Middlebox Communications (MIDCOM) Protocol Evaluation
draft-ietf-midcom-protocol-eval-06
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 4097.
|
|
|---|---|---|---|
| Author | Mary Barnes | ||
| Last updated | 2015-10-14 (Latest revision 2002-11-21) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 4097 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Scott O. Bradner | ||
| Send notices to | (None) |
draft-ietf-midcom-protocol-eval-06
Internet Draft M. Barnes
Document: draft-ietf-midcom-protocol-eval-06.txt Editor
Category: Informational Nortel Networks
Expires: May 2003 Nov. 2002
Middlebox Communications (MIDCOM) Protocol Evaluation
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document provides an evaluation of the applicability of SNMP,
RSIP, Megaco, Diameter and COPS as the MIDCOM protocol. A summary
of each of the proposed protocols against the MIDCOM requirements
and the MIDCOM framework is provided. Compliancy of each of the
protocols against each requirement is detailed. A conclusion
summarizes how each of the protocols fares in the evaluation.
Table of Contents
1 Protocol Proposals.............................................2
1.1 SNMP......................................................3
1.2 RSIP......................................................4
1.3 Megaco....................................................6
1.4 Diameter..................................................7
1.5 COPS......................................................8
2 Item Level Compliance Evaluation...............................9
2.1 Protocol machinery........................................9
2.2 Protocol semantics.......................................16
2.3 General Security Requirements............................22
3 Conclusions...................................................24
Security Considerations.........................................25
Normative References............................................25
Informative References..........................................27
Appendix A - SNMP Overview......................................29
Appendix B - RSIP with tunneling................................30
Appendix C - Megaco Modeling Approach...........................31
Appendix D - Diameter IPFilter Rule.............................32
Intellectual Property Statements................................35
Full Copyright Statement........................................35
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Overview
This document provides an evaluation of the applicability of SNMP,
RSIP, Megaco, Diameter and COPS as the MIDCOM protocol. This
evaluation provides overviews of the protocols and general
statements of applicability based upon the MIDCOM framework [2] and
requirements [1] documents.
The process for the protocol evaluation was fairly straightforward
as individuals volunteered to provide an individual draft
evaluating a specific protocol. Thus, some protocols that might be
considered as reasonably applicable as the MIDCOM protocol are not
evaluated in this document since there were no volunteers to
champion the work. The individual protocol documents for which
there were volunteers were submitted for discussion on the list
with feedback being incorporated into an updated draft. The
updated versions of these drafts formed the basis for the content
of this WG document.
Section 1 contains a list of the proposed protocols submitted for
the purposes of the protocol evaluation with some background
information on the protocols and similarities and differences with
regards to the applicability to the framework [2] provided.
Section 2 provides the item level evaluation of the proposed
protocols against the Requirements [1].
Section 3 provides a summary of the evaluation. A table containing
a numerical breakdown for each of the protocols, with regards to
its applicability to the requirements, for the following categories
is provided: Fully met, Partially met through the use of
extensions, Partially met through other changes to the protocol, or
Failing to be met. This summary is not meant to provide a
conclusive statement of the suitability of the protocols, but
rather to provide information to be considered as input into the
overall protocol decision process.
In order for this document to serve as a complete evaluation of the
protocols, some of the background information and more detailed
aspects of the proposals documenting enhancements and applications
of the protocols to comply with the MIDCOM framework and
requirements are included in Appendices.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [4].
1 Protocol Proposals
The following protocols were submitted to the MIDCOM WG for
consideration:
o SNMP
o RSIP
o Megaco
o Diameter
o COPS
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The following provides an overview of each of the protocols and the
applicability of each protocol to the MIDCOM framework.
1.1 SNMP
This section provides a general statement with regards to the
applicability of SNMP as the MIDCOM protocol. A general overview
and some specific details of SNMP are provided in Appendix A. This
evaluation of SNMP is specific to SNMPv3, which provides the
security required for MIDCOM usage. SNMPv1 and SNMPv2c would be
inappropriate for MIDCOM since they have been declared Historic,
and because their messages have only trivial security. Some
specifics with regards to existing support for NAT and Firewall
Control are provided in section 1.1.2. The differences between the
SNMP framework and the MIDCOM framework are addressed in section
1.1.3.
1.1.1 SNMP General Applicability
The primary advantages of SNMPv3 are that it is a mature, well
understood protocol, currently deployed in various scenarios, with
mature toolsets available for SNMP managers and agents.
Application intelligence is captured in MIB modules, rather than in
the messaging protocol. MIB modules define a data model of the
information that can be collected and configured for a managed
functionality. The SNMP messaging protocol transports the data in a
standardized format without needing to understand the semantics of
the data being transferred. The endpoints of the communication
understand the semantics of the data.
Partly due to the lack of security in SNMPv1 and SNMPv2c, and
partly due to variations in configuration requirements across
vendors, few MIB modules have been developed that enable
standardized configuration of managed devices across vendors. Since
monitoring can be done using only a least-common-denominator subset
of information across vendors, many MIB modules have been developed
to provide standardized monitoring of managed devices. As a result,
SNMP has been used primarily for monitoring rather than for
configuring network nodes.
SNMPv3 builds upon the design of widely-deployed SNMPv1 and SNMPv2c
versions. Specifically, SNMPv3 shares the separation of data
modeling (MIBs) from the protocol to transfer data, so all existing
MIBs can be used with SNMPv3. SNMPv3 also uses the SMIv2 standard,
and it shares operations and transport with SNMPv2c. The major
difference between SNMPv3 and earlier versions is the addition of
strong message security and controlled access to data.
SNMPv3 uses the architecture detailed in RFC2571, where all SNMP
entities are capable of performing certain functions, such as the
generation of requests, response to requests, the generation of
asynchronous notifications, the receipt of notifications, and the
proxy-forwarding of SNMP messages. SNMP is used to read and
manipulate virtual databases of managed-application-specific
operational parameters and statistics, which are defined in MIB
modules.
1.1.2 SNMP Existing Support for NAT and Firewall Control
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For configuring NATs, there is currently a NAT MIB module [NAT-MIB]
under development. The NAT MIB module meets all of the MIDCOM
requirements concerning NAT control with the exception of grouping
of policy rules (requirement 2.2.3.). In order to support this, an
additional grouping table in the NAT MIB module is required.
Existing work for firewall control with SNMP only considered the
monitoring of firewalls and not the configuration. Further work is
required towards the development of MIBs for configuring firewalls.
1.1.3 Architectural Differences between SNMP and MIDCOM
The SNMP management framework provides functions equivalent to
those defined by the MIDCOM framework, although there are a few
architectural differences.
Traditionally, SNMP entities have been called Manager and Agent.
Manager and agent are now recognized as entities designed to
support particular configurations of SNMPv3 functions. A
traditional manager is an entity capable of generating requests and
receiving notifications, and a traditional agent is an entity
capable of responding to requests and generating notifications.
The SNMP use of the term agent is different from its use in the
MIDCOM framework: The SNMP Manager corresponds to the MIDCOM agent
and the SNMP Agent corresponds to the MIDCOM PDP. The SNMP
evaluation assumes that the MIDCOM PDP (SNMP Agent) is physically
part of the middlebox, which is allowed by the MIDCOM framework as
described in section 6.0 of [2]. Thus, for the purpose of this
evaluation, the SNMP agent corresponds to the Middlebox.
While this evaluation is based on the assumption that the SNMP
agent corresponds to the middlebox, SNMP does not force such a
restriction.
Proxy means many things to many people. SNMP can be deployed using
intermediate entities to forward messages, or to help distribute
policies to the middlebox, similar to the proxy capabilities of the
other candidate protocols. Since proxy adds configuration and
deployment complexity and is not necessary to meet the specified
MIDCOM requirements, the use of a proxy agent or mid-level manager
is not considered in this evaluation. Further details on SNMP proxy
capabilities are provided in Appendix A.
Although the SNMP management framework does not have the concept of
a session, session-like associations can be established through the
use of managed objects. In order to implement the MIDCOM protocol
based on SNMP, a MIDCOM MIB module is required. All requests from
the MIDCOM agent to the Middlebox would be performed using write
access to managed objects defined in the MIDCOM MIB module. Replies
to requests are signaled by the Middlebox (SNMP agent), by
modifying the managed objects. The MIDCOM agent (SNMP manager) can
receive this information by reading or polling, if required, the
corresponding managed object.
