Inter-Domain Routing H. Gredler
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track J. Medved
Expires: April 25, 2013 S. Previdi
Cisco Systems, Inc.
A. Farrel
Juniper Networks, Inc.
S. Ray
Cisco Systems, Inc.
October 22, 2012
North-Bound Distribution of Link-State and TE Information using BGP
draft-ietf-idr-ls-distribution-01
Abstract
In a number of environments, a component external to a network is
called upon to perform computations based on the network topology and
current state of the connections within the network, including
traffic engineering information. This is information typically
distributed by IGP routing protocols within the network
This document describes a mechanism by which links state and traffic
engineering information can be collected from networks and shared
with external components using the BGP routing protocol. This is
achieved using a new BGP Network Layer Reachability Information
(NLRI) encoding format. The mechanism is applicable to physical and
virtual links. The mechanism described is subject to policy control.
Applications of this technique include Application Layer Traffic
Optimization (ALTO) servers, and Path Computation Elements (PCEs).
Requirements Language
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 [RFC2119].
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/.
Gredler, et al. Expires April 25, 2013 [Page 1]
Internet-Draft Link-State Info Distribution using BGP October 2012
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 April 25, 2013.
Copyright Notice
Copyright (c) 2012 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
(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.
Gredler, et al. Expires April 25, 2013 [Page 2]
Internet-Draft Link-State Info Distribution using BGP October 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Motivation and Applicability . . . . . . . . . . . . . . . . . 5
2.1. MPLS-TE with PCE . . . . . . . . . . . . . . . . . . . . . 5
2.2. ALTO Server Network API . . . . . . . . . . . . . . . . . 7
3. Carrying Link State Information in BGP . . . . . . . . . . . . 8
3.1. TLV Format . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. The Link State NLRI . . . . . . . . . . . . . . . . . . . 9
3.2.1. Node Descriptors . . . . . . . . . . . . . . . . . . . 11
3.2.2. Link Descriptors . . . . . . . . . . . . . . . . . . . 15
3.2.3. The Prefix NLRI . . . . . . . . . . . . . . . . . . . 16
3.3. The LINK_STATE Attribute . . . . . . . . . . . . . . . . . 16
3.3.1. Link Attribute TLVs . . . . . . . . . . . . . . . . . 16
3.3.2. Node Attribute TLVs . . . . . . . . . . . . . . . . . 20
3.3.3. Prefix Attributes TLVs . . . . . . . . . . . . . . . . 23
3.4. BGP Next Hop Information . . . . . . . . . . . . . . . . . 27
3.5. Inter-AS Links . . . . . . . . . . . . . . . . . . . . . . 27
4. Link to Path Aggregation . . . . . . . . . . . . . . . . . . . 27
4.1. Example: No Link Aggregation . . . . . . . . . . . . . . . 27
4.2. Example: ASBR to ASBR Path Aggregation . . . . . . . . . . 28
4.3. Example: Multi-AS Path Aggregation . . . . . . . . . . . . 28
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
6. Manageability Considerations . . . . . . . . . . . . . . . . . 29
6.1. Operational Considerations . . . . . . . . . . . . . . . . 29
6.1.1. Operations . . . . . . . . . . . . . . . . . . . . . . 29
6.1.2. Installation and Initial Setup . . . . . . . . . . . . 30
6.1.3. Migration Path . . . . . . . . . . . . . . . . . . . . 30
6.1.4. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . 30
6.1.5. Impact on Network Operation . . . . . . . . . . . . . 30
6.1.6. Verifying Correct Operation . . . . . . . . . . . . . 30
6.2. Management Considerations . . . . . . . . . . . . . . . . 31
6.2.1. Management Information . . . . . . . . . . . . . . . . 31
6.2.2. Fault Management . . . . . . . . . . . . . . . . . . . 31
6.2.3. Configuration Management . . . . . . . . . . . . . . . 31
6.2.4. Accounting Management . . . . . . . . . . . . . . . . 31
6.2.5. Performance Management . . . . . . . . . . . . . . . . 31
6.2.6. Security Management . . . . . . . . . . . . . . . . . 32
7. Security Considerations . . . . . . . . . . . . . . . . . . . 32
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.1. Normative References . . . . . . . . . . . . . . . . . . . 32
9.2. Informative References . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34
Gredler, et al. Expires April 25, 2013 [Page 3]
Internet-Draft Link-State Info Distribution using BGP October 2012
1. Introduction
The contents of a Link State Database (LSDB) or a Traffic Engineering
Database (TED) has the scope of an IGP area. Some applications, such
as end-to-end Traffic Engineering (TE), would benefit from visibility
outside one area or Autonomous System (AS) in order to make better
decisions.
The IETF has defined the Path Computation Element (PCE) [RFC4655] as
a mechanism for achieving the computation of end-to-end TE paths that
cross the visibility of more than one TED or which require CPU-
intensive or coordinated computations. The IETF has also defined the
ALTO Server [RFC5693] as an entity that generates an abstracted
network topology and provides it to network-aware applications.
Both a PCE and an ALTO Server need to gather information about the
topologies and capabilities of the network in order to be able to
fulfill their function
This document describes a mechanism by which Link State and TE
information can be collected from networks and shared with external
components using the BGP routing protocol [RFC4271]. This is
achieved using a new BGP Network Layer Reachability Information
(NLRI) encoding format. The mechanism is applicable to physical and
virtual links. The mechanism described is subject to policy control.
A router maintains one or more databases for storing link-state
information about nodes and links in any given area. Link attributes
stored in these databases include: local/remote IP addresses, local/
remote interface identifiers, link metric and TE metric, link
bandwidth, reservable bandwidth, per CoS class reservation state,
preemption and Shared Risk Link Groups (SRLG). The router's BGP
process can retrieve topology from these LSDBs and distribute it to a
consumer, either directly or via a peer BGP Speaker (typically a
dedicated Route Reflector), using the encoding specified in this
document.
The collection of Link State and TE link state information and its
distribution to consumers is shown in the following figure.
