Inter-Domain Routing H. Gredler
Internet-Draft J. Medved
Intended status: Standards Track Juniper Networks, Inc.
Expires: September 4, 2011 March 3, 2011
Advertising Traffic Engineering Information in BGP
draft-gredler-bgp-te-00
Abstract
This document defines a new Border Gateway Protocol Network Layer
Reachability Information (BGP NLRI) encoding format that can be used
to distribute Traffic Engineering (TE) link information. Links can
be either physical links connecting physical nodes, or virtual paths
between physical or abstract nodes. The TE information is carried
via the BGP, thereby reusing protocol algorithms, operational
experience, and administrative processes, such as inter-provider
peering agreements.
The BGP protocol carrying Traffic Engineering (TE) information would
provide a well-defined, uniform, policy-controlled interface from the
network to outside servers that need to learn the network topology in
real-time, for example an ALTO Server or a Path Computation Server.
Having TE information from remote areas and/or Autonomous Systems
would allow path computation for inter-area and/or inter-AS source-
routed unicast and multicast tunnels.
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/.
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."
Gredler & Medved Expires September 4, 2011 [Page 1]
Internet-Draft TE Information in BGP March 2011
This Internet-Draft will expire on September 4, 2011.
Copyright Notice
Copyright (c) 2011 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 & Medved Expires September 4, 2011 [Page 2]
Internet-Draft TE Information in BGP March 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Transcoding TE Link Information Into a BGP NLRI . . . . . . . 5
3.1. TLV Format . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Node anchors . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Router-ID Anchoring Example: ISO Pseudonode . . . . . 8
3.2.2. Router-ID Anchoring Example: OSPFv2 to IS-IS
Migration . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Link Descriptors . . . . . . . . . . . . . . . . . . . . . 8
3.4. Link Attributes . . . . . . . . . . . . . . . . . . . . . 9
3.4.1. TE Default Metric TLV . . . . . . . . . . . . . . . . 10
3.4.2. IGP Link Metric TLV . . . . . . . . . . . . . . . . . 10
3.4.3. Shared Risk Link Group TLV . . . . . . . . . . . . . . 11
3.5. IGP Area Information . . . . . . . . . . . . . . . . . . . 11
3.6. Inter-AS Links . . . . . . . . . . . . . . . . . . . . . . 12
4. Link to Path Aggregation . . . . . . . . . . . . . . . . . . . 12
4.1. Example: No Link Aggregation . . . . . . . . . . . . . . . 12
4.2. Example: ASBR to ASBR Path Aggregation . . . . . . . . . . 13
4.3. Example: Multi-AS Path Aggregation . . . . . . . . . . . . 13
5. Originating the TED NLRI . . . . . . . . . . . . . . . . . . . 13
6. Receiving the TED NLRI . . . . . . . . . . . . . . . . . . . . 14
7. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. MPLS TE . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.2. ALTO Server Network API . . . . . . . . . . . . . . . . . 15
7.3. Path Computation Element (PCE) TED Synchronization
Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Gredler & Medved Expires September 4, 2011 [Page 3]
Internet-Draft TE Information in BGP March 2011
1. Introduction
Today, the contents of the traffic engineering database usually has
the scope of an IGP area. There are several use cases that could
benefit from knowing the topology or Traffic Engineering (TE) data in
a remote area or Autonomous System, but today no mechanism exists to
distribute this information beyond an IGP area. This draft proposes
to use BGP as the distribution mechanism for traffic engineering data
between routers in different IGP areas and/or Autonomous Systems.
The mechanism can also be used to exchange topology and TE data
between the network and external network-aware applications, such as
the Alto Servers.
The Border Gateway Protocol (BGP [RFC4271]) has grown beyond its
original intention of disseminating IPv4 Inter-domain routing paths.
A modern BGP implementation can be viewed as a ubiquitous database
replication mechanism, which allows replication of many different
state information types across arbitrary distribution graphs. Its
built-in loop protection mechanism (AS path, Cluster List attributes)
enables building of stable and redundant distribution topologies. In
addition to IP routing, applications that use BGP for state
distribution are L2VPN, VPLS, MAC-VPN, Route-target information, and
Flowspec for firewalling. Using BGP as a dissemination protocol for
Traffic Engineering data is a logical consequence.