1.2 RSIP
1.2.1 Framework elements in common to MIDCOM and RSIP
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The following framework elements are common to MIDCOM and RSIP
listed by their MIDCOM names, with the RSIP name indicated in
parenthesis:
o Hosts
o Applications
o Middleboxes (RSIP gateways)
o Private domain (private realm)
o External domain (public realm)
o Middlebox communication protocol (RSIP)
o MIDCOM agent registration (host registration)
o MIDCOM session (RSIP session)
o MIDCOM Filter (local / remote address and port number(s) pairs)
1.2.2 MIDCOM Framework elements not supported by RSIP
The following MIDCOM framework elements are not supported by RSIP:
o Policy actions and rules. RSIP always implicitly assumes a
permit action. To support MIDCOM, a more general and explicit
action parameter would have to be defined. RSIP requests
specifying local / remote address and port number(s) pairs would
have to be extended to include an action parameter, in MIDCOM
rules.
o MIDCOM agents. RSIP makes no distinction between applications
and agents; address assignment operations can be performed
equally by applications and agents.
o Policy Decision Points. RSIP assumes that middleboxes grant or
deny requests with reference to a policy known to them; the
policy could be determined jointly by the middlebox and a policy
decision point; such joint determination is not addressed by the
RSIP framework, nor is it specifically precluded.
1.2.3 RSIP Framework elements not supported by MIDCOM
The following elements are unique to the RSIP framework. If RSIP
were adopted as the basis for the MIDCOM protocol, they could be
added to the MIDCOM framework:
o RSIP client: that portion of the application (or agent) that
talks to the RSIP gateway using RSIP.
o RSIP server: that portion of an RSIP gateway that talks to
applications using RSIP.
o Realm Specific Address IP (RSA-IP) and Realm Specific Address and
Port IP (RSAP-IP): RSIP distinguishes between filters that
include all ports on an IP address and those that do not.
o Demultiplexing Fields: Any set of packet header or payload fields
that an RSIP gateway uses to route an incoming packet to an RSIP
host. RSIP allows a gateway to perform, and an application to
control, packet routing to hosts in the private domain based on
more than IP header fields.
o Host-to-middlebox tunnels: RSIP assumes that data communicated
between a private realm host and a public realm host is
transferred through the private realm by a tunnel between the
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inner host and the middle box, where it is converted to and from
native IP based communications to the public realm host.
1.2.4. Comparison of MIDCOM and RSIP frameworks
RSIP with tunneling, has the advantage that the public realm IP
addresses and port numbers are known to the private realm host
application, thus no translation is needed for protocols such as
SDP, the FTP control protocol, RTSP, SMIL, etc.. However, this does
require that an RSIP server and a tunneling protocol be implemented
in the middlebox and an RSIP client and the tunneling protocol be
implemented in the private realm host. The host modifications can
generally be made without modification to the host application or
requiring the implementation of a host application agent. This is
viewed as a significant advantage over NAT (Network Address
Translation).
Further details on the evaluation of RSIP with regards to tunneling
in the context of NAT support are available in Appendix B of this
document.
1.3 Megaco
1.3.1 Megaco Architectural Model
Megaco is a master-slave, transaction-oriented protocol in which
Media Gateway Controllers (MGC) control the operation of Media
Gateways (MG). Originally designed to control IP Telephony
gateways, it is used between an application-unaware device (the
Media Gateway) and an intelligent entity (the Media Gateway
Controller) having application awareness.
The Megaco model includes the following key concepts:
1. Terminations: Logical entities on the MG that act as sources or
sink of packet streams. A termination can be physical or ephemeral
and is associated with a single MGC.
2. Context: An association between Terminations for sharing media
between the Terminations. Terminations can be added, subtracted
from a Context and can be moved from one Context to another. A
Context and all of its Terminations are associated with a single
MGC.
3. Virtual Media Gateways: A physical MG can be partitioned into
multiple virtual MGs allowing multiple Controllers to interact with
disjoint sets of Contexts/Terminations within a single physical
device.
4. Transactions/Messages: Each Megaco command applies to one
Termination within a Context and generates a unique response.
Commands may be replicated implicitly so that they act on all
Terminations of a given Context through wildcarding of Termination
identifiers. Multiple commands addressed to different Contexts can
be grouped in a Transaction structure. Similarly, multiple
Transactions can be concatenated into a Message.
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5. Descriptors/Properties: A Termination is described by a number
of characterizing parameters or Properties, which are grouped in a
set of Descriptors that are included in commands and responses.
6. Events and signals: A Termination can be programmed to perform
certain actions or to detect certain events and notify the Agent.
7. Packages: Packages are groups of properties, events, etc.
associated with a Termination. Packages are simple means of
extending the protocol to serve various types of devices or
Middleboxes.
1.3.2 Comparison of the Megaco and MIDCOM Architectural Frameworks
In the MIDCOM architecture, the Middlebox plays the role of an
application-unaware device being controlled by the application-
aware Agent. In the Megaco architecture, the Media Gateway
controller serves a role similar to the the MIDCOM Agent (MA) and
the Media Gateway serves a role similar to the Middlebox (MB). One
major difference between the Megaco model and the MIDCOM protocol
requirements is that MIDCOM requires that the MIDCOM Agent
establish the session. Whereas, the Megaco definition is that a MG
(Middlebox) establishes communication with an MGC (MIDCOM Agent).
1.4 Diameter
1.4.1 Diameter Architecture
Diameter is designed to support AAA for network access. It is
meant to operate through networks of Diameter nodes, which both act
upon and route messages toward their final destinations. Endpoints
are characterized as either clients, which perform network access
control, or servers, which handle authentication, authorization and
accounting requests for a particular realm. Intermediate nodes
perform relay, proxy, redirect, and translation services. Design
requirements for the protocol [29] include robustness in the face
of bursty message loads and server failures, resistance to specific
DOS attacks and protection of message contents, and extensibility
including support for vendor-specific attributes and message types.
The protocol is designed as a base protocol to be supported by all
implementations, plus extensions devoted to specific applications.
Messages consist of a header and an aggregation of "Attribute-Value
Pairs (AVPs)", each of which is a tag-length-value construct. The
header includes a command code, which determines the processing of
the message and what other AVP types must or may be present. AVPs
are strongly typed. Some basic and compound types are provided by
the base protocol specification, while others may be added by
application extensions. One of the types provided in the base is
the IPFilterRule, which may be sufficient to express the Policy
Rules that MIDCOM deals with.
Messaging takes the form of request-answer exchanges. Some
exchanges may take multiple round-trips to complete. The protocol
is connection-oriented at both the transport and application
levels. In addition, the protocol is tied closely to the idea of
sessions, which relate sequences of message exchanges through use
of a common session identifier. Each application provides its own
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definition of the semantics of a session. Multiple sessions may be
open simultaneously.
1.4.2 Comparison of Diameter With MIDCOM Architectural Requirements
The MIDCOM Agent does not perform the functions of a Diameter
client, nor does the Middlebox support the functions of a Diameter
server. Thus the MIDCOM application would introduce two new types
of endpoints into the Diameter architecture. Moreover, the MIDCOM
requirements do not at this time imply any type of intermediate
node.
A general assessment might be that Diameter meets and exceeds
MIDCOM architectural requirements, however the connection
orientation may be too heavy for the number of relationships the
Middlebox must support. Certainly the focus on extensibility,
request-response messaging orientation, and treatment of the
session, are all well-matched to what MIDCOM needs. At this point,
MIDCOM is focused on simple point-to-point relationships, so the
proxying and forwarding capabilities provided by Diameter are not
needed. Most of the commands and AVPs defined in the base protocol
are also surplus to MIDCOM requirements.
1.5 COPS
Overall, COPS and COPS-PR have similar compliancy with regards to
the MIDCOM protocol requirements. In this document, references to
COPS are generally applicable to both COPS and COPS-PR. However,
COPS-PR is explicitly identified to meet two of the requirements.
The only other major difference between COPS-PR and COPS, as
applied to the MIDCOM protocol, would be the description of the
MIDCOM policy rule attributes with COPS-PR MIDCOM PIB attributes
rather than COPS MIDCOM client specific objects.
1.5.1 COPS protocol architecture
COPS is a simple query and response protocol that can be used to
exchange policy information between a policy server (Policy
Decision Point or PDP) and its clients (Policy Enforcement Points
or PEPs). COPS was defined to be a simple and extensible protocol.
The main characteristics of COPS include the following:
1. The protocol employs a client/server model. The PEP sends
requests, updates, and deletions to the remote PDP and the PDP
returns decisions back to the PEP.
2. The protocol uses TCP as its transport protocol for reliable
exchange of messages between policy clients and a server.
3. The protocol is extensible in that it is designed to leverage
self-identifying objects and can support diverse client specific
information without requiring modification of the COPS protocol.
4. The protocol was created for the general administration,
configuration, and enforcement of policies.
5. COPS provides message level security for authentication, replay
protection, and message integrity. COPS can make use of existing
protocols for security such as IPSEC [IPSEC] or TLS to authenticate
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and secure the channel between the PEP and the PDP.
