draft-ietf-grow-wkc-behavior-04.txt   draft-ietf-grow-wkc-behavior-05.txt 
Network Working Group J. Borkenhagen Network Working Group J. Borkenhagen
Internet-Draft AT&T Internet-Draft AT&T
Intended status: Best Current Practice R. Bush Updates: 1997 (if approved) R. Bush
Expires: November 17, 2019 Internet Initiative Japan Intended status: Standards Track Internet Initiative Japan
R. Bonica Expires: December 1, 2019 R. Bonica
Juniper Networks Juniper Networks
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
May 16, 2019 May 30, 2019
Well-Known Community Policy Behavior Well-Known Community Policy Behavior
draft-ietf-grow-wkc-behavior-04 draft-ietf-grow-wkc-behavior-05
Abstract Abstract
Popular BGP implementations manipulate Well-known Communities Well-Known BGP Communities are manipulated differently across various
differently from one another. This results in difficulties for current implementations; resulting in difficulties for operators.
operators. Network operators are encouraged to deploy consistent Network operators should deploy consistent community handling across
community handling across their networks, taking the inconsistent their networks while taking the inconsistent behaviors from the
behaviors from the various BGP implementations they operate into various BGP implementations into consideration.. This document
consideration. This document recommends specific action items to recommends specific actions to limit future inconsistency, namely BGP
limit future inconsistency, namely BGP implementors are expected to implementors must not create further inconsistencies from this point
not create any further inconsistencies from this point forward. forward.
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 Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 1, 2019.
This Internet-Draft will expire on November 17, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Manipulation of Communities by Policy . . . . . . . . . . . . 3
3. Manipulation of Communities by Policy . . . . . . . . . . . . 3 3. Community Manipulation Policy Differences . . . . . . . . . . 3
4. Community Manipulation Policy Differences . . . . . . . . . . 3 4. Documentation of Vendor Implementations . . . . . . . . . . . 3
5. Documentation of Vendor Implementations . . . . . . . . . . . 4 4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4
5.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 5 5. Note for Those Writing RFCs for New Community-Like Attributes 5
6. Note for Those Writing RFCs for New Community-Like Attributes 5 6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 10. Normative References . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6
11.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
The BGP Communities Attribute was specified in [RFC1997] which The BGP Communities Attribute was specified in [RFC1997] which
introduced the concept of Well-Known Communities. In hindsight, introduced the concept of Well-Known Communities. In hindsight,
[RFC1997] did not prescribe as fully as it should have how Well-Known [RFC1997] did not prescribe as fully as it should have how Well-Known
Communities may be manipulated by policies applied by operators. Communities may be manipulated by policies applied by operators.
Currently, implementations differ in this regard, and these Currently, implementations differ in this regard, and these
differences can result in inconsistent behaviors that operators find differences can result in inconsistent behaviors that operators find
difficult to identify and resolve. difficult to identify and resolve.
This document describes the current behavioral differences in order This document describes the current behavioral differences in order
to assist operators in generating consistent community-manipulation to assist operators in generating consistent community-manipulation
policies in a multi-vendor environment, and to prevent the policies in a multi-vendor environment, and to prevent the
introduction of additional divergence in implementations. introduction of additional divergence in implementations.
This document recommends specific action items to limit future This document recommends specific actions to limit future
inconsistency. inconsistency, namely BGP implementors MUST NOT create further
inconsistencies from this point forward.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Manipulation of Communities by Policy 2. Manipulation of Communities by Policy
[RFC1997] says: [RFC1997] says:
"A BGP speaker receiving a route with the COMMUNITIES path attribute "A BGP speaker receiving a route with the COMMUNITIES path attribute
may modify this attribute according to the local policy." may modify this attribute according to the local policy."
One basic operational need is to add or remove one or more One basic operational need is to add or remove one or more
communities to the received set. The focus of this document is communities to the set. The focus of this document is another common
another common operational need, to replace all communities with a operational need, to replace all communities with a new set. To
new set. To simplify this second case, most BGP policy simplify this second case, most BGP policy implementations provide
implementations provide syntax to "set" community that operators use syntax to "set" community that operators use to mean "remove any/all
to mean "remove any/all communities present on the route, and apply communities present on the route, and apply this set of communities
this set of communities instead." instead."
Some operators prefer to write explicit policy to delete unwanted Some operators prefer to write explicit policy to delete unwanted
communities rather than using "set;" i.e. using a "delete community communities rather than using "set;" i.e. using a "delete community
*:*" and then "add community x:y ..." configuration statements in an *:*" and then "add community x:y ..." configuration statements in an
attempt to replace all received communities. The same community attempt to replace all communities. The same community manipulation
manipulation policy differences described in the following section policy differences described in the following section exist in both
exist in both "set" and "delete community *:*" syntax. For "set" and "delete community *:*" syntax. For simplicity, the
simplicity, the remainder of this document refers only to the "set" remainder of this document refers only to the "set" behaviors, which
behaviors, which we refer to collectively as each implementation's we refer to collectively as each implementation's '"set" directive.'
'"set" directive.'
4. Community Manipulation Policy Differences 3. Community Manipulation Policy Differences
Vendor implementations differ in the treatment of certain Well-Known Vendor implementations differ in the treatment of certain Well-Known
communities when modified using the syntax to "set" the community. communities when modified using the syntax to "set" the community.
Some replace all communities including the Well-Known ones with the Some replace all communities including the Well-Known ones with the
new set, while others replace all non-Well-Known Communities but do new set, while others replace all non-Well-Known Communities but do
not modify any Well-Known Communities that are present. not modify any Well-Known Communities that are present.