A router maintains a database for storing Traffic Engineering related
data and link information. The Traffic Engineering Database (TED) is
populated by a link-state IGP routing protocol that supports TE
extensions: IS-IS or OSPF. The TED can be seen as a protocol-neutral
representation of links in the area. Link attributes stored in the
TED are: local/remote IP addresses, local/remote interface indices,
metric, link bandwidth, reservable bandwidth, per CoS class
reservation state, preemption and Shared Risk Link Groups (SRLG).
The router's BGP process can retrieve the TE data from the TED
database and distribute it to peer BGP Speakers using the encoding
specified in this draft.
A BGP Speaker may distribute the real physical topology from the TED,
or 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.
Consumers of the TE data are peer routers in other areas either in
the router's own AS or in remote ASes, or entities outside the
network that may need network and/or TE data to optimize their
behavior.
Gredler & Medved Expires September 4, 2011 [Page 4]
Internet-Draft TE Information in BGP March 2011
2. Scope
The scope of TED NLRI are the static attributes / metrics of a path
between two routers. The path can be a physical link or multiple
links aggregated into a path. Dynamic data, such as dynamic
bandwidth or delay metrics, is out of scope of this draft.
3. Transcoding TE Link Information Into a BGP NLRI
The MP_REACH and MP_UNREACH attributes are BGP's containers for
carrying opaque information. Each TED NLRI describes a single link
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 anchoring Router-IDs are carried in the Node Anchor TLVs.
All TE link information shall be encoded using a TBD AFI / SAFI 1 or
SAFI 128 header into those attributes. SAFI 1 shall be used for
Internet routing (Public) and SAFI 128 shall be used for VPN routing
(Private) applications.
In order for two BGP speakers to exchange TE 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 (multiprotocol BGP), with an
AFI of TBD and an SAFI of 1 or 128.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Link Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Anchors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attributes (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: TED SAFI 1 NLRI Format
Gredler & Medved Expires September 4, 2011 [Page 5]
Internet-Draft TE Information in BGP March 2011
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Link Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Route Distinguisher +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Anchors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Descriptors (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attributes (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: TED SAFI 128 NLRI Format
The 'Total Link Length" field contains the cumulative length of all
the TLVs, describing the Node Anchors, Link descriptors and Link
Attributes. For VPN applications it also includes the length of the
Route Distinguisher.
3.1. TLV Format
The Node anchor, Link descriptor and Link attribute fields are
described using a set of Type/Length/Value triplets. The format of
each TLV is shown in Figure 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: 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 & Medved Expires September 4, 2011 [Page 6]
Internet-Draft TE Information in BGP March 2011
3.2. Node anchors
The set of Node Anchor TLVs describes which Protocols Router-IDs will
be following to "anchor" the link described by the "Link attribute
TLVs". There must be at least one "like" router-ID pair per-
protocol. If a peer sends an illegal combination in this respect,
then this is handled as an NLRI error, described in [RFC4760].
+------+--------------------------+--------+
| Type | Description | Length |
+------+--------------------------+--------+
| 256 | Local Autonomous System | 4 |
| 257 | Local IPv4 Router-ID | 4 |
| 258 | Local IPv6 Router-ID | 16 |
| 259 | Local ISO Node-ID | 7 |
| 260 | Remote Autonomous System | 4 |
| 261 | Remote IPv4 Router-ID | 4 |
| 262 | Remote IPv6 Router-ID | 16 |
| 263 | Remote ISO Node-ID | 7 |
+------+--------------------------+--------+
Table 1: Node Anchor TLVs
Local IPv4 Router ID: opaque value (can be an IPv4 address or an 32
Bit router ID)
Remote IPv4 Router ID: opaque value (can be an IPv4 address or 32
Bit router ID)
Local IPv6 Router ID: opaque value (can be an IPv6 address or 128
Bit router ID)
Remote IPv6 Router ID: opaque value (can be an IPv6 address or 128
Bit router ID)
Local ISO Node ID: ISO node-ID (6 octets ISO system-ID plus PSN
octet)
Remote ISO Node ID: ISO node-ID (6 octets ISO system-ID plus PSN
octet)
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 may be
included in the NLRI. The Local and Remote Autonomous System TLVs
Gredler & Medved Expires September 4, 2011 [Page 7]
Internet-Draft TE Information in BGP March 2011
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. Router-ID Anchoring Example: ISO Pseudonode
IS-IS Pseudonodes are a good example for the variable Router-ID
anchoring. Consider Figure 4. 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, remote
IPv4 router-ID and remote ISO node-id.