6. The protocol is stateful in two main aspects:
(1) Request/Decision state is shared and kept synchronized in a
transactional manner between client and server. Requests from the
client PEP are installed or remembered by the remote PDP until they
are explicitly deleted by the PEP. At the same time, Decisions from
the remote PDP can be generated asynchronously at any time for a
currently installed request state.
(2) State from various events (Request/Decision pairs) may be
inter-associated. The server may respond to new queries differently
because of previously installed, related Request/Decision state(s).
7. The protocol is also stateful in that it allows the server to
push configuration information to the client, and then allows the
server to remove such state from the client when it is no longer
applicable.
1.5.2 Comparison of COPS and the MIDCOM Framework
In the MIDCOM framework, the Middlebox enforces the policy
controlled by an application-aware Agent. Thus, when compared to
the COPS architecture, the Middlebox serves as the PEP (COPS
Client) and the MIDCOM Agent serves as the PDP (COPS Policy
Server). One major difference between the COPS protocol model and
the MIDCOM protocol requirements is that MIDCOM requires that the
MIDCOM Agent establish the session. Whereas, the COPS definition
is that a PEP (Middlebox) establishes communication with a PDP
(MIDCOM Agent).
2 Item Level Compliance Evaluation
This section contains a review of the protocol's level of
compliance to each of the MIDCOM Requirements [1]. The following
key will be used to identify the level of compliancy of each of the
individual protocols:
T = Total Compliance. Meets the requirement fully.
P+ = Partial Compliance+. Fundamentally meets the requirement
through the use of extensions (e.g. packages, additional
parameters, etc).
P = Partial Compliance. Meets some aspect of the requirement,
however, the necessary changes require more than an extension
and/or are inconsistent with the design intent of the
protocol.
F = Failed Compliance. Does not meet the requirement.
2.1 Protocol machinery
This section describes the compliancy of the proposed protocols
against the protocol machinery requirements from section 2.1 of the
requirements document [1]. A short description of each of the
protocols is provided to substantiate the evaluation.
2.1.1 Ability to establish association between Agent and Middlebox.
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SNMP: T, RSIP: P+, Megaco: P, Diameter: T, COPS: P
SNMP: SNMPv3 provides mutual authentication at the user level
(where the user can be an application or a host if desired) via
shared secrets. Each authenticated principal is associated with a
group that has access rights that control the principalÆs ability
to perform operations on specific subsets of data. Failure to
authenticate can generate a SNMP notification (administrator
configurable choice).
RSIP: RSIP allows sessions to be established between middleboxes
and applications and MIDCOM agents. Authorization credentials would
have to be added to the session establishment request to allow the
middlebox to authorize the session requestor.
Megaco: There is a directionality component implicit in this
requirement in that the MA initiates the establishment
of the authorized session. Megaco defines this association to
be established in the opposite direction, i.e., the Middlebox(MG)
initiates the establishment. If this restriction is not considered,
then Megaco makes the syntax and semantics available for the
endpoint to initiate the connection.
Diameter: Although this is out of scope, the Diameter specification
describes several ways to discover a peer. Having done so, a
Diameter node establishes a transport connection (TCP, TLS, or
SCTP) to the peer. The two peers then exchange Capability Exchange
Request/Answer messages to identify each other and determine the
Diameter applications each supports.
If the connection between two peers is lost, Diameter prescribes
procedures whereby it may be re-established. To ensure that loss
of connectivity is detected quickly, Diameter provides the Device-
Watchdog Request/Answer messages, to be used when traffic between
the two peers is low.
Diameter provides an extensive state machine to govern the
relationship between two peers.
COPS: COPS does not meet the directionality part of the
requirement. The definition of COPS allows a PEP (Middlebox) to
establish communication with a PDP (MIDCOM Agent). However, nothing
explicitly prohibits a PDP from establishing communication with a
PEP. The PEP could have local policies dictating what action to
take when it is contacted by an unknown PDP. These actions, defined
in the local policies, would ensure the proper establishment of an
authorized association.
2.1.2 Agent can relate to multiple Middleboxes
SNMP: T, RSIP: P, Megaco: T, Diameter: T, COPS: T
SNMP: An SNMP manager can communicate simultaneously with several
Middleboxes.
RSIP: RSIP sessions are identified by their IP source and
destination addresses and their TCP / UDP port numbers. Thus each
RSIP client can communicate with multiple servers, and each server
can communicate with multiple clients. However, RSIP did not
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explicitly include agents in its design. The architecture and
semantics of RSIP messages do not preclude agents, thus the RSIP
architecture could certainly be extended to explicitly include
agents; therefore RSIP is deemed partially compliant to this
requirement.
Megaco: Megaco allows an MA to control several Middle Boxes. Each
message carries an identifier of the endpoint that transmitted the
message allowing the recipient to determine the source.
Diameter: Diameter allows connection to more than one peer (and
encourages this for improved reliability). Whether the Diameter
connection state machine is too heavy to support the number of
connections needed is a matter for discussion.
COPS: COPS PDPs are designed to communicate with several PEPs.
2.1.3 Middlebox can relate to multiple Agents
SNMP: T, RSIP: P, Megaco: T, Diameter: T, COPS: T
SNMP: An SNMP agent can communicate with several SNMP managers
Simultaneously.
RSIP: Refer to 2.1.2.
Megaco: Megaco has the concept of Virtual Media Gateways (VMG),
allowing multiple MGCs to communicate simultaneously with the same
MG. Applying this model to MIDCOM would allow the same middlebox
(MG) to have associations with multiple MIDCOM Agents (MGCs).
Diameter: Diameter allows connection to more than one peer and
encourages this for improved reliability. Whether the Diameter
connection state machine is too heavy to support the number of
connections needed is a matter for discussion. The Middlebox and
Agent play symmetric roles as far as Diameter peering is concerned.
COPS: The COPS-PR framework specifies that a PEP should have a
unique PDP in order to achieve effective policy control. The COPS-
PR protocol would allow the scenario whereby a PEP establishes
communication with multiple PDPs by creating a COPS client instance
per PDP.
2.1.4 Deterministic outcome when multiple requests are presented to
the Middlebox simultaneously
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: While the architectural design of SNMP can permit race
conditions to occur, there are mechanisms defined as part of the
SNMPv3 standard, such as view-based access control and advisory
locking that can be used to prevent the conditions, and MIB modules
may also contain special functionality, such as RMONÆs OwnerString,
to prevent conflicts. Deterministic behavior of SNMP agents when
being accessed by multiple managers is important for several
management applications and supported by SNMP.
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RSIP: All RSIP requests are defined to be atomic. Near simultaneous
requests are executed as is they were sequential.
Megaco: Megaco supports the concept of VMGs to make these
interactions deterministic and to avoid resource access conflicts.
Each VMG has a single owner, in a MGC, and there can be no overlap
between the sets of Terminations belonging to multiple VMGs. The
Megaco protocol messages also include the identifier of the sending
entity, so that the MG can easily determine to whom to send the
response or asynchronously report certain events.
Diameter: Diameter depends partly upon the transport protocol to
provide flow control when the server becomes heavily loaded. It
also has application-layer messaging to indicate that it is too
busy or out of space (Diameter_TOO_BUSY and Diameter_OUT_OF_SPACE
result codes).
COPS: COPS has built-in support for clear state and policy
instances. This would allow the creation of well-behaved MIDCOM
state machines.
2.1.5 Known and stable state
SNMP: T, RSIP: T, Megaco: T, Diameter: P, COPS: T
SNMP: Requests are atomic in SNMP. MIB modules can define which
data is persistent across reboots, so a known startup state can be
established. The manager can poll the agent to determine the
current state.
RSIP: RSIP assumes that on middlebox start-up no sessions are
defined, and thus no allocations have been made. In effect, all
resources are released upon restart after failure.
Megaco: Megaco has extensive audit capabilities to synchronize
states between the MG and the MGC. Megaco also provides the
MGC with the ability to do mass resets, as well as individual
resets. The MGC can always release resources in the MG. The MG can
also initiate the release of resources by the MGC.
Diameter: Diameter documentation does not discuss the degree of
atomicity of message processing, so this would have to be specified
in the MIDCOM extension.
COPS: The COPS protocol maintains synchronized states between
Middleboxes and MA hence all the states are known on both sides.
2.1.6 Middlebox status report
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: The status of a middlebox can be reported using asynchronous
communications, or via polling.
RSIP: All RSIP client requests have explicit server responses.
Additionally, a client may explicitly request server status using
a QUERY request.
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Megaco: Megaco has extensive audit capabilities for the MG to
report status information to the MGC. It can also report some
status updates using the ServiceChange command.