Gredler, et al. Expires April 25, 2013 [Page 4]
Internet-Draft Link-State Info Distribution using BGP October 2012
+-----------+
| Consumer |
+-----------+
^
|
+-----------+
| BGP | +-----------+
| Speaker | | Consumer |
+-----------+ +-----------+
^ ^ ^ ^
| | | |
+---------------+ | +-------------------+ |
| | | |
+-----------+ +-----------+ +-----------+
| BGP | | BGP | | BGP |
| Speaker | | Speaker | . . . | Speaker |
+-----------+ +-----------+ +-----------+
^ ^ ^
| | |
IGP IGP IGP
Figure 1: TE Link State info collection
A BGP Speaker may apply configurable policy to the information that
it distributes. Thus, it may distribute the real physical topology
from the LSDB or the TED. Alternatively, it may create an abstracted
topology, where virtual, aggregated nodes are connected by virtual
paths. Aggregated nodes can be created, for example, out of multiple
routers in a POP. Abstracted topology can also be a mix of physical
and virtual nodes and physical and virtual links. Furthermore, the
BGP Speaker can apply policy to determine when information is updated
to the consumer so that there is reduction of information flow form
the network to the consumers. Mechanisms through which topologies
can be aggregated or virtualized are outside the scope of this
document
2. Motivation and Applicability
This section describes uses cases from which the requirements can be
derived.
2.1. MPLS-TE with PCE
As described in [RFC4655] a PCE can be used to compute MPLS-TE paths
within a "domain" (such as an IGP area) or across multiple domains
(such as a multi-area AS, or multiple ASes).
Gredler, et al. Expires April 25, 2013 [Page 5]
Internet-Draft Link-State Info Distribution using BGP October 2012
o Within a single area, the PCE offers enhanced computational power
that may not be available on individual routers, sophisticated
policy control and algorithms, and coordination of computation
across the whole area.
o If a router wants to compute a MPLS-TE path across IGP areas its
own TED lacks visibility of the complete topology. That means
that the router cannot determine the end-to-end path, and cannot
even select the right exit router (Area Border Router - ABR) for
an optimal path. This is an issue for large-scale networks that
need to segment their core networks into distinct areas, but which
still want to take advantage of MPLS-TE.
Previous solutions used per-domain path computation [RFC5152]. The
source router could only compute the path for the first area because
the router only has full topological visibility for the first area
along the path, but not for subsequent areas. Per-domain path
computation uses a technique called "loose-hop-expansion" [RFC3209],
and selects the exit ABR and other ABRs or AS Border Routers (ASBRs)
using the IGP computed shortest path topology for the remainder of
the path. This may lead to sub-optimal paths, makes alternate/
back-up path computation hard, and might result in no TE path being
found when one really does exist.
The PCE presents a computation server that may have visibility into
more than one IGP area or AS, or may cooperate with other PCEs to
perform distributed path computation. The PCE obviously needs access
to the TED for the area(s) it serves, but [RFC4655] does not describe
how this is achieved. Many implementations make the PCE a passive
participant in the IGP so that it can learn the latest state of the
network, but this may be sub-optimal when the network is subject to a
high degree of churn, or when the PCE is responsible for multiple
areas.
The following figure shows how a PCE can get its TED information
using the mechanism described in this document.
Gredler, et al. Expires April 25, 2013 [Page 6]
Internet-Draft Link-State Info Distribution using BGP October 2012
+----------+ +---------+
| ----- | | BGP |
| | TED |<-+-------------------------->| Speaker |
| ----- | TED synchronization | |
| | | mechanism: +---------+
| | | BGP with Link-State NLRI
| v |
| ----- |
| | PCE | |
| ----- |
+----------+
^
| Request/
| Response
v
Service +----------+ Signaling +----------+
Request | Head-End | Protocol | Adjacent |
-------->| Node |<------------>| Node |
+----------+ +----------+
Figure 2: External PCE node using a TED synchronization mechanism
The mechanism in this document allows the necessary TED information
to be collected from the IGP within the network, filtered according
to configurable policy, and distributed to the PCE as necessary.
2.2. ALTO Server Network API
An ALTO Server [RFC5693] is an entity that generates an abstracted
network topology and provides it to network-aware applications over a
web service based API. Example applications are p2p clients or
trackers, or CDNs. The abstracted network topology comes in the form
of two maps: a Network Map that specifies allocation of prefixes to
PIDs, and a Cost Map that specifies the cost between PIDs listed in
the Network Map. For more details, see [I-D.ietf-alto-protocol].
ALTO abstract network topologies can be auto-generated from the
physical topology of the underlying network. The generation would
typically be based on policies and rules set by the operator. Both
prefix and TE data are required: prefix data is required to generate
ALTO Network Maps, TE (topology) data is required to generate ALTO
Cost Maps. Prefix data is carried and originated in BGP, TE data is
originated and carried in an IGP. The mechanism defined in this
document provides a single interface through which an ALTO Server can
retrieve all the necessary prefix and network topology data from the
underlying network. Note an ALTO Server can use other mechanisms to
get network data, for example, peering with multiple IGP and BGP
Speakers.
Gredler, et al. Expires April 25, 2013 [Page 7]
Internet-Draft Link-State Info Distribution using BGP October 2012
The following figure shows how an ALTO Server can get network
topology information from the underlying network using the mechanism
described in this document.
+--------+
| Client |<--+
+--------+ |
| ALTO +--------+ BGP with +---------+
+--------+ | Protocol | ALTO | Link-State NLRI | BGP |
| Client |<--+------------| Server |<----------------| Speaker |
+--------+ | | | | |
| +--------+ +---------+
+--------+ |
| Client |<--+
+--------+
Figure 3: ALTO Server using network topology information
3. Carrying Link State Information in BGP
Two parts: a new BGP NLRI that describes links and nodes comprising
IGP link state information, and a new BGP path attribute that carries
link and node properties and attributes, such as the link metric or
node properties.
