Network Working Group P. Mohapatra
Internet-Draft Sproute Networks
Intended status: Standards Track R. Fernando
Expires: 4 September 2025 Cisco Systems
R. Das, Ed.
Juniper Networks, Inc.
S. Mohanty, Ed.
Zscaler
M. Mishra
Cisco Systems
R.J. Szarecki
Google LLC
3 March 2025
BGP Link Bandwidth Extended Community
draft-ietf-idr-link-bandwidth-11
Abstract
This document describes an application of BGP extended communities
that allows a router to perform unequal cost load balancing.
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 [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 https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 September 2025.
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Copyright Notice
Copyright (c) 2025 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 (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Link Bandwidth Extended Community . . . . . . . . . . . . . . 3
3. Protocol Procedures . . . . . . . . . . . . . . . . . . . . . 4
3.1. Sender (Originating Link Bandwidth Community) . . . . . . 4
3.2. Receiver (Receiving Link Bandwidth Community) . . . . . . 4
3.3. Re-advertisement Procedures . . . . . . . . . . . . . . . 4
3.3.1. Re-advertisement with Next hop Self . . . . . . . . . 4
3.3.2. Re-advertisement with Next Hop Unchanged . . . . . . 5
3.4. Link Bandwidth Community Arithmetic and BGP Multipath . . 5
4. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 5
5. Document History . . . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
10. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Load balancing is a critical aspect of network design, enabling
efficient utilization of available bandwidth and improving overall
network performance. Traditional equal-cost multi-path (ECMP)
routing does not account for the varying capacities of different
paths. This document suggests that the external link bandwidth be
carried in the network using one of two new extended communities
[RFC4360] - the transitive and non-transitive link bandwidth extended
community. The Link Bandwidth Extended Community provides a
mechanism for routers to advertise the bandwidth of their downstream
path(s), facilitating maximum utilization of network resources.
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2. Link Bandwidth Extended Community
The Link Bandwidth Extended Communities are defined as a BGP extended
community that carries the bandwidth information of a router,
represented by BGP Protocol Next Hop, connecting to remote network.
This community can be used to inform other routers about the
available bandwidth on through a given route.
The Link bandwidth extended communities can be either transitive or
non-transitive. Therefore the value of the high-order octet of the
extended Type Field can be 0x00 or 0x40, respectively. The value of
the low-order octet of the extended type field for this communities
is 0x04. The value of the Global Administrator subfield in the Value
Field SHOULD represent the Autonomous System of the router that
attaches the Link Bandwidth Community, but it can be set to any
2-byte value. If the Autonomous System number cannot be represented
in two octets, as enabled by [RFC6793], AS_TRANS should be used in
the Global Administrator subfield. The bandwidth of the link is
expressed as 4 octets in [IEEE.754-2019] floating point format, units
being bytes (not bits!) per second. It is carried in the Local
Administrator subfield of the Value Field.
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=0x00/0x40 | SubType= 0x04 | AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Bandwidth Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1-octet field MUST be set to 0x00 or 0x40
to indicate transitive/non-transitive.
SubType: 1-octet field MUST be set to 0x04
to indicate 'Link-Bandwidth'.
Global Administrator sub-field:
2-octet represent the Autonomous System.
Local Administrator sub-field:
Bandwidth value (bytes per sec) encoded as 4 octets
in IEEE floating point format.
Figure 1: Link Bandwidth Extended Community
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3. Protocol Procedures
3.1. Sender (Originating Link Bandwidth Community)
An originator of the link bandwidth community SHOULD be able to
originate either a transitive or a non-transitive link bandwidth
extended community. Implementations SHOULD provide configuration to
set the transitivity type of the link bandwidth community, as well as
the Global Administrator and bandwidth values in (Local Administrator
field), using local policy. No more than one link bandwidth extended
community SHALL be attached to a route.
The link bandwidth extended community MAY be attached or updated for
a BGP route upon receipt during Adj-RIB-In processing. The link
bandwidth extended community MAY be attached or updated for a BGP
route's Adj-RIB-Out entry while being advertised to a neighboring BGP
speaker.
Note: Implementations MAY provide a configuration option to send non-
transitive link bandwidth extended communities on external BGP
sessions.
3.2. Receiver (Receiving Link Bandwidth Community)
A BGP receiver MUST be able to process link bandwidth extended
community of both transitive and non-transitive types. The receiver
MUST NOT flap or treat the route as malformed based on the
transitivity of the link bandwidth extended community and/or BGP
session type (internal vs. external).
Note: Implementations MAY provide configuration to accept non-
transitive link bandwidth extended communities from external BGP
sessions.
3.3. Re-advertisement Procedures
3.3.1. Re-advertisement with Next hop Self
When a BGP speaker re-advertises a route with the link bandwidth
extended community and sets the next hop to itself, it SHOULD follow
the same procedures as outlined in Section 3.1.