Diameter: Diameter provides a number of response codes by means of
which a server can indicate error conditions reflecting status of
the server as a whole. The Disconnect-Peer-Request provides a
means in the extreme case to terminate a connection with a peer
gracefully, informing the other end about the reason for the
disconnection.
COPS: The COPS Report message is designed to indicate any
asynchronous conditions/events.
2.1.7 Middlebox can generate unsolicited messages
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: SNMPv3 supports both confirmed and unconfirmed asynchronous
notifications.
RSIP: An RSIP server will send an unsolicited DE_REGISTER_RESPONSE
to force an RSIP host to relinquish all of its bindings and
terminate its relationship with the RSIP gateway. An RSIP server
can send an asynchronous ERROR_RESPONSE to indicate less severe
conditions.
Megaco: Megaco supports the asynchronous notification of events
using the Notify command.
Diameter: The Diameter protocol permits either peer in a connection
to originate transactions. Thus the protocol supports Middlebox-
originated messages.
COPS: The COPS Report message is designed to indicate any
asynchronous conditions/events.
2.1.8 Mutual authentication
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: SNMPv3 meets this requirement. SNMPv3 supports user
authentication and explicitly supports symmetric secret key
encryption between MIDCOM agent (SNMP manager) and Middlebox (SNMP
agent), thus supporting mutual authentication. The default
authentication and encryption methods are specified in RFC 2574
(MD5, SHA-1, and DES). Different users at the same management
application (MIDCOM agent) can authenticate themselves with
different authentication and encryption methods, and additional
methods can be added to SNMPv3 entities as needed.
RSIP: This requirement can be met by operating RSIP over IPSec. The
RSIP framework recommends all communication between an RSIP host
and gateway be authenticated. Authentication, in the form of a
message hash appended to the end of each RSIP protocol packet, can
serve to authenticate the RSIP host and gateway to one another,
provide message integrity, and avoid replay attacks with an anti-
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replay counter. However, the message hash and replay counter
parameters would need to be defined for the RSIP protocol.
Megaco: Megaco provides for the use of IPSec for all security
mechanisms including mutual authentication, integrity check and
encryption. Use of IKE is recommended with support of RSA
signatures and public key encryption.
Diameter: The Diameter base protocol assumes that messages are
secured by using either IPSec or TLS. Diameter requires that when
using the latter, peers must mutually authenticate themselves.
COPS: COPS has built-in message level security for authentication,
replay protection, and message integrity. COPS can also use TLS or
IPSec.
2.1.9 Termination of session by either party
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: Each SNMPv3 message is authenticated and authorized, so each
message could be considered to have its own session, which
automatically terminates after processing. Processing may be
stopped for a number of reasons, such as security, and a response
is sent.
Either peer may stop operating, and be unavailable for further
operations. The authentication and/or authorization parameters of a
principal may be changed between operations if desired, to prevent
further authentication or authorization for security reasons.
Additionally, managed objects can be defined for realizing sessions
that persist beyond processing of a single message. The MIB module
would need to specify the responsibility for cleanup of the objects
following normal/abnormal termination.
RSIP: An RSIP client may terminate a session with a
DE_REGISTER_REQUEST. An RSIP server may terminate a session with an
unsolicited DE_REGISTER_RESPONSE, and then respond to subsequent
requests on the session with a REGISTER_FIRST error.
Megaco: The Megaco protocol allows both peers to terminate the
association with proper reason code.
Diameter: Either peer in a connection may issue a Disconnect-Peer-
Request to end the connection gracefully.
COPS: COPS allows both the PEP and PDP to terminate a session.
2.1.10 Indication of success or failure
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: Each operation request has a corresponding response message
that contains an error status to indicate success or failure. For
complex requests that the middlebox cannot complete immediately,
the corresponding MIB module may be designed to also provide
asynchronous notifications of the success or failure of the
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complete transaction, and/or may provide pollable objects that
indicate the success or failure of the complete transaction. For
example, see ifAdminStatus and ifOperStatus in RFC2863 [33].
RSIP: All RSIP requests result in a paired RSIP response if the
request was successful or an ERROR_RESPONSE if the request was not
successful.
Megaco: Megaco defines a special descriptor called an Error
descriptor that contains the error code and an optional explanatory
string.
Diameter: Every Diameter request is matched by a response, and this
response contains a result code as well as other information.
COPS: The COPS Report message directly fulfills this requirement.
2.1.11 Version interworking
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: SNMP has a separation of the protocol to carry data, and the
data that defines additional management functionality. Additional
functionality can be added easily through MIBs. Capability exchange
in SNMP is usually uni-directional. Managers can query the
middlebox (SNMP agent) to determine which MIBs are supported. In
addition, multiple message versions can be supported
simultaneously, and are identified by a version number in the
message header.
RSIP: Each RSIP message contains a version parameter.
Megaco: Version interworking and negotiation are supported both for
the protocol and any extension Packages.
Diameter: The Capabilities Exchange Request/Answer allows two peers
to determine information about what each supports, including
protocol version and specific applications.
COPS: The COPS protocol can carry a MIDCOM version number and
capability negotiation between the COPS client and the COPS server.
This capability negotiation mechanism allows the COPS client and
server to communicate the supported features/capabilities. This
would allow seamless version interworking.
2.1.12 Deterministic behaviour in the presence of overlapping
rules
SNMP: T, RSIP: T, Megaco: P, Diameter: T, COPS: T
SNMP: Rulesets would be defined in MIBs. The priority of rulesets,
and the resolution of conflict, can be defined in the MIB module
definition. The SNMPConf policy MIB defines mechanisms to achieve
deterministic behavior in the presence of overlapping rule sets.
RSIP: All requests for allocation of IP addresses, or ports or both
resulting in rule overlap are rejected by an RSIP server with a
LOCAL_ADDR_INUSE error.
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Megaco: This is met with the help of a model that separates Megaco
protocol elements from the overlapping Policy rules (see
Appendix C). However, new behavior for the Megaco protocol elements
needs to be specified as part of a new MIDCOM specific Package.
Diameter: The IPFilterRule type specification, which would probably
be used as the type of a Policy Rule AVP, comes with an extensive
semantic description providing a deterministic outcome, which the
individual Agent cannot know unless it knows all of the Policy
Rules installed on the Middlebox. Rules for the appropriate
direction are evaluated in order, with the first matched rule
terminating the evaluation. Each packet is evaluated once. If no
rule matches, the packet is dropped if the last rule evaluated was
a permit, and passed if the last rule was a deny. The IPFilterRule
format and further details on its applicability to this requirement
are provided in Appendix D.
COPS: The COPS protocol provides transactional-based communication
between the PEP and PDP, hence the behavior is totally
deterministic provided the middlebox state machine is designed
correctly. The COPS protocol features encourage and support good
state machine design.
2.2 Protocol semantics
This section contains the individual protocols as evaluated against
the protocol semantic requirements from section 2.2 of the
requirements document [1]. A short description of each of the
protocols is provided to substantiate the evaluation.
2.2.1 Extensibility
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: Extensibility is a basic feature of the SNMP management
Framework.
RSIP: All RSIP messages consist of three mandatory fields (protocol
version, message type, and message length) and a sequence of
parameterType / length / value 3-tuples. New messages may be
defined by defining new values for the message type field. New
parameter types may be defined, and existing messages may be
extended, by defining new parameterType values. If new messages,
parameters, or both are added in a non-backward compatible way, a
new value of the protocol version field may be defined. This may
be desirable even of the additions are backward compatible.
Megaco: Megaco is easily extensible through new Packages, which
allow definition of new attributes and behavior of a Termination.
Diameter: Diameter provides a great deal of flexibility for
extensions, including allowance for vendor-defined commands and
AVPs and the ability to flag each AVP as must-understand or
ignorable if not understood.
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COPS: The COPS protocol is extensible, since it was designed to
separate the Protocol from the Policy Control Information.
2.2.2 Support of multiple Middlebox types
SNMP: T, RSIP: P+, Megaco: T, Diameter: P+, COPS: T
SNMP: SNMP explicitly supports managing different device types with
different capabilities. First the managed object called sysObjectID
from basic MIB-II [3] identifies the type of box. For boxes with
variable capabilities, SNMP can check the availability of
corresponding MIBs.
RSIP: All types of middleboxes are supported so long as the ruleset
action is permit. Other actions would require the definition of a
new RSIP message parameter with values for permit and the other
desired actions.
Megaco: Megaco can support multiple Middlebox types on the same
interface either by designing the properties representing the
Policy Rules to provide this support, or by using multiple
terminations in the same session, each representing one type of
action. In the latter case, the Megaco Context can be used as a
convenient means of managing the related terminations as a group.
However, the inherent idea of flow between terminations of a
context is irrelevant and would have to be discarded.
Diameter: Any necessary additional AVPs or values must be specified
as part of the MIDCOM application extension (see <2.2.8> below).