3.1. TLV Format
Information in the new link state NLRIs and attributes is encoded in
Type/Length/Value triplets. The TLV format is shown in Figure 4.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: TLV format
The Length field defines the length of the value portion in octets
(thus a TLV with no value portion would have a length of zero). The
TLV is not padded to four-octet alignment; Unrecognized types are
ignored.
Gredler, et al. Expires April 25, 2013 [Page 8]
Internet-Draft Link-State Info Distribution using BGP October 2012
3.2. The Link State NLRI
The MP_REACH and MP_UNREACH attributes are BGP's containers for
carrying opaque information. Each Link State NLRI describes either a
single node or link.
All link, node and prefix information SHALL be encoded using a TBD
AFI / TBD SAFI header into those attributes.
In order for two BGP speakers to exchange Link-State NLRI, they MUST
use BGP Capabilities Advertisement to ensure that they both are
capable of properly processing such NLRI. This is done as specified
in [RFC4760], by using capability code 1 (multi-protocol BGP), with
an AFI/SAFI TBD.
The format of the Link State NLRI is shown in the following figure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Link-State NLRI (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Link State SAFI 1 NLRI Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NLRI Type | Total NLRI Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Route Distinguisher +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Link-State NLRI (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Link State SAFI 128 NLRI Format
The 'Total NLRI Length' field contains the cumulative length of all
the TLVs in the NLRI. For VPN applications it also includes the
Gredler, et al. Expires April 25, 2013 [Page 9]
Internet-Draft Link-State Info Distribution using BGP October 2012
length of the Route Distinguisher.
The 'NLRI Type' field can contain one of the following values:
Type = 1: Link NLRI, contains link descriptors and link attributes
Type = 2: Node NLRI, contains node attributes
Type = 3: IPv4 Topology Prefix NLRI
Type = 4: IPv6 Topology Prefix NLRI
The Link NLRI (NLRI Type = 1) is shown in the following figure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-ID | Reserved | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Node Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Node Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Link NLRI format
The Node NLRI (NLRI Type = 2) is shown in the following figure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-ID | Reserved | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Node Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: The Node NLRI format
The IPv4 and IPv6 Prefix NLRIs (NLRI Type = 3 and Type = 4) use the
same format as shown in the following figure.
Gredler, et al. Expires April 25, 2013 [Page 10]
Internet-Draft Link-State Info Distribution using BGP October 2012
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-ID | Reserved | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix NLRI (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: The IPv4/IPv6 Topology Prefix NLRI format
The 'Protocol-ID' field can contain one of the following values:
Protocol-ID = 0: Unknown, The source of NLRI information could not
be determined
Protocol-ID: IS-IS Level 1, The NLRI information has been sourced
by IS-IS Level 1
Protocol-ID: IS-IS Level 2, The NLRI information has been sourced
by IS-IS Level 2
Protocol-ID = 3: OSPF, The NLRI information has been sourced by
OSPF
Protocol-ID = 4: Direct, The NLRI information has been sourced
from local interface state
Protocol-ID = 5: Static, The NLRI information has been sourced by
static configuration
Both OSPF and IS-IS may run multiple routing protocol instances over
the same link. See [I-D.ietf-isis-mi] and [RFC6549]. The 'Instance
Identifier' field identifies the protocol instance.
Each Node Descriptor and Link Descriptor consists of one or more TLVs
described in the following sections. The sender of an UPDATE message
MUST order the TLVs within a Node Descriptor or a Link Descriptor in
ascending order of TLV type."
3.2.1. Node Descriptors
Each link gets anchored by at least a pair of router-IDs. Since
there are many Router-IDs formats (32 Bit IPv4 router-ID, 56 Bit ISO
Node-ID and 128 Bit IPv6 router-ID) a link may be anchored by more
than one Router-ID pair. The set of Local and Remote Node
Descriptors describe which Protocols Router-IDs will be following to
Gredler, et al. Expires April 25, 2013 [Page 11]
Internet-Draft Link-State Info Distribution using BGP October 2012
"anchor" the link described by the "Link attribute TLVs". There must
be at least one "like" router-ID pair of a Local Node Descriptors and
a Remote Node Descriptors per-protocol. If a peer sends an illegal
combination in this respect, then this is handled as an NLRI error,
described in [RFC4760].
It is desirable that the Router-ID assignments inside the Node anchor
are globally unique. However there may be router-ID spaces (e.g.
ISO) where not even a global registry exists, or worse, Router-IDs
have been allocated following private-IP RFC 1918 [RFC1918]
allocation. In order to disambiguate the Router-IDs the local and
remote Autonomous System number TLVs of the anchor nodes MUST be
included in the NLRI. If the anchor node's AS is a member of an AS
Confederation ([RFC5065]), then the Autonomous System number TLV
contains the confederations' AS Confederation Identifier and the
Member-AS TLV is included in the NLRI. The Local and Remote
Autonomous System TLVs are 4 octets wide as described in [RFC4893].
2-octet AS Numbers SHALL be expanded to 4-octet AS Numbers by zeroing
the two MSB octets.
3.2.1.1. Local Node Descriptors
The Local Node Descriptors TLV (Type 256) contains Node Descriptors
for the node anchoring the local end of the link. The length of this
TLV is variable. The value contains one or more Node Descriptor Sub-
TLVs defined in Section 3.2.1.3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Node Descriptor Sub-TLVs (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Local Node Descriptors TLV format
3.2.1.2. Remote Node Descriptors
The Remote Node Descriptors TLV (Type 257) contains Node Descriptors
for the node anchoring the remote end of the link. The length of
this TLV is variable. The value contains one or more Node Descriptor
Sub-TLVs defined in Section 3.2.1.3.
