BGP TE attribute: BGP Traffic Engineering Attribute
A new optional BGP attribute that lets VPN routes carry the traffic engineering details of a link.
Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP Traffic Engineering Attribute", RFC 5543, DOI 10.17487/RFC5543, May 2009, <https://www.rfc-editor.org/info/rfc5543>.
@misc{rfc5543,
series = {Request for Comments},
number = 5543,
howpublished = {RFC 5543},
publisher = {RFC Editor},
doi = {10.17487/RFC5543},
url = {https://www.rfc-editor.org/info/rfc5543},
author = {H. Ould-Brahim and D. Fedyk and Y. Rekhter},
title = {{BGP Traffic Engineering Attribute}},
pagetotal = 6,
year = 2009,
month = may,
} RFC text
Contents
Network Working Group H. Ould-Brahim
Request for Comments: 5543 Nortel Networks
Category: Standards Track D. Fedyk
Alcatel-Lucent
Y. Rekhter
Juniper Networks
May 2009
BGP Traffic Engineering Attribute
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
This document defines a new BGP attribute, the Traffic Engineering
attribute, that enables BGP to carry Traffic Engineering information.
The scope and applicability of this attribute currently excludes its
use for non-VPN reachability information.
1. Introduction
In certain cases (e.g., Layer-1 VPNs (L1VPNs) [RFC5195]), it may be
useful to augment the VPN reachability information carried in BGP
with Traffic Engineering information.
This document defines a new BGP attribute, the Traffic Engineering
attribute, that enables BGP [RFC4271] to carry Traffic Engineering
information.
Section 4 of [RFC5195] describes one possible usage of this
attribute.
The scope and applicability of this attribute currently excludes its
use for non-VPN reachability information.
Procedures for modifying the Traffic Engineering attribute, when
re-advertising a route that carries such an attribute, are outside
the scope of this document.
2. Specification of Requirements
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].
3. Traffic Engineering Attribute
The Traffic Engineering attribute is an optional, non-transitive BGP
attribute.
The information carried in this attribute is identical to what is
carried in the Interface Switching Capability Descriptor, as
specified in [RFC4203] and [RFC5307].
The attribute contains one or more of the following:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Switching Cap | Encoding | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max LSP Bandwidth at priority 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Switching Capability specific information |
| (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Switching Capability (Switching Cap) field contains one of the
values specified in Section 3.1.1 of [RFC3471].
The Encoding field contains one of the values specified in Section
3.1.1 of [RFC3471].
The Reserved field SHOULD be set to 0 on transmit and MUST be ignored
on receive.
Maximum LSP (Label Switched Path) Bandwidth is encoded as a list of
eight 4-octet fields in the IEEE floating point format [IEEE], with
priority 0 first and priority 7 last. The units are bytes (not
bits!) per second.
The content of the Switching Capability specific information field
depends on the value of the Switching Capability field.
When the Switching Capability field is PSC-1, PSC-2, PSC-3, or PSC-4,
the Switching Capability specific information field includes Minimum
LSP Bandwidth and Interface MTU.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum LSP Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Minimum LSP Bandwidth is encoded in a 4-octet field in the IEEE
floating point format. The units are bytes (not bits!) per second.
Interface MTU is encoded as a 2-octet integer.
When the Switching Capability field is Layer-2 Switch Capable (L2SC),
there is no Switching Capability specific information field present.
When the Switching Capability field is Time-Division-Multiplex (TDM)
capable, the Switching Capability specific information field includes
Minimum LSP Bandwidth and an indication of whether the interface
supports Standard or Arbitrary SONET/SDH (Synchronous Optical
Network / Synchronous Digital Hierarchy).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum LSP Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Indication |
+-+-+-+-+-+-+-+-+
Minimum LSP Bandwidth is encoded in a 4-octet field in the IEEE
floating point format. The units are bytes (not bits!) per second.
The indication of whether the interface supports Standard or
Arbitrary SONET/SDH is encoded as 1 octet. The value of this octet
is 0 if the interface supports Standard SONET/SDH, and 1 if the
interface supports Arbitrary SONET/SDH.
When the Switching Capability field is Lambda Switch Capable (LSC),
there is no Switching Capability specific information field present.
4. Implication on Aggregation
Routes that carry the Traffic Engineering attribute have additional
semantics that could affect traffic-forwarding behavior. Therefore,
such routes SHALL NOT be aggregated unless they share identical
Traffic Engineering attributes.
Constructing the Traffic Engineering attribute when aggregating
routes with identical Traffic Engineering attributes follows the
procedure of [RFC4201].
5. Implication on Scalability
The use of the Traffic Engineering attribute does not increase the
number of routes, but may increase the number of BGP Update messages
required to distribute the routes, depending on whether or not these
routes share the same BGP Traffic Engineering attribute (see below).
When the routes differ other than in the Traffic Engineering
attribute (e.g., differ in the set of Route Targets and/or NEXT_HOP),
use of the Traffic Engineering attribute has no impact on the number
of BGP Update messages required to carry the routes. There is also
no impact when routes share all other attribute information and have
an aggregated or identical Traffic Engineering attribute. When
routes share all other attribute information and have different
Traffic Engineering attributes, routes must be distributed in
per-route BGP Update messages, rather than in a single message.
6. IANA Considerations
This document defines a new BGP attribute, Traffic Engineering. This
attribute is optional and non-transitive.
7. Security Considerations
This extension to BGP does not change the underlying security issues
currently inherent in BGP. BGP security considerations are discussed
in RFC 4271.
8. Acknowledgements
The authors would like to thank John Scudder and Jeffrey Haas for
their review and comments.
9. References
9.1. Normative References
[IEEE] IEEE, "IEEE Standard for Binary Floating-Point Arithmetic",
Standard 754-1985, 1985 (ISBN 1-5593-7653-8).