COPS: COPS allows a PDP to provide filters and actions to multiple
PEP functions through a single COPS session.
2.2.3 Ruleset groups
SNMP: T, RSIP: P+, Megaco: T, Diameter: T, COPS: T
SNMP: This requirement can be realized via the SNMP management
framework by an appropriate definition of a MIB module. The
SNMPConf WG has already defined an SNMP Policy MIB that permits the
definitions of policy rulesets and grouping of rulesets.
RSIP: RSIP currently only allows one IP address, or address and
port range, to be assigned to a bind-ID. RSIP could implement
rulesets as required by adding an optional bind-ID parameter to the
ASSIGN_REQUESTs to extend an existing ruleset rather than creating
a new one. Similarly, the FREE_REQUESTs would have to be extended
by adding optional, local and remote, address and port parameters.
Megaco: The Megaco context can be used to group terminations to be
managed together. For example, all of the terminations, each
representing an instantiation of a Policy Rule, can be deleted in
one command by doing a wildcarded Subtract from the context.
However, the inherent idea of media flows between terminations of a
context would be irrelevant in this application of the protocol.
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Diameter: Diameter allows message syntax definitions where multiple
instances of the same AVP (for example, a Policy Rule AVP whose
syntax and low-level semantics are defined by the IPFilterRule type
definition) may be present. If a tighter grouping is required, the
set of Diameter base types includes the Grouped type. MIDCOM can
choose how to make use of these capabilities to meet the ruleset
group requirement when defining its application extension to the
Diameter protocol.
COPS: The COPS-PR Handle State may be used to associate the set of
closely related policy objects. As the Middlebox learns additional
requirements, the Middlebox adds these resource requirements under
the same handle ID, which constitutes the required aggregation.
2.2.4 Lifetime extension
SNMP: P+, RSIP: T, Megaco: T, Diameter: T, COPS: P+
SNMP: This requirement can be realized via the SNMP management
framework by an appropriate definition of a MIB module. The
SNMPConf WG has developed a Policy MIB module that includes a
pmPolicySchedule object with a modifiable lifetime.
RSIP: A client may request an explicit lease time when a request is
made to assign one or more IP addresses, ports or both. The server
may grant the requested lease time, or assign one if none was
requested. Subsequently, the lease time may be extended if a
client's EXTEND_REQUEST is granted by the server.
Megaco: The MG can report the imminent expiry of a policy rule to
the MGC, which can then extend or delete the corresponding
Termination.
Diameter: The Diameter concept of a session includes the session
lifetime, grace period, and lifetime extension. It may make sense
to associate the Diameter session with the lifetime of a MIDCOM
Policy Rule, in which case support for lifetime extension comes
ready-made.
COPS: COPS allows a PDP to send unsolicited decisions to the PEP.
However, the unsolicited events will be relevant to the COPS MIDCOM
specific client or the MIDCOM specific PIB which needs to be
defined. This would allow the PDP to extend the lifetime of an
existing ruleset.
2.2.5 Handling of Mandatory/optional nature of unknown attributes
SNMP: T, RSIP: T, Megaco: P+, Diameter: P+, COPS: T
SNMP: Unknown attributes in a read operation are flagged as
exceptions in the Response message, but the rest of the read
succeeds. In a write operation (a SET request), all attributes are
validated before the write is performed. If there are unknown
attributes, the request fails and no writes are done. Unknown
attributes are flagged as exceptions in the Response message, and
the error status is reported.
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RSIP: All options of all requests are fully specified. Not
understood parameters must be reported by an ERROR_RESPONSE with an
EXTRA_PARM error value, with the entire request otherwise ignored.
Megaco: Megaco entities provide Error codes in response messages.
If a command marked "Optional" in a transaction fails, the
remaining commands will continue. However, the specified
requirement deals with rules of processing properties that need
definition in new Package.
Diameter: Indication of the mandatory or optional status of AVPs is
fully supported, provided it is enabled in the AVP definition. No
guidance is imposed regarding the return of diagnostic information
for optional AVPs.
COPS: COPS provides for the exchange of capabilities and
limitations between the PEP and PDP to ensure well-known outcomes
are understood for scenarios with unknown attributes. There is also
clear error handling for situations when the request is rejected.
2.2.6 Actionable failure reasons
SNMP: T, RSIP: P+, Megaco: T, Diameter: T, COPS: T
SNMP: The SNMPv3 protocol returns error codes and exception codes
in Response messages, to permit the requestor to modify their
request. Errors and exceptions indicate the attribute that caused
the error, and an error code identifies the nature of the error
encountered.
If desired, a MIB can be designed to provide additional data about
error conditions either via asynchronous notifications or polled
objects.
RSIP: RSIP defines a fairly large number of very specific error
values. It is anticipated that additional error values will also
have to be defined along with the new messages and parameters
required for MIDCOM.
Megaco: The MG can provide Error codes in response messages
allowing the MGC to modify its behavior. Megaco uses transaction
identifiers for correlation between a response and a command. If
the same transaction id is received more than once, the receiving
entity silently discards the message, thus providing some
protection against replay attacks.
Diameter: Diameter provides an extensive set of failure reasons in
the base protocol.
COPS: COPS uses an error object to identify a particular COPS
protocol error. The error sub-code field may contain additional
detailed COPS client (MIDCOM Middlebox) specific error codes.
2.2.7 Multiple Agents operating on the same ruleset.
SNMP: T, RSIP: P, Megaco: P, Diameter: T, COPS: P
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SNMP: The SNMP framework supports multiple managers working on the
same managed objects. The View-based Access Control Model (VACM,
[RFC2575]) even offers means to customize the access rights of
different managers in a fine-grained way.
RSIP: RSIP neither explicitly permits nor precludes an operation on
a binding by a host that had not originally create the binding.
However, to support this requirement, the RSIP semantics must be
extended to explicitly permit any authorized host to request
operations on a binding; this does not require a change to the
protocol.
Megaco: If the Megaco state machine on the Middle Box is decoupled
from the Middle Box policy rule management, this requirement can be
met with local policies on the Middle Box. However, this violates
the spirit of the Megaco protocol, thus Megaco is considered
partially compliant to this requirement.
Diameter: The Diameter protocol, as currently defined, would allow
multiple agents to operate on the same ruleset.
COPS: It is possible to use COPS to operate the same resource with
multiple agents. An underlying resource management function,
separate from the COPS state machine, on the Middlebox will handle
the arbitration when resource conflicts happen.
2.2.8 Transport of filtering rules
SNMP: P+, RSIP: P+, Megaco: P+, Diameter: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
MIDCOM MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: To support this requirement, a new optional enumeration
parameter, transportProtocol, can be added to the RSIP
ASSIGN_REQUESTs. When the parameter is included, the binding
created applies only to the use of the bound addresses and ports,
by the specific transportProtocol. When the parameter is not
included, the binding applies to the use of all the bound addresses
and ports, by any transport protocol, thus maintaining backward
compatibility with the current definition of RSIP.
Megaco: Megaco protocol can meet this requirement by defining a new
property for the transport of filtering rules.
Diameter: While Diameter defines the promising IPFilterRule data
type (see 2.1.12 above), there is no existing message, which would
convey this to a Middlebox along with other required MIDCOM
attributes. A new MIDCOM application extension of Diameter would
have to be defined.
COPS: The COPS protocol can meet this requirement by using a COPS
MIDCOM specific client or a MIDCOM specific PIB.
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2.2.9 Mapped port parity
SNMP: P+, RSIP: P+, Megaco: P+, Diameter: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
MIDCOM MIB module.
RSIP: To support this requirement, a new optional boolean
parameter, portOddity, can be added to the RSIP ASSIGN_REQUESTs.
If the parameter is TRUE, the remote port number of the binding
created would have the same oddity as the local port. If the
parameter is not specified, or is FALSE, the remote port's oddity
is independent of the local port's oddity, thus maintaining
backward compatibility with the current definition of RSIP.
Megaco: Megaco can be easily extended using a MIDCOM specific
Package to support this feature.
Diameter: This capability is not part of the current IPFilterRule
type definition. Rather than modify the IPFilterRule type, MIDCOM
could group it with other AVPs which add the missing information.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.2.10 Consecutive range of port numbers
SNMP: P+, RSIP: T, Megaco: P+, Diameter: P+, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
MIDCOM MIB module. SMI, the language used for defining MIB modules,
is flexible enough to allow the implementation of a MIB module to
meet the semantics of this requirement.
RSIP: The ports parameter of the RSIP ASSIGN_REQUESTs specifically
allows multiple, consecutive port numbers to be specified.
Megaco: Megaco can be easily extended using a MIDCOM specific
Package to support this feature.