Gredler, et al. Expires April 25, 2013 [Page 12]
Internet-Draft Link-State Info Distribution using BGP October 2012
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Node Descriptor Sub-TLVs (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Remote Node Descriptors TLV format
3.2.1.3. Node Descriptor Sub-TLVs
The Node Descriptor Sub-TLV type codepoints and lengths are listed in
the following table:
+------+-------------------+--------+
| Type | Description | Length |
+------+-------------------+--------+
| 258 | Autonomous System | 4 |
| 259 | Member-AS | 4 |
| 260 | ISO Node-ID | 7 |
| 261 | IPv4 Router-ID | 5 |
| 262 | IPv4 Router-ID | 17 |
+------+-------------------+--------+
Table 1: Node Descriptor Sub-TLVs
The TLV values in Node Descriptor Sub-TLVs are defined as follows:
Autonomous System: opaque value (32 Bit AS ID)
Member-AS: opaque value (32 Bit AS ID); only included if the node is
in an AS confederation.
IPv4 Router ID: opaque value (can be an IPv4 address or an 32 Bit
router ID).
IPv6 Router ID: opaque value (can be an IPv6 address or 128 Bit
router ID).
ISO Node ID: ISO node-ID (6 octets ISO system-ID) followed by a PSN
octet in case LAN "Pseudonode" information gets advertised. The
PSN octet must be zero for non-LAN "Pseudonodes".
Gredler, et al. Expires April 25, 2013 [Page 13]
Internet-Draft Link-State Info Distribution using BGP October 2012
There can be at most one instance of each TLV type present in any
Node Descriptor. The TLV ordering within a Node descriptor MUST
be kept in order of increasing numeric value of type. TLVs 258
and 259 specify administrative context in which TLVs 260-262 are
to be evaluated. The first TLV from range 260-262 is to be
interpreted as the primary node identifier, e.g. it acts as the
unique key by which the node can be referenced within its
administrative contexts. Any further TLVs are to be treated as
secondary identifiers, which may be used for cross-reference, but
are to be treated as if they are object attributes.
3.2.1.4. Router-ID Anchoring Example: ISO Pseudonode
IS-IS Pseudonodes are a good example for the variable Router-ID
anchoring. Consider Figure 12. This represents a Broadcast LAN
between a pair of routers. The "real" (=non pseudonode) routers have
both an IPv4 Router-ID and IS-IS Node-ID. The pseudonode does not
have an IPv4 Router-ID. Two unidirectional links (Node1, Pseudonode
1) and (Pseudonode 1, Node 2) are being generated.
The NRLI for (Node1, Pseudonode1) encodes local IPv4 router-ID, local
ISO node-ID and remote ISO node-id)
The NLRI for (Pseudonode1, Node2) encodes a local ISO node-ID and
remote ISO node-id.
+-----------------+ +-----------------+ +-----------------+
| Node1 | | Pseudonode 1 | | Node2 |
|1920.0000.2001.00|--->|1921.6800.1001.02|--->|1920.0000.2002.00|
| 192.0.2.1 | | | | 192.0.2.2 |
+-----------------+ +-----------------+ +-----------------+
Figure 12: IS-IS Pseudonodes
3.2.1.5. Router-ID Anchoring Example: OSPFv2 to IS-IS Migration
Migrating gracefully from one IGP to another requires congruent
operation of both routing protocols during the migration period. The
target protocol (IS-IS) supports more router-ID spaces than the
source (OSPFv2) protocol. When advertising a point-to-point link
between an OSPFv2-only router and an OSPFv2 and IS-IS enabled router
the following link information may be generated. Note that the IS-IS
router also supports the IPv6 traffic engineering extensions RFC 6119
[RFC6119] for IS-IS.
The NRLI encodes local IPv4 router-id, remote IPv4 router-id, remote
ISO node-id and remote IPv6 node-id.
Gredler, et al. Expires April 25, 2013 [Page 14]
Internet-Draft Link-State Info Distribution using BGP October 2012
3.2.2. Link Descriptors
The 'Link Descriptor' field is a set of Type/Length/Value (TLV)
triplets. The format of each TLV is shown in Section 3.1. The 'Link
descriptor' TLVs uniquely identify a link between a pair of anchor
Routers. A link described by the Link descriptor TLVs actually is a
"half-link", a unidirectional representation of a logical link. In
order to fully describe a single logical link two originating routers
need to advertise a half-link each, i.e. two link NLRIs will be
advertised.
The format and semantics of the 'value' fields in most 'Link
Descriptor' TLVs correspond to the format and semantics of value
fields in IS-IS Extended IS Reachability sub-TLVs, defined in
[RFC5305], [RFC5307] and [RFC6119]. Although the encodings for 'Link
Descriptor' TLVs were originally defined for IS-IS, the TLVs can
carry data sourced either by IS-IS or OSPF.
The following link descriptor TLVs are valid in the Link NLRI:
+------+------------------------+-----------------+-----------------+
| Type | Description | IS-IS | Value defined |
| | | TLV/Sub-TLV | in: |
+------+------------------------+-----------------+-----------------+
| 263 | Link Local/Remote | 22/4 | [RFC5307]/1.1 |
| | Identifiers | | |
| 264 | IPv4 interface address | 22/6 | [RFC5305]/3.2 |
| 265 | IPv4 neighbor address | 22/8 | [RFC5305]/3.3 |
| 266 | IPv6 interface address | 22/12 | [RFC6119]/4.2 |
| 267 | IPv6 neighbor address | 22/13 | [RFC6119]/4.3 |
| 268 | Multi Topology ID | --- | Section 3.2.2.1 |
+------+------------------------+-----------------+-----------------+
Table 2: Link Descriptor TLVs
3.2.2.1. Multi Topology ID TLV
The Multi Topology ID TLV (Type 268) carries the Multi Topology ID
for this link. The semantics of the Multi Topology ID are defined in
RFC5120, Section 7.2 [RFC5120], and the OSPF Multi Topology ID),
defined in RFC4915, Section 3.7 [RFC4915]. If the value in the Multi
Topology ID TLV is derived from OSPF, then the upper 9 bits of the
Multi Topology ID are set to 0.