+-----------------+ +-----------------+ +-----------------+
| Node1 | | Pseudonode 1 | | Node2 |
|1921.6800.1001.00|--->|1921.6800.1001.02|--->|1921.6800.1002.00|
| 192.168.1.1 | | | | 192.168.1.2 |
+-----------------+ +-----------------+ +-----------------+
Figure 4: IS-IS Pseudonodes
3.2.2. 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) does support 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 does encode local IPv4 router-id, remote IPv4 router-id,
remote ISO node-id and remote IPv6 node-id.
3.3. Link Descriptors
The 'Link Descriptor' field is a set of Type/Length/Value (TLV)
triplets. The format of each TLV is shown in Figure 3. The 'Link
descriptor' TLVs uniquely identify a link between a pair of anchor
Routers.
The encoding of 'Link Descriptor' TLVs, i.e. the Codepoints in
Gredler & Medved Expires September 4, 2011 [Page 8]
Internet-Draft TE Information in BGP March 2011
'Type', and the 'Length' and 'Value' fields are the same as defined
in [RFC5305], [RFC5307], and [RFC6119] for sub-TLVs in the Extended
IS reachability TLV. The Codepoints are in the IANA Protocol
Registry for IS-IS, sub-TLV Codepoints for TLV 22, [IANA-ISIS].
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 TED NLRI:
+------+-------------------------------+------------------------+
| Type | Description | Defined in: |
+------+-------------------------------+------------------------+
| 4 | Link Local/Remote Identifiers | [RFC5307], Section 1.1 |
| 6 | IPv4 interface address | [RFC5305], Section 3.2 |
| 8 | IPv4 neighbor address | [RFC5305], Section 3.3 |
| 12 | IPv6 interface address | [RFC6119], Section 4.2 |
| 13 | IPv6 neighbor address | [RFC6119], Section 4.3 |
+------+-------------------------------+------------------------+
Table 2: Link Descriptor TLVs
3.4. Link Attributes
The 'Link Attributes' field is a set of Type/Length/Value (TLV)
triplets. The format of each TLV is shown in Figure 3.
For Codepoints < 255, the encoding of 'Link Attributes' TLVs, i.e.
the Codepoints in 'Type', and the 'Length' and 'Value' fields are the
same as defined in [RFC5305], [RFC5307], and [RFC6119] for sub-TLVs
in the Extended IS reachability TLV. The Codepoints are in the IANA
Protocol Registry for IS-IS, sub-TLV Codepoints for TLV 22,
[IANA-ISIS]. Although the encodings for 'Link Attributes' TLVs were
originally defined for IS-IS, the TLVs can carry data sourced either
by IS-IS or OSPF.
For Codepoints > 255, the encoding of 'Link Attributes' TLVs is
described in subsequent sections.