Diameter: This capability is not part of the current IPFilterRule
type definition. Rather than modify the IPFilterRule type, MIDCOM
could group it with other AVPs which add the missing information.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.2.11 More precise rulesets contradicting overlapping rulesets
SNMP: P+, RSIP: P+, Megaco: P+, Diameter: T, COPS: P+
SNMP: This requirement can be met by an appropriate definition of a
MIDCOM MIB module.
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RSIP: To support this requirement, a new optional boolean
parameter, overlapOK, can be added to the RSIP ASSIGN_REQUESTs. If
the parameter is TRUE, the binding may overlap with an existing
binding. If the parameter is unspecified, or is FALSE, the binding
will not overlap with an existing binding, thus maintaining
backward compatibility with the current definition of RSIP.
Megaco: This requirement would be met if the policy in the
Middlebox allows contradictory, overlapping policy rules to be
installed.
Diameter: Allowed by the IPFilterRule semantics described in
Appendix D.
COPS: The COPS protocol has all the flexibility to meet this
requirement by using a COPS MIDCOM specific client or a MIDCOM
specific PIB.
2.3 General Security Requirements
This section contains the individual protocols as evaluated against
the General Security requirements from section 2.3 of the
requirements document [1]. A short description of each of the
protocols is provided to substantiate the evaluation.
2.3.1 Message Authentication, confidentiality and Integrity
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: SNMPv3 includes the User-based Security Model (USM,
[RFC2574]), which defines three standardized methods for providing
authentication, confidentiality, and integrity. Additionally, USM
has specific built-in mechanisms for preventing replay attacks
including unique protocol engine IDs, timers and counters per
engine and time windows for the validity of messages.
RSIP: This requirement can be met by operating RSIP over IPSec. The
RSIP framework recommends all communication between an RSIP host
and gateway be authenticated. Authentication, in the form of a
message hash appended to the end of each RSIP protocol packet, can
serve to authenticate the RSIP host and gateway to one another,
provide message integrity, and avoid replay attacks with an anti-
replay counter. However, the message hash and replay counter
parameters would need to be defined for the RSIP protocol.
Megaco: Megaco provides for these functions with the combined usage
of IPSEC or TLS.
Diameter: Diameter relies on either IPSEC or TLS for these
functions.
COPS: COPS has built-in message level security for authentication,
replay protection, and message integrity. COPS can also use TLS or
IPSec, thus reusing existing security mechanisms that have
interoperated in the markets.
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2.3.2 Optional Confidentiality Protection
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: SNMPv3 includes the User-based Security Model, which defines
three standardized methods for providing authentication,
confidentiality, and integrity, and is open to add further methods.
The method to use can be optionally chosen.
RSIP: Refer to 2.3.1.
Megaco: Refer to 2.3.1
Diameter: Implementation support of IPSEC ESP in Diameter
applications is not optional. Deployment of either IPSEC or TLS is
optional.
COPS: Refer to 2.3.1.
2.3.3 Operate Across Untrusted Domains
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: The User-based Security Model of SNMPv3 defines three
standardized methods for providing authentication, confidentiality,
and integrity, and it is open to add further methods. These methods
operate securely across untrusted domains.
RSIP: Refer to 2.3.1.
Megaco: Refer to 2.3.1.
Diameter: The Diameter specification [28] recommends the use of TLS
across untrusted domains.
COPS: Refer to 2.3.1
2.3.4 Mitigates Replay Attacks on Control Messages
SNMP: T, RSIP: T, Megaco: T, Diameter: T, COPS: T
SNMP: The User-based Security Model for SNMPv3 has specific built-
in mechanisms for preventing replay attacks including unique
protocol engine IDs, timers and counters per engine and time
windows for the validity of messages.
RSIP: Refer to 2.3.1
Megaco: Megaco commands and responses include matching transaction
identifiers. The recipient receiving the same transaction id
multiple times would discard the message, thus providing some
protection against replay attacks. If even stronger protection
against replay attack is needed, Megaco provides for the use of
IPSec or TLS.
Diameter: Diameter requires that implementations support the replay
protection mechanisms of IPSEC.
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COPS: Refer to 2.3.1
3 Conclusions
The overall statistics with regards to the number of Fully
Compliant, Partially Compliant (P+ and P) and Failing Compliancy
requirements for each of the protocols is summarized in table 1.
T P+ P F
-----------------------------------------------------------------
SNMP 22 5 0 0
RSIP 17 7 3 0
Megaco 19 5 3 0
Diameter 21 5 1 0
COPS 20 5 2 0
Table 1: Totals across all Requirements
In considering the P+ category of compliancy, an important aspect
is the mechanism for support of extensibility. The extension
mechanism provided by SNMP and COPS-PR using MIBs and PIBs
respectively, provides extensions with no impact to the protocol.
Diameter extensions require protocol changes, thus has a higher
impact, although the extensions can be handled by other Diameter
entities without being understood. Megaco's extension mechanisms
of packages also requires protocol changes that must be understand
by both sending and receiving entities, also being considered
higher impact. The RSIP extension mechanism has the largest impact
on the existing protocol and is based upon defining the necessary
new parameters.
The SNMP management framework meets all the specified MIDCOM
protocol requirements with the appropriate design of a MIDCOM MIB
module. SNMP is a proven technology with stable and proven
development tools, already has extensions defined to support NAT
configuration and policy-based management. SNMPv3 is a full
standard, is more mature and has undergone more validation than the
other protocols in the evaluation, and has been deployed to manage
large-scale real-world networks (e.g. DOCSIS cable modem networks).
The applicability of SNMP to the MIDCOM framework has a restriction
in that it assumes the MIDCOM PDP is part of the Middlebox.
RSIP fully meets many of the MIDCOM requirements. However, it does
require additions and extensions to meet several of the
requirements. RSIP would also require several framework elements to
be added to the MIDCOM framework as identified in section 1.2.3. In
addition, the tunneling required for RSIP as described in section
1.2.4, results in RSIP not being acceptable by the WG as the MIDCOM
protocol.
Megaco fully meets most of the key requirements for the MIDCOM
Protocol. Additional extensions in the form of a new Termination /
Package definition would be required for MIDCOM to meet several of
the requirements. In order to meet the remaining requirements,
modeling the underlying Middlebox resources (e.g., filters, policy
rules) as separate elements from the Megaco entities might allow
the usage of the protocol as-is, satisfying some of the resource
access control requirements.
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The Diameter evaluation indicated a good overall fit. Some
partially met requirements were identified that could be addressed
by a new application extension. However, the Diameter architecture
may be too heavy for the MIDCOM application and clearly much of the
Diameter base is not needed. In addition, Diameter is the only
protocol in the evaluation for which the RFCs are not yet
published. Other than these reservations, the protocol is a good
fit to MIDCOM requirements.
The COPS evaluation indicates that the protocol meets the majority
of the MIDCOM protocol requirements by using the protocol's native
extension techniques, with COPS-PR being explicitly required to
meet requirements 2.1.3 and 2.2.3. In order to fully satisfy one
partially met requirement, 2.1.1, the COPS model would need to
allow a PDP to establish communication with a PEP. While not
explicitly prohibited by the COPS model, this would require
additions, in the form of local policy, to ensure the proper
establishment of an authorized association.
Security Considerations
Security considerations for the MIDCOM protocol are covered by the
comparison against the specific Security requirements in the MIDCOM
requirements document [1] and are specifically addressed by section
2.1.8 and section 2.3.
Normative References
[1] R. Swale, P. Mart, P. Sijben, S. Brim, M. Shore, "Middlebox
Communications (MIDCOM) Protocol Requirements", RFC 3304, August,
2002.
[2] P. Srisuresh, J. Kuthan, J. Rosenberg, A. Molitor, A. Rayhan,
"Middlebox Communications Architecture and Framework", RFC 3303,
August, 2002.
[3] Rose, M., and K. McCloghrie, "Management Information Base for
Network Management of TCP/IP-based internets: MIB-II", RFC 1213,
March, 1991.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[5] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture
for Describing SNMP Management Frameworks", STD 62, RFC 3411,
November 2002.
[6] Rose, M., and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16, RFC
1155, May 1990.
[7] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.
[8] M. Rose, "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.
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[9] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M., and S. Waldbusser, "Structure of Management Information Version
2 (SMIv2)", STD 58, RFC 2578, April 1999.
[10] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Textual Conventions for SMIv2", STD
58, RFC 2579, April 1999.
[11] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J.,
Rose, M., and S. Waldbusser, "Conformance Statements for SMIv2",
STD 58, RFC 2580, April 1999.
[12] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, May 1990.
[13] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901, January 1996.
[14] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Transport Mappings for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1906, January 1996.
[15] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", STD 62, RFC 3412, November 2002.