Gredler, et al. Expires April 25, 2013 [Page 15]
Internet-Draft Link-State Info Distribution using BGP October 2012
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R R R R| Multi Topology ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Multi Topology ID TLV format
3.2.3. The Prefix NLRI
The Prefix NLRI is a variable length field that contains an IP
address prefix (IPv4 or IPv6) originally advertised in the IGP
topology. The distinction between IPv4 and IPv6 prefixes is given by
the NLRI Type filed in the Link State NLRI. Reachability information
is encoded as one or more 2-tuples of the form <length, prefix>,
whose fields are described below:
+---------------------------+
| Length (1 octet) |
+---------------------------+
| Prefix (variable) |
+---------------------------+
Figure 14: Prefix NLRI format
3.3. The LINK_STATE Attribute
This is an optional, transitive BGP attribute that is used to carry
link, node and prefix parameters and attributes. It is defined as a
set of Type/Length/Value (TLV) triplets, described in the following
section. This attribute SHOULD only be included with Link State
NLRIs. This attribute MUST be ignored for all other NLRIs.
3.3.1. Link Attribute TLVs
Each 'Link Attribute' is a Type/Length/Value (TLV) triplet formatted
as defined in Section 3.1. The format and semantics of the 'value'
fields in some 'Link Attribute' TLVs correspond to the format and
semantics of value fields in IS-IS Extended IS Reachability sub-TLVs,
defined in [RFC5305] and [RFC5307]. Other 'Link Attribute' TLVs are
defined in this document. Although the encodings for 'Link
Attribute' TLVs were originally defined for IS-IS, the TLVs can carry
data sourced either by IS-IS or OSPF.
The following 'Link Attribute' TLVs are are valid in the LINK_STATE
attribute:
Gredler, et al. Expires April 25, 2013 [Page 16]
Internet-Draft Link-State Info Distribution using BGP October 2012
+------+-------------------------+----------------+-----------------+
| Type | Description | IS-IS | Defined in: |
| | | TLV/Sub-TLV | |
+------+-------------------------+----------------+-----------------+
| 269 | Administrative group | 22/3 | [RFC5305]/3.1 |
| | (color) | | |
| 270 | Maximum link bandwidth | 22/9 | [RFC5305]/3.3 |
| 271 | Max. reservable link | 22/10 | [RFC5305]/3.5 |
| | bandwidth | | |
| 272 | Unreserved bandwidth | 22/11 | [RFC5305]/3.6 |
| 273 | Link Protection Type | 22/20 | [RFC5307]/1.2 |
| 274 | MPLS Protocol Mask | --- | Section 3.3.1.1 |
| 275 | Metric | --- | Section 3.3.1.2 |
| 276 | Shared Risk Link Group | --- | Section 3.3.1.3 |
| 277 | OSPF specific link | --- | Section 3.3.1.4 |
| | attribute | | |
| 278 | IS-IS Specific Link | --- | Section 3.3.1.5 |
| | Attribute | | |
| 279 | Area ID | --- | Section 3.3.1.6 |
+------+-------------------------+----------------+-----------------+
Table 3: Link Attribute TLVs
3.3.1.1. MPLS Protocol Mask TLV
The MPLS Protocol TLV (Type 274) carries a bit mask describing which
MPLS signaling protocols are enabled. The length of this TLV is 1.
The value is a bit array of 8 flags, where each bit represents an
MPLS Protocol capability.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L R |
+-+-+-+-+-+-+-+-+
Figure 15: MPLS Protocol TLV
The following bits are defined:
Gredler, et al. Expires April 25, 2013 [Page 17]
Internet-Draft Link-State Info Distribution using BGP October 2012
+-----+---------------------------------------------+-----------+
| Bit | Description | Reference |
+-----+---------------------------------------------+-----------+
| 0 | Label Distribution Protocol (LDP) | [RFC5036] |
| 1 | Extension to RSVP for LSP Tunnels (RSVP-TE) | [RFC3209] |
| 2-7 | Reserved for future use | |
+-----+---------------------------------------------+-----------+
Table 4: MPLS Protocol Mask TLV Codes
3.3.1.2. Metric TLV
The IGP Metric TLV (Type 275) carries the metric for this link. The
length of this TLV is 3. If the length of the metric from which the
IGP Metric value is derived is less than 3 (e.g. for OSPF link
metrics or non-wide IS-IS metric), then the upper bits of the TLV are
set to 0.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGP Link Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Metric TLV format
3.3.1.3. Shared Risk Link Group TLV
The Shared Risk Link Group (SRLG) TLV (Type 276) carries the Shared
Risk Link Group information (see Section 2.3, "Shared Risk Link Group
Information", of [RFC4202]). It contains a data structure consisting
of a (variable) list of SRLG values, where each element in the list
has 4 octets, as shown in Figure 17. The length of this TLV is 4 *
(number of SRLG values).
Gredler, et al. Expires April 25, 2013 [Page 18]
Internet-Draft Link-State Info Distribution using BGP October 2012
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ............ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Shared Risk Link Group TLV format
Note that there is no SRLG TLV in OSPF-TE. In IS-IS the SRLG
information is carried in two different TLVs: the IPv4 (SRLG) TLV
(Type 138) defined in [RFC5307], and the IPv6 SRLG TLV (Type 139)
defined in [RFC6119]. Since the Link State NLRI uses variable
Router-ID anchoring, both IPv4 and IPv6 SRLG information can be
carried in a single TLV.