The following link attribute TLVs are valid in the TED NLRI:
Gredler & Medved Expires September 4, 2011 [Page 9]
Internet-Draft TE Information in BGP March 2011
+-------+--------------------------------+------------------------+
| Type | Description | Defined in: |
+-------+--------------------------------+------------------------+
| 3 | Administrative group (color) | [RFC5305], Section 3.1 |
| 9 | Maximum link bandwidth | [RFC5305], Section 3.3 |
| 10 | Max. reservable link bandwidth | [RFC5305], Section 3.5 |
| 11 | Unreserved bandwidth | [RFC5305], Section 3.6 |
| 20 | Link Protection Type | [RFC5307], Section 1.2 |
| 64512 | TE Default Metric | Section 3.4.1 |
| 64513 | IGP Link Metric | Section 3.4.2 |
| 64514 | Shared Risk Link Group | Section 3.4.3 |
+-------+--------------------------------+------------------------+
Table 3: Link Attribute TLVs
3.4.1. TE Default Metric TLV
The TE Default Metric TLV (Type 64512) carries the TE Default metric
for this link. This TLV corresponds to the IS-IS TE Default metric
sub-TLV (Type 18), defined in RFC5305, Section 3.7 [RFC5305], and the
OSPF TE Metric sub-TLV (Type 5), defined in RFC3630, Section 2.5.5
[RFC3630]. If the value in the TE Default metric TLV is derived from
IS-IS TE Default Metric, then the upper 8 bits of this 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE Default Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: TE Default metric TLV format
3.4.2. IGP Link Metric TLV
The IGP Metric TLV (Type 64513) carries the IGP metric for this link.
This attribute is only present if the IGP link metric is different
from the TE Default Metric (Type 18). The length of this TLV is 3.
If the length of the IGP link 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.
Gredler & Medved Expires September 4, 2011 [Page 10]
Internet-Draft TE Information in BGP March 2011
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 6: IGP Link Metric TLV format
3.4.3. Shared Risk Link Group TLV
The Shared Risk Link Group (SRLG) TLV (Type 64514) 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 7. The length of this TLV is 4 *
(number of SRLG values).
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 7: 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 BGP TED NLRI uses variable Router-ID
anchoring, both IPv4 and IPv6 SRLG information can be carried in a
single TLV.
3.5. IGP Area Information
IGP Area information can be carried in BGP communities. An
implementation should support configuration that maps IGP areas to
BGP communities.
Gredler & Medved Expires September 4, 2011 [Page 11]
Internet-Draft TE Information in BGP March 2011
3.6. 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
traffic-engineering database (TED) an implementation must support
configuration of static TE 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 8. 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
by the computing router.
AS1 : AS2
:
R1-------R3
| : | \
| : | R5
| : | /
R2-------R4
:
:
Figure 8: no-link-aggregation
Gredler & Medved Expires September 4, 2011 [Page 12]
Internet-Draft TE Information in BGP March 2011
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 9. 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 9: 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 10. 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.
AS1 : AS2 : AS3
: :
R1-------R3-----
| : : \
| : : vR0
| : : /
R2-------R4-----
: :
: :
Figure 10: multi-as-aggregation
5. Originating the TED NLRI
A BGP Speaker must be configured to originate TED NLRIs. Usually
export of the TED database into BGP is enabled on ASBRs and ABRs.
The BGP Speaker shall throttle the rate of TED NLRI updates. An
implementation shall provide a configuration attribute for the
Gredler & Medved Expires September 4, 2011 [Page 13]
Internet-Draft TE Information in BGP March 2011
interval between updates. The minimum interval between updates is 30
seconds.
6. Receiving the TED NLRI
This section describes the processing of TED NLRIs at the receiving
BGP Speaker.
TE attributes for a link received from an IGP have higher priority
than TED NLRIs received via BGP. Multiple BGP Speakers may advertise
the same TED NLRI; the receiving BGP Speaker can individually choose
the source BGP Speaker for each NLRI.
The AS_PATH attribute is used both for loop detection and for NLRI
selection: the TED NLRI with shorter AS_PATH length is preferred.
The Community and Extended Community path attributes are stored in
the RIB and may be used in operator-defined policies. Communities
can also be used to encode the IGP Area information. All other path
attributes are ignored.
7. Use Cases
7.1. MPLS TE
If a router wants to compute a MPLS TE path across IGP areas TED
lacks visibility of the complete topology. This is an issue for
large scale networks that need to segment their core networks into
distinct areas because inter-area TE cannot get deployed there.
Current solutions for inter area TE only compute the path for the
first area. The router only has full topological visibility for the
first area along the path, but not for subsequent areas. The best
practice is to use a technique called "loose-hop-expansion" which
uses the IGP computed shortest path topology for the remainder of the
path. Therefore no non-SPF based path setup is possible across
areas. This has disadvantages for path protection and path
engineering applications, as shown in Figure 11.