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling in
MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border
Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.
9.2. Informative References
[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC5195] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
Auto-Discovery for Layer-1 VPNs", RFC 5195, June 2008.
[RFC5307] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
Authors' Addresses
Hamid Ould-Brahim
Nortel Networks
EMail: hbrahim@nortel.com
Don Fedyk
Alcatel-Lucent
EMail: donald.fedyk@alcatel-lucent.com
Phone: 978-467-5645
Yakov Rekhter
Juniper Networks, Inc.
EMail: yakov@juniper.net
AI ELI5
On this page
§1Why BGP Needs a Traffic Engineering Attribute
In certain cases, for example Layer-1 VPNs (RFC 5195), it is useful to add Traffic Engineering information to the VPN reachability information that BGP already carries. RFC 5543 defines a new BGP attribute for this, so that BGP (RFC 4271) can carry that information.
The scope is deliberately narrow. The attribute currently may not be used for non-VPN reachability information. The procedures for modifying the attribute when a route that carries it is re-advertised are outside the scope of the document.
Sometimes a route announcement needs a note saying how much traffic the path can handle. This RFC adds a place to write that note, but only for private network services.
§2The Attribute and Its Fixed Fields
The Traffic Engineering attribute is an optional, non-transitive BGP attribute. The information inside is identical to what is carried in the Interface Switching Capability Descriptor defined in RFC 4203 and RFC 5307. The attribute holds one or more of these descriptors.
Each starts with a Switching Capability byte and an Encoding byte, both taking values from Section 3.1.1 of RFC 3471, then a 16-bit Reserved field. The reserved field SHOULD be set to 0 on transmit and MUST be ignored on receive.
Next come eight 4-octet Max LSP Bandwidth fields, for priority 0 first through priority 7 last. They use the IEEE floating point format, and the units are bytes (not bits) per second.
Each note starts with what kind of road it is, then lists the biggest load it can take for each of eight levels of importance.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
SWITCHING-CAP | Switching Cap | 1 byte | A Switching Capability value from Section 3.1.1 of RFC 3471. | |
ENCODING | Encoding | 1 byte | An Encoding value from Section 3.1.1 of RFC 3471. | |
RESERVED | Reserved | 2 bytes | SHOULD be 0 on transmit, MUST be ignored on receive. | |
BW-0 | Max LSP Bandwidth, priority 0 | 4 bytes | IEEE floating point, bytes per second. | |
BW-1 | Max LSP Bandwidth, priority 1 | 4 bytes | IEEE floating point, bytes per second. | |
BW-2 | Max LSP Bandwidth, priority 2 | 4 bytes | IEEE floating point, bytes per second. | |
BW-3 | Max LSP Bandwidth, priority 3 | 4 bytes | IEEE floating point, bytes per second. | |
BW-4 | Max LSP Bandwidth, priority 4 | 4 bytes | IEEE floating point, bytes per second. | |
BW-5 | Max LSP Bandwidth, priority 5 | 4 bytes | IEEE floating point, bytes per second. | |
BW-6 | Max LSP Bandwidth, priority 6 | 4 bytes | IEEE floating point, bytes per second. | |
BW-7 | Max LSP Bandwidth, priority 7 | 4 bytes | IEEE floating point, bytes per second. |
§3Switching Capability Specific Information
The last part of each descriptor is variable and depends on the Switching Capability field.
- For PSC-1, PSC-2, PSC-3 or PSC-4, it holds a 4-octet Minimum LSP Bandwidth and a 2-octet Interface MTU.
- For Layer-2 Switch Capable (L2SC), there is no specific information.
- For Time-Division-Multiplex (TDM) capable, it holds a 4-octet Minimum LSP Bandwidth and a 1-octet indication of Standard or Arbitrary SONET/SDH. The value is 0 for Standard and 1 for Arbitrary.
- For Lambda Switch Capable (LSC), there is no specific information.
Minimum LSP Bandwidth uses the same IEEE floating point format, in bytes per second. Interface MTU is a 2-octet integer.
After the main part, some kinds of road add extra details, like the smallest load allowed. Other kinds need nothing extra.
| Switching Capability | Specific information |
|---|---|
| PSC-1 to PSC-4 | Minimum LSP Bandwidth (4 octets) and Interface MTU (2 octets) |
| L2SC | None |
| TDM | Minimum LSP Bandwidth (4 octets) and Standard (0) or Arbitrary (1) SONET/SDH indication (1 octet) |
| LSC | None |
§4Effect on Route Aggregation
Routes that carry the attribute have extra semantics that could affect how traffic is forwarded. Because of that, such routes SHALL NOT be aggregated unless they share identical Traffic Engineering attributes.
When routes with identical attributes are aggregated, the attribute for the aggregate is built following the procedure of RFC 4201.
You can only merge two route announcements into one if their notes about the road match exactly.
§5Effect on Scalability
Using the attribute does not increase the number of routes, but it may increase the number of BGP Update messages needed to distribute them. That depends on whether the routes share the same attribute.
If routes differ in other ways, such as their Route Targets or NEXT_HOP, there is no impact on the number of Update messages. There is also no impact when routes share all other attribute information and have an aggregated or identical Traffic Engineering attribute. When routes share all other attribute information but have different Traffic Engineering attributes, they must be sent in per-route Update messages rather than in a single message.
If every route has a different note, they cannot travel in one big envelope, so more envelopes are needed.
§6IANA and Security Considerations
IANA is told that this document defines a new BGP attribute named Traffic Engineering, which is optional and non-transitive.
On security, the extension does not change the underlying security issues already inherent in BGP. BGP security considerations are discussed in RFC 4271.
Adding the note does not make BGP any safer or any riskier than it already was.