3.3.1.4. OSPF Specific Link Attribute TLV
The OSPF specific link attribute TLV (Type 277) is an envelope that
transparently carries optional link properties TLVs advertised by an
OSPF router. The value field contains one or more optional OSPF link
attribute TLVs. An originating router shall use this TLV for
encoding information specific to the OSPF protocol or new OSPF
extensions for which there is no protocol neutral representation in
the BGP link-state NLRI.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| OSPF specific link attributes (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: OSPF specific link attribute format
3.3.1.5. IS-IS specific link attribute TLV
The IS-IS specific link attribute TLV (Type 278) is an envelope that
transparently carries optional link properties TLVs advertised by an
IS-IS router. The value field contains one or more optional IS-IS
Gredler, et al. Expires April 25, 2013 [Page 19]
Internet-Draft Link-State Info Distribution using BGP October 2012
link attribute TLVs. An originating router shall use this TLV for
encoding information specific to the IS-IS protocol or new IS-IS
extensions for which there is no protocol neutral representation in
the BGP link-state NLRI.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IS-IS specific link attributes (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: IS-IS specific link attribute format
3.3.1.6. Link Area TLV
The Area TLV (Type 279) carries the Area ID which is assigned on this
link. If a link is present in more than one Area then several
occurrences of this TLV may be generated. Since only the OSPF
protocol carries the notion of link specific areas, the Area ID has a
fixed length of 4 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: Link Area TLV format
3.3.2. Node Attribute TLVs
The following node attribute TLVs are defined:
Gredler, et al. Expires April 25, 2013 [Page 20]
Internet-Draft Link-State Info Distribution using BGP October 2012
+------+--------------------------------+----------+
| Type | Description | Length |
+------+--------------------------------+----------+
| 280 | Multi Topology | 2 |
| 281 | Node Flag Bits | 1 |
| 282 | OSPF Specific Node Properties | variable |
| 283 | IS-IS Specific Node Properties | variable |
| 284 | Node Area ID | variable |
+------+--------------------------------+----------+
Table 5: Node Attribute TLVs
3.3.2.1. Multi Topology Node TLV
The Multi Topology TLV (Type 280) carries the Multi Topology ID and
topology specific flags for this node. The format and semantics of
the 'value' field in the Multi Topology TLV is defined in RFC5120,
Section 7.1 [RFC5120]. If the value in the Multi Topology TLV is
derived from OSPF, then the upper 9 bits of the Multi Topology ID and
the 'O' and 'A' bits are set to 0.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O A R R| Multi Topology ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: Multi Topology Node TLV format
3.3.2.2. Node Flag Bits TLV
The Node Flag Bits TLV (Type 281) carries a bit mask describing node
attributes. The value is a bit array of 8 flags, where each bit
represents a node capability.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+
Figure 22: Node Flag Bits TLV format
The bits are defined as follows:
Gredler, et al. Expires April 25, 2013 [Page 21]
Internet-Draft Link-State Info Distribution using BGP October 2012
+-----+--------------+-----------+
| Bit | Description | Reference |
+-----+--------------+-----------+
| 0 | Overload Bit | [RFC1195] |
| 1 | Attached Bit | [RFC1195] |
| 2 | External Bit | [RFC2328] |
| 3 | ABR Bit | [RFC2328] |
+-----+--------------+-----------+
Table 6: Node Flag Bits Definitions
3.3.2.3. OSPF Specific Node Properties TLV
The OSPF Specific Node Properties TLV (Type 282) is an envelope that
transparently carries optional node properties TLVs advertised by an
OSPF router. The value field contains one or more optional OSPF node
property TLVs, such as the OSPF Router Informational Capabilities TLV
defined in [RFC4970], or the OSPF TE Node Capability Descriptor TLV
described in [RFC5073]. An originating router shall use this TLV for
encoding information specific to the OSPF protocol or new OSPF
extensions for which there is no protocol neutral representation in
the BGP link-state NLRI.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| OSPF specific node properties (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: OSPF specific Node property format
3.3.2.4. IS-IS Specific Node Properties TLV
The IS-IS Router Specific Node Properties TLV (Type 283) is an
envelope that transparently carries optional node specific TLVs
advertised by an IS-IS router. The value field contains one or more
optional IS-IS node property TLVs, such as the IS-IS TE Node
Capability Descriptor TLV described in [RFC5073]. An originating
router shall use this TLV for encoding information specific to the
IS-IS protocol or new IS-IS extensions for which there is no protocol
neutral representation in the BGP link-state NLRI.
Gredler, et al. Expires April 25, 2013 [Page 22]
Internet-Draft Link-State Info Distribution using BGP October 2012
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IS-IS specific node properties (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24: IS-IS specific Node property format
3.3.2.5. Area Node TLV
The Area TLV (Type 284) carries the Area ID which is assigned to this
node. If a node is present in more than one Area then several
occurrences of this TLV may be generated. Since only the IS-IS
protocol carries the notion of per-node areas, the Area ID has a
variable length of 1 to 20 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Area ID (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25: Area Node TLV format
3.3.3. Prefix Attributes TLVs
Prefixes are learned from the IGP topology (ISIS or OSPF) with a set
of IGP attributes (such as metric, route tags, route type, etc.) that
MUST be reflected into the LINK_STATE attribute. This section
describes the different attributes related to the IPv4/IPv6 prefixes.
Prefix Attributes TLVs SHOULD be used when advertising NLRI types 3
and 4 only. The following attributes TLVs are defined:
Gredler, et al. Expires April 25, 2013 [Page 23]
Internet-Draft Link-State Info Distribution using BGP October 2012
+------+-------------------------+--------+-----------+
| Type | Description | Length | Reference |
+------+-------------------------+--------+-----------+
| 285 | IGP Flags | 4 | |
| 286 | Route Tag | 4 | [RFC5130] |
| 287 | Extended Tag | 8 | [RFC5130] |
| 288 | Metric | 4 | [RFC5305] |
| 289 | OSPF Forwarding Address | 4 | [RFC2328] |
+------+-------------------------+--------+-----------+
Table 7: Prefix Attribute TLVs
3.3.3.1. IGP Flags TLV
IGP Flags TLV contains ISIS and OSPF flags and bits originally
assigned to the prefix. The IGP Flags TLV is encoded as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IGP Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 26: IGP Flag TLV format
where:
Type is 285
Length is 4
The following bits are defined according to the table here below:
+------+------------------+-----------+
| Bit | Description | Reference |
+------+------------------+-----------+
| 0 | ISIS Up/Down Bit | [RFC5305] |
| 1-3 | OSPF Route Type | [RFC2328] |
| 4-15 | RESERVED | |
+------+------------------+-----------+
Table 8: IGP Flag Bits Definitions
OSPF Route Type can be either: Intra-Area (0x1), Inter-Area (0x2),
External 1 (0x3), External 2 (0x4), NSSA (0x5) and is encoded in a 3
bits number. For prefixes learned from IS-IS, this field MUST to be
Gredler, et al. Expires April 25, 2013 [Page 24]
Internet-Draft Link-State Info Distribution using BGP October 2012
set to 0x0 on transmission.
