Internet DRAFT - draft-ymbk-grow-wkc-behavior
draft-ymbk-grow-wkc-behavior
Network Working Group J. Borkenhagen
Internet-Draft AT&T
Intended status: Standards Track R. Bush
Expires: December 23, 2018 Internet Initiative Japan
R. Bonica
Juniper Networks
S. Bayraktar
Cisco Systems
June 21, 2018
Well-Known Community Policy Behavior
draft-ymbk-grow-wkc-behavior-03
Abstract
Well-Known BGP Communities are manipulated inconsistently by current
implementations. This results in difficulties for operators. It is
recommended that removal policies be applied consistently to Well-
Known Communities.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in RFC 2119 [RFC2119] only when they
appear in all upper case. They may also appear in lower or mixed
case as English words, without normative meaning.
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 December 23, 2018.
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Copyright Notice
Copyright (c) 2018 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Manipulation of Communities by Policy . . . . . . . . . . . . 3
3. Community Manipulation Policy Differences . . . . . . . . . . 3
4. Documentation of Vendor Implementations . . . . . . . . . . . 3
4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4
5. Note for Those Writing RFCs for New Community-Like
Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The BGP Communities Attribute was specified in [RFC1997] which
introduced the concept of Well-Known Communities. In hindsight, it
did not prescribe as fully as it should have how Well-Known
Communities may be manipulated by policies applied by operators.
Currently, implementations differ in this regard, and these
differences can result in inconsistent behaviors that operators find
difficult to identify and resolve.
This document describes the current behavioral differences in order
to assist operators in generating consistent community-manipulation
policies in a multi-vendor environment, and to prevent the
introduction of additional divergence in implementations.
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2. Manipulation of Communities by Policy
[RFC1997] says:
"A BGP speaker receiving a route with the COMMUNITIES path attribute
may modify this attribute according to the local policy."
A basic operational need is to add or remove one or more communities
to the received set. Another common need is to replace all received
communities with a new set. To simplify the second case, most BGP
policy implementations provide syntax to "set" community that
operators use to mean "remove any/all communities present on the
update received from the neighbor, and apply this set of communities
instead."
Some operators prefer to write explicit policy to delete unwanted
communities rather than using "set;" i.e. using a "delete community
*:*" and then "add community x:y ..." configuration statements in an
attempt to replace all received communities. The same community
manipulation policy differences described in the following section
exist in both "set" and "delete community *:*" syntax. For
simplicity, the remainder of this document refers only to the "set"
behaviors.
3. Community Manipulation Policy Differences
Vendor implementations differ in the treatment of certain Well-Known
communities when modified using the syntax to "set" the community.
Some replace all communities including the Well-Known ones with the
new set, while others replace all non-Well-Known Communities but do
not modify any Well-Known Communities that are present.
These differences result in what would appear to be identical policy
configurations having very different results on different platforms.
4. Documentation of Vendor Implementations
In Juniper Networks' JunOS, "community set" removes all received
communities, Well-Known or otherwise.
In Cisco Systems' IOS-XR, "set community" removes all received
communities except for the following:
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+-------------+-----------------------------------+
| Numeric | Common Name |
+-------------+-----------------------------------+
| 0:0 | internet |
| 65535:0 | graceful-shutdown |
| 65535:1 | accept-own rfc7611 |
| 65535:65281 | NO_EXPORT |
| 65535:65282 | NO_ADVERTISE |
| 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) |
+-------------+-----------------------------------+
Communities not removed by Cisco IOS/XR
Table 1
IOS-XR does allow Well-Known communities to be removed one at a time
by explicit policy; for example, "delete community accept-own".
Operators are advised to consult IOS-XR documentation and/or Cisco
Systems support for full details.
On Brocade NetIron: "set community X" removes all communities and
sets X.
In Huawei's VRP product, "community set" removes all received
communities, well-Known or otherwise.
In OpenBSD's OpenBGPD, "set community" does not remove any
communities, well-Known or otherwise.
4.1. Note on an Inconsistency
The IANA publishes a list of Well-Known Communities [IANA-WKS].
IOS-XR's set of well-known communities that "set community" will not
overwrite diverges from IANA's list. Quite a few well-known
communities from IANA's list do not receive special treatment in IOS-
XR, and at least one specific community on IOS-XR's special treatment
list (internet == 0:0) is not really on IANA's list -- it's taken
from the "Reserved" range [0x00000000-0x0000FFFF].
This merely notes an inconsistency. It is not a plea to 'protect'
the entire IANA list from "set community."
5. Note for Those Writing RFCs for New Community-Like Attributes
Care should be taken when establishing new [RFC1997]-like attributes
(large communities, wide communities, etc) to avoid repeating this
mistake.
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6. Action Items
Unfortunately, it would be operationally disruptive for vendors to
change their current implementations.
Vendors SHOULD share the behavior of their implementations for
inclusion in this document, especially if their behavior differs from
the examples described.
For new well-known communities specified (after this draft), vendors
MUST treat "community set" command to mean "remove all other
communities, Well-Known or otherwise."
7. Security Considerations
Surprising defaults and/or undocumented behaviors are not good for
security. This document attepts to remedy that.
8. IANA Considerations
This document has no IANA Considerations other than to be aware that
any future Well-Known Communities will be subject to the policy
treatment described here.
9. Acknowledgements
The authors thank Martijn Schmidt for his contribution, Qin Wu for
the Huawei data point.
10. Normative References
[IANA-WKS]
"IANA Well-Known Comunities",
<https://www.iana.org/assignments/bgp-well-known-
communities/bgp-well-known-communities.xhtml>.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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Authors' Addresses
Jay Borkenhagen
AT&T
200 Laurel Avenue South
Middletown, NJ 07748
United States of America
Email: jayb@att.com
Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, WA 98110
United States of America
Email: randy@psg.com
Ron Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
US
Email: rbonica@juniper.net
Serpil Bayraktar
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: serpil@cisco.com
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