In the absence of any import or export policies that alter the Link
Bandwidth Extended Community, any received Link Bandwidth extended
community on the route will be re-advertised unchanged, in accordance
with standard BGP procedures.
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3.3.2. Re-advertisement with Next Hop Unchanged
A BGP speaker that receives a route with the link bandwidth
community, re-advertises or reflects the same without changing its
next hop, SHOULD NOT change the link bandwidth extended community in
any way.
3.4. Link Bandwidth Community Arithmetic and BGP Multipath
In a BGP multipath ECMP environment, the value of the link bandwidth
community that is sent or re-advertised may be calculated based on
the link bandwidth communities of the routes contributing to
multipath in the Local Routing Information Base (Local-RIB). This
topic is beyond the scope of this document.
4. Error Handling
If a receiver receives a route with more than one Link Bandwidth
Extended Community, it SHOULD:
* Prefer the lowest value of the attached link bandwidth community,
irrespective of the extended community's transitivity.
* Prefer the transitive link bandwidth extended community when
choosing between transitive and non-transitive types that have the
same value.
Implementations MAY provide configuration to change the above
preferences.
Link bandwidth extended communities with a negative value SHALL be
ignored and MUST NOT be originated.
WECMP (Weighted Equal-Cost Multi-Path) can be utilized when only all
contributing paths have a non-zero value in the link bandwidth
extended community. If any of the paths lack a valid link bandwidth
extended community, ECMP (Equal-Cost Multi-Path) MUST be used
instead.
5. Document History
The BGP Link Bandwidth Extended Community has evolved over several
versions of the IETF draft. In the earlier versions up to draft-
ietf-idr-link-bandwidth-08, only the non-transitive version of the
link bandwidth extended community was supported. However, starting
from draft-ietf-idr-link-bandwidth-09, both transitive and non-
transitive versions of the link bandwidth extended community are
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supported.
An old sender/receiver is a BGP speaker that uses procedures up to
draft (https://datatracker.ietf.org/doc/html/draft-ietf-idr-link-
bandwidth-08) or any undocumented behavior for link bandwidth
extended community.
A new sender/receiver is a BGP speaker that implements procedures
specified in this document.
Receiving BGP speakers need to be upgraded to support the procedures
defined in this document to provide full interoperability for both
transitive and non-transitive versions of the link bandwidth extended
community. In order simplify implementations, it is not a goal to
provide interoperability between old Receivers and new Senders.
6. IANA Considerations
This document defines a specific application of the two-octet AS
specific extended community.
IANA is requested to update the Transitive Two-Octet AS-Specific
Extended Community Sub-Types registry (Type 0x00) and Sub-Type 0x04
to:
Name
----
transitive Link Bandwidth Ext. Community
IANA is requested to update the Non-Transitive Two-Octet AS-Specific
Extended Community Sub-Types registry (Type 0x40) and Sub-Type 0x04
to:
Name
----
non-transitive Link Bandwidth Ext. Community
Both updates are to Reference this document.
7. Security Considerations
There are no additional security risks introduced by this design.
8. Contributors
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Kaliraj Vairavakkalai
Juniper Networks, Inc.
1133 Innovation Way,
Sunnyvale, CA 94089
United States of America
Email: kaliraj@juniper.net
Natrajan Venkataraman
Juniper Networks, Inc.
1133 Innovation Way,
Sunnyvale, CA 94089
United States of America
Email: natv@juniper.net
9. Acknowledgments
The authors would like to thank Yakov Rekhter, Srihari Sangli and Dan
Tappan for proposing unequal cost load balancing as one possible
application of the extended community attribute.
The authors would like to thank Bruno Decraene, Robert Raszuk, Joel
Halpern, Aleksi Suhonen, Randy Bush, Jeff Haas, Stephane Litkowski,
Serge Krier and John Scudder for their comments and contributions.
10. Normative References
[IEEE.754-2019]
IEEE, "IEEE Standard for Floating-Point Arithmetic", 22
July 2019, <https://ieeexplore.ieee.org/document/8766229>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/info/rfc6793>.
Authors' Addresses
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Pradosh Mohapatra
Sproute Networks
Email: pradosh@sproute.com
Rex Fernando
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: rex@cisco.com
Reshma Das (editor)
Juniper Networks, Inc.
1133 Innovation Way,
Sunnyvale, CA 94089
United States of America
Email: dreshma@juniper.net
Satya Mohanty (editor)
Zscaler
120 Holger Way,
San Jose, CA 95134
United States of America
Email: smohanty@zscaler.com
Mankamana Mishra
Cisco Systems
821 alder drive,
Milpitas, CA 95035
United States of America
Email: mankamis@cisco.com
Rafal Jan Szarecki
Google LLC
1160 N Mathilda Ave,
Sunnyvale, CA 94089
United States of America
Email: rszarecki@gmail.com
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