Gredler & Medved Expires September 4, 2011 [Page 14]
Internet-Draft TE Information in BGP March 2011
............................... ...................................
: Area 51 : : Area 0 :
: +--------+ +--------+ +--------+ :
: ************************************************************ :
: * +-------| R1 |-----| ABR1 |-----| R3 |-------+ * :
: * | ######## | | # | | | | * :
: * | # +--------+ +----|-#-+ +--------+ | * :
: +-*-|-#-+ : :| # +---|-*-+ :
: | * # | : :| # | * | :
: | S # | : :| # | D | :
: | # | : :| # | | :
: +---|-#-+ : :| # +---|---+ :
: | # +--------+ +----|-#-+ +--------+ | :
: | ############################# | | | | :
: +-------| R2 |-----| ABR2 |-----| R4 |-------+ :
: | | | | | | :
: +--------+ +--------+ +--------+ :
: : : :
:.............................: :.................................:
......
**** Primary LSP : : Area Boundary
#### Bypass LSP :....:
Figure 11: MPLS TE Bypass LSP problem
Router S sets up an RSVP LSP from S to D. Although it has only
visibility into Area 51, the LSP setup ultimately succeeds, as
shortest path first routing from ABR1 onwards routes the RSVP message
towards destination D. What does not work is to setup a Link
Protection bypass LSP protection for the R1 to ABR1 link as shown in
the figure. The problem is that the TE database at Router R1 does
not have path visibility of the link between ABR1 and ABR2, such that
it can compute the Link Bypass LSP.
7.2. ALTO Server Network API
An ALTO Server 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: the network map that specifies allocation of prefixes to PIDs,
and the cost map that specifies the cost between the PIDs. 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
Gredler & Medved Expires September 4, 2011 [Page 15]
Internet-Draft TE Information in BGP March 2011
prefix and TE data are required: prefix data is required to generate
the network maps, TE (topology) data is required to generate the cost
maps. Prefix data is carried and originated in BGP, TE data is
originated and carried in an IGP. Without BGP TE NLRI the ALTO
Server would have to peer with both BGP Speakers and IGP in multiple
areas and/or ASes to obtain all the necessary network topology data.
The BGP TE NLRI allows for a single interface between the network and
the ALTO Server.
7.3. Path Computation Element (PCE) TED Synchronization Protocol
RFC4655, Section 5.2, Figure 2 [RFC4655] describes a Path Computation
Element (PCE) which synchronizes its traffic engineering database
(TED) by use of a routing protocol. This memo describes the first
standardized protocol for PCE to learn about inter-AS or inter-area
TE information.
8. IANA Considerations
This document requests a code point from the registry of Address
Family Numbers
This document requests creation of a new registry for node anchor,
link descriptor and link attribute TLVs. The range of Codepoints in
the registry is 0-65535. Values 0-255 will shadow Codepoints of the
IANA Protocol Registry for IS-IS, sub-TLV Codepoints for TLV 22.
Values 256-65535 will be used for Codepoints that are specific to the
BGP TE NLRI. 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.
9. Security Considerations
This draft does not affect the BGP security model.
10. Acknowledgements
We would like to thank Alia Atlas, David Ward, John Scudder, Kaliraj
Vairavakkalai, Nischal Sheth and Yakov Rekhter from Juniper Networks,
Inc. and Richard Woundy from Comcast for their invaluable input and
comments.
Gredler & Medved Expires September 4, 2011 [Page 16]
Internet-Draft TE Information in BGP March 2011
11. References
11.1. Normative References
[IANA-ISIS]
"IS-IS TLV Codepoint, Sub-TLVs for TLV 22", <http://
www.iana.org/assignments/isis-tlv-codepoints/
isis-tlv-codepoints.xml#isis-tlv-codepoints-3>.
[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.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[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.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 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.
[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.
Gredler & Medved Expires September 4, 2011 [Page 17]
Internet-Draft TE Information in BGP March 2011
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", RFC 6119, February 2011.
11.2. Informative References
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-06 (work in progress),
October 2010.
Authors' Addresses
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Jan Medved
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: jmedved@juniper.net
Gredler & Medved Expires September 4, 2011 [Page 18]