[16] Blumenthal, U., and B. Wijnen, "User-based Security Model(USM)
for version 3 of the Simple Network Management Protocol (SNMPv3)",
STD 62, RFC 3414, November 2002.
[17] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network Management
Protocol (SNMPv2)", RFC 1905, January 1996.
[18] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications",
STD 62, RFC 3413, November 2002.
[19] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access
Control Model (VACM) for the Simple Network Management Protocol
(SNMP)", STD 62, RFC 3415, November 2002.
[20] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction to Version 3 of the Internet-standard Network
Management Framework", 3410, November 2002.
[21] M. Borella, J. Lo, D. Grabelsky, G. Montenegro, "Realm
Specific IP: Framework", RFC 3102, October, 2001.
[22] M. Borella, D. Grabelsky, J. Lo, K. Taniguchi, "Realm Specific
IP: Protocol Specification",_RFC 3103, October 2001.
[23] G. Montenegro, M. Borella, "RSIP Support for End-to-end
Ipsec", RFC 3104, October 2001.
[24] J. Kempf, G. Montenegro, "Finding an RSIP Server with SLP",
RFC 3105, October 2001.
[25] F. Cuervo, N. Greene, A. Rayhan, C. Huitema, B. Rosen, J.
Segers, "Megaco Protocol Version 1.0", RFC 3015, November, 2000.
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[26] S. Kent, R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[27] S. Kent, R. Atkinson, "IP Encapsulating Security Payload",
RFC 2406, November 1998.
[28] P. Calhoun, J. Arkko, E. Guttman, G. Zorn, J. Loughney,
"Diameter Base Protocol", draft-ietf-aaa-diameter-15.txt, IETF
work in progress, October 2002.
[29] P. Calhoun, G. Zorn, P. Pan, H. Akhtar, "Diameter Framework
Document", draft-ietf-aaa-diameter-framework-01.txt, IETF work in
progress, March 2001.
[30] P. Calhoun, W. Bulley, A. Rubens, J. Haag, G. Zorn, D.
Spence, "Diameter NASREQ Application", draft-ietf-aaa-diameter-
nasreq-09.txt, IETF work in progress, March 2002.
[31] D.Durham et al, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000.
[32] K. Chan, D. Durham, S. Gai, S. Herzog, K. McCloghrie, F.
Reichmeyer, J. Seligson, A. Smith, R. Yavatkar, "COPS Usage
for Policy Provisioning", RFC 3084, March 2001.
[33] D. Raz, J. Schoenwalder, B. Sugla, "An SNMP Application Level
Gateway for Payload Address Translation", RFC 2962, October 2000.
Informative References
[34] K. McCloghrie, F. Kastenholz, " The Interfaces Group MIB", RFC
2863, June, 2000.
Contributors
The following identifies the key contributors who provided the primary
content for this document in the form of individual drafts for each
protocol:
RSIP
Jim Renkel
The CommWorks Corp., a 3Com company
3800 Golf Rd. Phone: +1.847.262.2539
Rolling Meadows, IL, USA Email:james_renkel@commworks.com
SNMP
Juergen Quittek
NEC Europe Ltd.
Network Laboratories
Kurfuersten-Anlage 34
69115 Heidelberg Phone: +49 6221 90511-15
Germany Email: quittek@ccrle.nec.de
David Harrington Co-chair SNMPv3 WG
Enterasys Networks
35 Industrial Way Phone: +1 603-337-2614
Rochester, NH 03867-5005 EMail: dbh@enterasys.com
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Megaco
Sanjoy Sen
Cedric Aoun
Nortel Networks Email: cedric.aoun@nortelnetworks.com
Tom Taylor
Nortel Networks Email: taylor@nortelnetworks.com
Diameter
Tom Taylor
Nortel Networks
1852 Lorraine Ave.
Ottawa, Ontario Phone: +1 613 736 0961
Canada K1H 6Z8 Email: taylor@nortelnetworks.com
COPS
Cedric Aoun
Nortel Networks
FRANCE Email: cedric.aoun@nortelnetworks.com
Kwok-Ho Chan
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821 Email: khchan@nortelnetworks.com
Louis-Nicolas Hamer
Nortel Networks
PO Box 3511 Station C
Ottawa, Ontario Phone: +1 613.768.3409
Canada K1Y 4H7 Email: nhamer@nortelnetworks.com
Reinaldo Penno
Nortel Networks
2305 Mission College Boulevard
Building SC9
Santa Clara, CA 95054 Email: rpenno@nortelnetworks.com
Sanjoy Sen
Acknowledgements
The editor would like to acknowledge the constructive feedback
provided by Joel M. Halpern on the individual protocol evaluation
contributions. In addition, a thanks to Elwyn Davies, Christopher
Martin, Bob Penfield, Scott Brim and Martin Stiemerling for
contributing to the mailing list discussion on the draft content.
Author's Address
Mary Barnes
Nortel Networks
2380 Performance Drive Phone: 1-972-684-5432
Richardson, TX USA Email: mbarnes@nortelnetworks.com
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Appendix A - SNMP Overview
The SNMP Management Framework presently consists of five major
components:
o An overall architecture, described in RFC 3411 [RFC3411]. A
more detailed introduction and applicability statements for
the SNMP Management Framework can be found in RFC 3410
[RFC3410].
o Mechanisms for describing and naming objects and events for
the purpose of management. The current version of this
Structure of Management Information (SMI) is called called
SMIv2 and described in RFC 2578 [RFC2578], RFC 2579 [RFC2579]
and RFC 2580 [RFC2580].
o Message protocols for transferring management information.
The current version of the message protocol is called SNMPv3
and described in RFC 3412 [RFC3412], RFC 3414 [RFC3414] and
RFC 3417 [RFC3417].
o Protocol operations for accessing management information. The
current version of the protocol operations and associated PDU
formats is described in RFC 3416 [RFC3416].
o A set of fundamental applications described in RFC 3413
[RFC3413] and the view-based access control mechanism
described in RFC 3415 [RFC2415].
Managed objects are accessed via a virtual information store,
termed the Management Information Base or MIB. Objects in the MIB
are defined using the mechanisms defined in the SMI.
A.1 SNMPv3 Proxy Forwarding
SNMPv3 proxy forwarding (RFC3413) provides a standardized mechanism
to configure an intermediate node to forward SNMP messages. A
command generating entity sends requests to a proxy forwarding
entity that forwards the request to a third entity.
One SNMP entity may serve both functions û as the SNMP ôagentö to
monitor and configure the node on which it is resident, and as an
intermediate node in a proxy relationship to permit monitoring and
configuration of additional entities.
Each entity is identified by a unique engineID value, specifically
to support proxy between addressing domains and/or trust domains.
An SNMPv3 message contains two engineIDs- one to identify the
database to be used for message security, and one to identify the
source (or target) of the contained data. Message security is
applied between the originator and the proxy, and then between the
proxy and the end-target. The PDU contains the engineID of the node
whose data is contained in the message, which passes end-to-end,
unchanged by the proxy.
SNMPv3 proxy was designed to provide a standard SNMP approach to
inserting an intermediate node in the middle of communications for
a variety of scenarios. SNMPv3 proxy can support crossing
addressing domains, such as IPv4 and IPv6, crossing SNMP version
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domains, such as SNMPv3 and SNMPv1, crossing security mechanism
domains, such as DES and AES, and for providing a single point of
management contact for a subset of the network, such as managing a
private network through a NAT device or a VPN endpoint.
A.2 Proxies versus Application Level Gateways
Proxies are generally preferred to Application Level Gateways for
SNMP. ALGs typically modify the headers and content of messages.
SNMP is a protocol designed for troubleshooting network (mis-)
configurations. Because an operator needs to understand the actual
configuration, the translation of addresses within SNMP data causes
confusion, hiding the actual configuration of a managed device from
the operator. ALGs also introduce security vulnerabilities, and
other complexities related to modifying SNMP data.
SNMP Proxies can modify message headers without modifying the
contained data. This avoids the issues associated with translating
the payload data, while permitting application level translation of
addresses.
The issues of ALGs versus proxies for SNMP Payload Address
Translation are discussed at length in RFC2962.
Appendix B - RSIP with tunneling
NAT requires ALGs (Application Layer Gateways) in middleboxes
without MIDCOM, and application modifications or agents for
middleboxes with MIDCOM.
Support for NAT without tunneling could easily be added to the RSIP
control protocol. NAT would be defined as a new, null tunnel type.
Support for the NAT null tunnels could be implemented in hosts, or
in applications or application agents.
If support for NAT null tunnels were implemented in hosts, no
modifications to applications would be required, and no application
agents or ALGs would be required. This has obvious advantages. In
addition to the NAT null tunnel, the host would have to implement
an RSIP / MIDCOM client (or a STUN client) and the middlebox would
have to implement an RSIP / MIDCOM server, or a STUN server would
have to be available _beyond_ the middlebox. Note that the STUN
client / server approach may not work with all types of
middleboxes.