3.3.3.2. Route Tag
Route Tag TLV carries the original IGP TAG (ISIS or OSPF) of the
prefix and is encoded as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 27: IGP Route TAG TLV format
where:
Type is 286
Length is 4
Route Tag contains the original tags as learned in the IGP topology.
3.3.3.3. Extended Route Tag
Extended Route Tag TLV carries the ISIS Extended Route TAG of the
prefix and is encoded as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Route Tag |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: Extended IGP Route TAG TLV format
where:
Type is 287
Length is 8
Extended Route Tag contains the original ISIS Extended Tag as learned
Gredler, et al. Expires April 25, 2013 [Page 25]
Internet-Draft Link-State Info Distribution using BGP October 2012
in the IGP topology.
3.3.3.4. Prefix Metric TLV
Prefix Metric TLV carries the metric of the prefix as known in the
IGP topology. The attribute is mandatory and can only appear once.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: Prefix Metric TLV Format
where:
Type is 288
Length is 4
3.3.3.5. OSPF Forwarding Address TLV
OSPF Forwarding Address TLV carries the OSPF forwarding address as
known in the original OSPF advertisement. Forwarding address can be
either IPv4 or IPv6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding Address (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 30: OSPF Forwarding Address TLV Format
where:
Type is 289
Length is 4 for an IPv4 forwarding address an 16 for an IPv6
forwarding address
Gredler, et al. Expires April 25, 2013 [Page 26]
Internet-Draft Link-State Info Distribution using BGP October 2012
3.4. BGP Next Hop Information
BGP link-state information for both IPv4 and IPv6 networks can be
carried over either an IPv4 BGP session, or an IPv6 BGP session. If
IPv4 BGP session is used, then the next hop in the MP_REACH_NLRI
SHOULD be an IPv4 address. Similarly, if IPv6 BGP session is used,
then the next hop in the MP_REACH_NLRI SHOULD be an IPv6 address.
Usually the next hop will be set to the local end-point address of
the BGP session. The next hop address MUST be encoded as described
in [RFC4760]. The length field of the next hop address will specify
the next hop address-family. If the next hop length is 4, then the
next hop is an IPv4 address; if the next hop length is 16, then it is
a global IPv6 address and if the next hop length is 32, then there is
one global IPv6 address followed by a link-local IPv6 address. The
link-local IPv6 address should be used as described in [RFC2545].
3.5. Inter-AS Links
The main source of TE information is the IGP, which is not active on
inter-AS links. In order to inject a non-IGP enabled link into the
BGP link-state RIB an implementation must support configuration of
static links.
4. Link to Path Aggregation
Distribution of all links available in the global Internet is
certainly possible, however not desirable from a scaling and privacy
point of view. Therefore an implementation may support link to path
aggregation. Rather than advertising all specific links of a domain,
an ASBR may advertise an "aggregate link" between a non-adjacent pair
of nodes. The "aggregate link" represents the aggregated set of link
properties between a pair of non-adjacent nodes. The actual methods
to compute the path properties (of bandwidth, metric) are outside the
scope of this document. The decision whether to advertise all
specific links or aggregated links is an operator's policy choice.
To highlight the varying levels of exposure, the following deployment
examples shall be discussed.
4.1. Example: No Link Aggregation
Consider Figure 31. Both AS1 and AS2 operators want to protect their
inter-AS {R1,R3}, {R2, R4} links using RSVP-FRR LSPs. If R1 wants to
compute its link-protection LSP to R3 it needs to "see" an alternate
path to R3. Therefore the AS2 operator exposes its topology. All
BGP TE enabled routers in AS1 "see" the full topology of AS and
therefore can compute a backup path. Note that the decision if the
direct link between {R3, R4} or the {R4, R5, R3) path is used is made
Gredler, et al. Expires April 25, 2013 [Page 27]
Internet-Draft Link-State Info Distribution using BGP October 2012
by the computing router.
AS1 : AS2
:
R1-------R3
| : | \
| : | R5
| : | /
R2-------R4
:
:
Figure 31: no-link-aggregation
4.2. Example: ASBR to ASBR Path Aggregation
The brief difference between the "no-link aggregation" example and
this example is that no specific link gets exposed. Consider
Figure 32. The only link which gets advertised by AS2 is an
"aggregate" link between R3 and R4. This is enough to tell AS1 that
there is a backup path. However the actual links being used are
hidden from the topology.
AS1 : AS2
:
R1-------R3
| : |
| : |
| : |
R2-------R4
:
:
Figure 32: asbr-link-aggregation
4.3. Example: Multi-AS Path Aggregation
Service providers in control of multiple ASes may even decide to not
expose their internal inter-AS links. Consider Figure 33. Rather
than exposing all specific R3 to R6 links, AS3 is modeled as a single
node which connects to the border routers of the aggregated domain.
Gredler, et al. Expires April 25, 2013 [Page 28]
Internet-Draft Link-State Info Distribution using BGP October 2012
AS1 : AS2 : AS3
: :
R1-------R3-----
| : : \
| : : vR0
| : : /
R2-------R4-----
: :
: :
Figure 33: multi-as-aggregation
5. IANA Considerations
This document requests a code point from the registry of Address
Family Numbers.
This document requests a code point from the BGP Path Attributes
registry.
This document requests creation of a new registry for node anchor,
link descriptor and link attribute TLVs. Values 0-255 are reserved.
Values 256-65535 will be used for Codepoints. The registry will be
initialized as shown in Table 2 and Table 3. Allocations within the
registry will require documentation of the proposed use of the
allocated value and approval by the Designated Expert assigned by the
IESG (see [RFC5226]).
