and the highest priority change
remains in effect. In the case of priority ties, the first client
whose attribution is associated with the data will keep control.
In order for this approach to multi-headed control to be useful for
I2RS Clients, it is important that it be possible for an I2RS Client
to register for changes to any changes made by I2RS to data that it
may care about. This is included in the I2RS event mechanisms. This
also needs to apply to changes made by CLI/NETCONF/SNMP within the
write-scope of the I2RS Agent, as the same priority mechanism (even
if it is "CLI always wins") applies there. The I2RS client may then
respond to the situation as it sees fit.
7.9. Transactions
In the interest of simplicity, the I2RS architecture does not include
multi-message atomicity and rollback mechanisms. Rather, it includes
a small range of error handling for a set of operations included in a
single message. An I2RS Client may indicate one of the following
three error handling for a given message with multiple operations
which it sends to an I2RS Agent:
Perform all or none: This traditional SNMP semantic indicates that
other I2RS agent will keep enough state when handling a single
message to roll back the operations within that message. Either
all the operations will succeed, or none of them will be applied
and an error message will report the single failure which caused
them not to be applied. This is useful when there are, for
example, mutual dependencies across operations in the message.
Perform until error: In this case, the operations in the message
are applied in the specified order. When an error occurs, no
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- Destination address: copied from source address in received CLDT
message.
Further messages from the SEP belonging to the same TCAP transaction
will now reach the same ASP.
A.3.2. Connection-Oriented Transport
Further messages for this connection are routed on DPC in the SS7
connection section (MTP routing label), and on IP address in the IP
connection section (SCTP header). No other routing information is
present in the SCCP or SUA messages themselves. Resources are kept
within the SG to forward messages from one section to another and to
populate the MTP routing label or SCTP header, based on the
destination local reference of these messages (Connect Confirm, Data
Transfer, etc.)
This means that in the SG, two local references are allocated, one
3-byte value used for the SS7 section and one 4-byte value for the IP
section. Also a resource containing the connection data for both
sections is allocated, and either of the two local references can be
used to retrieve this data e.g., for an incoming DT1 or CODT, for
example.
Authors' Addresses
John Loughney
Nokia Research Center
PO Box 407
FIN-00045 Nokia Group
Finland
EMail: john.Loughney@nokia.com
Greg Sidebottom
Signatus Technologies
Kanata, Ontario
Canada
EMail: greg@signatustechnologies.com
Loughney, et al. Standards Track [Page 129]
RFC 3868 SUA October 2004
Lode Coene
Siemens n.v.
Atealaan 34
B-2200 Herentals
Belgium
Phone: +32-14-252081
EMail: lode.coene@siemens.com
Gery Verwimp
Siemens n.v.
34 Atealaan
PO 2200
Herentals
Belgium
Phone: +32 14 25 3424
EMail: gery.verwimp@siemens.com
Joe Keller
Tekelec
5200 Paramount Parkway
Morrisville, NC 27560
USA
EMail: joe.keller@tekelec.com
Brian Bidulock
OpenSS7 Corporation
1469 Jeffreys Crescent
Edmonton, AB T6L 6T1
Canada
Phone: +1 780 490 1141
EMail: bidulock@openss7.org
Loughney, et al. Standards Track [Page 130]
RFC 3868 SUA October 2004
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Loughney, et al. Standards Track [Page 131]