If support for NAT null tunnels were NOT implemented in hosts, then
applications would have to be modified, or application agents or
ALGs would have to be implemented. This has the advantage over
tunnels (whether null or not) of not requiring modification to
hosts, but would require the modification of host applications or
the implementation of application agents, both of which would
include an RSIP / MIDCOM client, and the implementation of an
RSIP/MIDCOM server in the middlebox. Again, in some situations,
STUN could be used instead of RSIP / MIDCOM.
Tunneled or not, an RSIP / MIDCOM server is needed in the
middlebox. Tunneled, the host needs to be modified, but not the
application. Untunneled, an agent must be added or the application
must be modified, but there would be no host modifications. The
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advantages/disadvantages of tunneling would need to be evaluated in
considering RSIP.
Appendix C - Megaco Modeling Approach
To model the Middlebox functions such as firewall, NAT etc., a new
Middlebox Termination type needs to be defined within Megaco. If
policy-rule overlap or modification by multiple Agents is NOT
required, then a policy rule is equivalent to a Termination (see
Figure 1). The various components of a Policy rule such as filter,
action, life-time, creator etc. are described as various properties
of a Termination. Use of the Virtual Media Gateway (VMG) concept
allows for conflict-free interaction of multiple MA's with the same
MB.
+-------+ +-------+
| MA-1 | | MA-2 |
| | | |
+-------+ |IF2 +-------+
| | |
+-------------|---------|----------|-----------+
| +---------+ | +-------------+ |
IF1 |VMG1 | +--+ | | | +--+ +--+ |VMG2 |IF3
----------| |Tx|-------+ +---|Ty|--|Tz|----------------
| | +--+ | | | +--+ +--+ | |
| ....| | | +-------------+ |
| +---------+ | |
| +---------------------------------
| Middlebox | IF4
+----------------------------------------------+
Tx: Termination x = Policy rule x
Ty: Termination y = Policy rule y
Tz: Termination z = Policy rule z
MA: MIDCOM Agent
IF: Interface
Figure 1.
If it is required to allow multiple agents manipulate the same
Middlebox resource (e.g., a Policy rule or a filter), the latter
needs to be kept separate from the Termination (the Policy rule is
manipulated by the MA by manipulating the properties of the
associated Termination). For example, if overlapping policy rule
manipulation is required, then a Termination shall be associated
with a single policy rule, but a policy rule may be associated with
more than one Termination. Thus, a Termination can share a policy
rule with another Termination, or have a policy rule partially
overlapping with that of another Termination. This model allows two
MAËs, controlling two distinct Terminations (see Figure 2),
manipulate the same or overlapping policy rules. In Figure 2,
policy rules 1 and 2 are overlapping and they are shared by MA-1
and MA-2.
+-------+ +-------+
| MA-1 | | MA-2 |
| | | |
+-------+ |IF2 +-------+
| | | MB
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+-------------|---------|----------|-----------+
| +-----------+ | +-------------+ |
IF1 |VMG1 | +--+ | | | +--+ +--+ |VMG2 |IF3
------------------|Ty|----+ +---|Tx|--|Tz|----------------
| | +--+ | | | +--+ +--+ | |
| .... | | | | +--/------\---+ |
| +-------|---+ | / \ |
| | +----/----------\------------------
| +------+----+------+ +------+ |IF4
| |Policy1 Policy2 | |Policy| |
| | | | | | 3 | |
| +----+------+------+ +------+ |
+----------------------------------------------+
Tx: Termination x
Ty: Termination y
Tz: Termination z
MA: MIDCOM Agent
IF: Interface
MB: Middlebox
Figure 2.
This requires that the Agent and the Middlebox adhere to the
following principles:
(1) Only one Termination has read/write access to a filter at any
time.
(2) When the policy rule is being modified by a new agent (i.e.
not the one that created the policy) the Middlebox makes a policy
decision and decides whether to accept the requested modification
or not. In the case the modification is accepted the initial MIDCOM
agent may be notified.
Appendix D - Diameter IPFilter Rule
The IPFilterRule format is derived from the OctetString AVP Base
Format. It uses the UTF-8 encoding and has the same requirements
as the UTF8String. Packets may be filtered based on the following
information that is associated with it:
Direction (in or out)
Source and destination IP address (possibly masked)
Protocol
Source and destination port (lists or ranges)
TCP flags
IP fragment flag
IP options
ICMP types
Rules for the appropriate direction are evaluated in order, with
the first matched rule terminating the evaluation. Each packet is
evaluated once. If no rule matches, the packet is dropped if the
last rule evaluated was a permit, and passed if the last rule was a
deny.
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IPFilterRule filters MUST follow the format:
action dir proto from src to dst [options]
action permit - Allow packets that match the rule.
deny - Drop packets that match the rule.
dir "in" is from the terminal, "out" is to the
terminal.
proto An IP protocol specified by number. The "ip"
keyword means any protocol will match.
src and dst <address/mask> [ports]
The <address/mask> may be specified as:
ipno An IPv4 or IPv6 number in dotted-
quad or canonical IPv6 form. Only
this exact IP number will match the
rule.
ipno/bits An IP number as above with a mask
width of the form 1.2.3.4/24. In
this case, all IP numbers from
1.2.3.0 to 1.2.3.255 will match.
The bit width MUST be valid for the
IP version and the IP number MUST
NOT have bits set beyond the mask.
For a match to occur, the same IP
version must be present in the
packet that was used in describing
the IP address. To test for a
particular IP version, the bits part
can be set to zero. The keyword
"any" is 0.0.0.0/0 or the IPv6
equivalent. The keyword "assigned"
is the address or set of addresses
assigned to the terminal. For IPv4,
a typical first rule is often
"deny in ip! assigned"
The sense of the match can be inverted by
preceding an address with the not modifier (!),
causing all other addresses to be matched
instead. This does not affect the selection of
port numbers.
With the TCP, UDP and SCTP protocols, optional
ports may be specified as:
{port|port-port}[,ports[,...]]
The '-' notation specifies a range of ports
(including boundaries).
Fragmented packets that have a non-zero offset
(i.e. not the first fragment) will never match
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a rule that has one or more port
specifications. See the frag option for
details on matching fragmented packets.
options:
frag Match if the packet is a fragment and this is not
the first fragment of the datagram. frag may not
be used in conjunction with either tcpflags or
TCP/UDP port specifications.
ipoptions spec
Match if the IP header contains the comma
separated list of options specified in spec. The
supported IP options are:
ssrr (strict source route), lsrr (loose source
route), rr (record packet route) and ts
(timestamp). The absence of a particular option
may be denoted with a '!'.
tcpoptions spec
Match if the TCP header contains the comma
separated list of options specified in spec. The
supported TCP options are:
mss (maximum segment size), window (tcp window
advertisement), sack (selective ack), ts (rfc1323
timestamp) and cc (rfc1644 t/tcp connection
count). The absence of a particular option may
be denoted with a '!'.
established
TCP packets only. Match packets that have the RST
or ACK bits set.
setup TCP packets only. Match packets that have the SYN
bit set but no ACK bit.
tcpflags spec
TCP packets only. Match if the TCP header
contains the comma separated list of flags
specified in spec. The supported TCP flags are:
fin, syn, rst, psh, ack and urg. The absence of a
particular flag may be denoted with a '!'. A rule
that contains a tcpflags specification can never
match a fragmented packet that has a non-zero
offset. See the frag option for details on
matching fragmented packets.
icmptypes types
ICMP packets only. Match if the ICMP type is in
the list types. The list may be specified as any
combination of ranges or individual types
separated by commas. Both the numeric values and
the symbolic values listed below can be used. The
supported ICMP types are:
echo reply (0), destination unreachable (3),
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source quench (4), redirect (5), echo request
(8), router advertisement (9), router
solicitation (10), time-to-live exceeded (11), IP
header bad (12), timestamp request (13),
timestamp reply (14), information request (15),
information reply (16), address mask request (17)
and address mask reply (18).
There is one kind of packet that the access device MUST always
discard, that is an IP fragment with a fragment offset of one. This
is a valid packet, but it only has one use, to try to circumvent
firewalls.
An access device that is unable to interpret or apply a deny rule
MUST terminate the session. An access device that is unable to
interpret or apply a permit rule MAY apply a more restrictive rule.
An access device MAY apply deny rules of its own before the
supplied rules, for example to protect the access device owner's
infrastructure.
The rule syntax is a modified subset of ipfw(8) from FreeBSD, and
the ipfw.c code may provide a useful base for implementations.
Intellectual Property Statements
The IETF has been notified of intellectual property rights claimed
in regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
Full Copyright Statement
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