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Manageability Considerations
This section is structured as recommended in [RFC5706].
6.1. Operational Considerations
6.1.1. Operations
Existing BGP operation procedures apply. No new operation procedures
are defined in this document. It shall be noted that the NLRI
information present in this document purely carries application level
data that have no immediate corresponding forwarding state impact.
As such, any churn in reachability information has different impact
than regular BGP update which needs to chaange forwarding state for
an entire router. Furthermore it is anticipated that distribution of
Gredler, et al. Expires April 25, 2013 [Page 29]
Internet-Draft Link-State Info Distribution using BGP October 2012
this NLRI will be handled by dedicated route-reflectors providing a
level of isolation and fault-containment between different NLRI
types.
6.1.2. Installation and Initial Setup
Configuration parameters defined in Section 6.2.3 SHOULD be
initialized to the following default values:
o The Link-State NLRI capability is turned off for all neighbors.
o The maximum rate at which Link State NLRIs will be advertised/
withdrawn from neighbors is set to 200 updates per second.
6.1.3. Migration Path
The proposed extension is only activated between BGP peers after
capability negotiation. Moreover, the extensions can be turned on/
off an individual peer basis (see Section 6.2.3), so the extension
can be gradually rolled out in the network.
6.1.4. Requirements on Other Protocols and Functional Components
The protocol extension defined in this document does not put new
requirements on other protocols or functional components.
6.1.5. Impact on Network Operation
Frequency of Link-State NLRI updates could interfere with regular BGP
prefix distribution. A network operator MAY use a dedicated Route-
Reflector infrastructure to distribute Link-State NLRIs.
Distribution of Link-State NLRIs SHOULD be limited to a single admin
domain, which can consist of multiple areas within an AS or multiple
ASes.
6.1.6. Verifying Correct Operation
Existing BGP procedures apply. In addition, an implementation SHOULD
allow an operator to:
o List neighbors with whom the Speaker is exchanging Link-State
NLRIs
Gredler, et al. Expires April 25, 2013 [Page 30]
Internet-Draft Link-State Info Distribution using BGP October 2012
6.2. Management Considerations
6.2.1. Management Information
6.2.2. Fault Management
TBD.
6.2.3. Configuration Management
An implementation SHOULD allow the operator to specify neighbors to
which Link-State NLRIs will be advertised and from which Link-State
NLRIs will be accepted.
An implementation SHOULD allow the operator to specify the maximum
rate at which Link State NLRIs will be advertised/withdrawn from
neighbors
An implementation SHOULD allow the operator to specify the maximum
rate at which Link State NLRIs will be accepted from neighbors
An implementation SHOULD allow the operator to specify the maximum
number of Link State NLRIs stored in router's RIB.
An implementation SHOULD allow the operator to create abstracted
topologies that are advertised to neighbors; Create different
abstractions for different neighbors.
6.2.4. Accounting Management
Not Applicable.
6.2.5. Performance Management
An implementation SHOULD provide the following statistics:
o Total number of Link-State NLRI updates sent/received
o Number of Link-State NLRI updates sent/received, per neighbor
o Number of errored received Link-State NLRI updates, per neighbor
o Total number of locally originated Link-State NLRIs
Gredler, et al. Expires April 25, 2013 [Page 31]
Internet-Draft Link-State Info Distribution using BGP October 2012
6.2.6. Security Management
An operator SHOULD define ACLs to limit inbound updates as follows:
o Drop all updates from Consumer peers
7. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the BGP security model.
A BGP Speaker SHOULD NOT accept updates from a Consumer peer.
An operator SHOULD employ a mechanism to protect a BGP Speaker
against DDOS attacks from Consumers.
8. Acknowledgements
We would like to thank Nischal Sheth, Alia Atlas, Robert Varga, David
Ward, Derek Yeung, Murtuza Lightwala, John Scudder, Kaliraj
Vairavakkalai, Les Ginsberg, Liem Nguyen, Manish Bhardwaj, Mike
Shand, Peter Psenak, Rex Fernando, Richard Woundy, Saikat Ray, Steven
Luong, Tamas Mondal, Waqas Alam, and Yakov Rekhter for their
comments.
9. References
9.1. Normative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
March 1999.
Gredler, et al. Expires April 25, 2013 [Page 32]
Internet-Draft Link-State Info Distribution using BGP October 2012
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
January 2007.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, June 2007.
[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065, August 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5130] Previdi, S., Shand, M., and C. Martin, "A Policy Control
Mechanism in IS-IS Using Administrative Tags", RFC 5130,
February 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5307] Kompella, K. and Y. Rekhter, "IS-IS Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)",
RFC 5307, October 2008.
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Gredler, et al. Expires April 25, 2013 [Page 33]
Internet-Draft Link-State Info Distribution using BGP October 2012
Engineering in IS-IS", RFC 6119, February 2011.
9.2. Informative References
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-13 (work in progress),
September 2012.
[I-D.ietf-isis-mi]
Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", draft-ietf-isis-mi-08 (work
in progress), October 2012.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
[RFC5073] Vasseur, J. and J. Le Roux, "IGP Routing Protocol
Extensions for Discovery of Traffic Engineering Node
Capabilities", RFC 5073, December 2007.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
Path Computation Method for Establishing Inter-Domain
Traffic Engineering (TE) Label Switched Paths (LSPs)",
RFC 5152, February 2008.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, November 2009.
[RFC6549] Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
Instance Extensions", RFC 6549, March 2012.
Gredler, et al. Expires April 25, 2013 [Page 34]
Internet-Draft Link-State Info Distribution using BGP October 2012
Authors' Addresses
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Jan Medved
Cisco Systems, Inc.
170, West Tasman Drive
San Jose, CA 95134
US
Email: jmedved@cisco.com
Stefano Previdi
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Adrian Farrel
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: afarrel@juniper.net
Saikat Ray
Cisco Systems, Inc.
170, West Tasman Drive
San Jose, CA 95134
US
Email: sairay@cisco.com
Gredler, et al. Expires April 25, 2013 [Page 35]