These differences result in what would appear to be identical policy These differences result in what would appear to be identical policy
configurations having very different results on different platforms. configurations having very different results on different platforms.
5. Documentation of Vendor Implementations 4. Documentation of Vendor Implementations
In this section we document the syntax and observed behavior of the In this section we document the syntax and observed behavior of the
"set" directive in several popular BGP implementations. "set" directive in several popular BGP implementations to illustrate
the severity of the problem operators face.
In Juniper Networks' Junos OS, "community set" removes all received In Juniper Networks' Junos OS, "community set" removes all
communities, Well-Known or otherwise. communities, Well-Known or otherwise.
In Cisco Systems' IOS XR, "set community" removes all received In Cisco IOS XR, "set community" removes all communities except for
communities except for the following: the following:
+-------------+-----------------------------------+ +-------------+-----------------------------------+
| Numeric | Common Name | | Numeric | Common Name |
+-------------+-----------------------------------+ +-------------+-----------------------------------+
| 0:0 | internet | | 0:0 | internet |
| 65535:0 | graceful-shutdown | | 65535:0 | graceful-shutdown |
| 65535:1 | accept-own rfc7611 | | 65535:1 | accept-own rfc7611 |
| 65535:65281 | NO_EXPORT | | 65535:65281 | NO_EXPORT |
| 65535:65282 | NO_ADVERTISE | | 65535:65282 | NO_ADVERTISE |
| 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) | | 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) |
+-------------+-----------------------------------+ +-------------+-----------------------------------+
Communities not removed by Cisco IOS XR Communities not removed by Cisco IOS XR
Table 1 Table 1
IOS XR does allow Well-Known communities to be removed by explicitly Cisco IOS XR does allow Well-Known communities to be removed only by
enumerating each one, not in the aggregate; for example, "delete explicitly enumerating one at a time, not in the aggregate; for
community accept-own". Operators are advised to consult IOS XR example, "delete community accept-own". Operators are advised to
documentation and/or Cisco Systems support for full details. consult Cisco IOS XR documentation and/or Cisco support for full
details.
On Extreme networks' Brocade NetIron: "set community X" removes all On Extreme networks' Brocade NetIron: "set community X" removes all
received communities and sets X. communities and sets X.
In Huawei's VRP product, "community set" removes all received In Huawei's VRP product, "community set" removes all communities,
communities, well-Known or otherwise. Well-Known or otherwise.
In OpenBSD's OpenBGPD, "set community" does not remove any In OpenBGPD, "set community" does not remove any communities, Well-
communities, Well-Known or otherwise. Known or otherwise.
Nokia's SR OS has several directives that operate on communities. Nokia's SR OS has several directives that operate on communities.
Its "set" directive is called using the "replace" keyword, replacing Its "set" directive is called using the "replace" keyword, replacing
all received communities, Well-Known or otherwise, with the specified all communities, Well-Known or otherwise, with the specified
communities. communities.
5.1. Note on an Inconsistency 4.1. Note on an Inconsistency
In IOS XR, "set community" will not overwrite some well-known The IANA publishes a list of Well-Known Communities [IANA-WKC].
communities. However, it will overwrite other well-known
communities. Conversely, In IOS XR, "set community" will not Cisco IOS XR's set of Well-Known communities that "set community"
overwrite some communities that are not well-known (e.g., (internet will not overwrite diverges from the IANA's list of Well-Known
== 0:0). communities. Quite a few Well-Known communities from IANA's list do
not receive special treatment in Cisco IOS XR, and at least one
specific community on Cisco 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' This merely notes an inconsistency. It is not a plea to 'protect'
the entire IANA list from "set community." the entire IANA list from "set community."
6. Note for Those Writing RFCs for New Community-Like Attributes 5. Note for Those Writing RFCs for New Community-Like Attributes
When establishing new [RFC1997]-like attributes (large communities, > When establishing new [RFC1997]-like attributes (large communities,
wide communities, etc.), RFC authors should state how the new wide communities, etc.), RFC authors should state explicitly how the
community attribute is to be handled. > new attribute is to be handled.
7. Action Items 6. Action Items
Network operators are encouraged to limit their use of the "set" Network operators are encouraged to limit their use of the "set"
directive (within reason), to improve the readability of their directive (within reason), to improve consistency across platforms.
configurations and hopefully to achieve behavioral consistency across
platforms.
Unfortunately, it would be operationally disruptive for vendors to Unfortunately, it would be operationally disruptive for vendors to
change their current implementations. change their current implementations.
Vendors SHOULD clearly document the behavior of "set" directive in Vendors SHOULD clearly document the behavior of "set" directive in
their implementations. their implementations.
Vendors MUST ensure that their implementations' "set" directive Vendors MUST ensure that their implementations' "set" directive
treatment of any specific community does not change if/when that treatment of any specific community does not change if/when that
community becomes a new Well-Known Community through future community becomes a new Well-Known Community through future
skipping to change at page 6, line 5 skipping to change at page 5, line 42
implementations where the "set" directive removes no communities, implementations where the "set" directive removes no communities,
that behavior MUST continue. that behavior MUST continue.
Given the implementation inconsistencies described in this document, Given the implementation inconsistencies described in this document,
network operators are urged never to rely on any implicit network operators are urged never to rely on any implicit
understanding of a neighbor ASN's BGP community handling. I.e., understanding of a neighbor ASN's BGP community handling. I.e.,
before announcing prefixes with NO_EXPORT or any other community to a before announcing prefixes with NO_EXPORT or any other community to a
neighbor ASN, the operator should confirm with that neighbor how the neighbor ASN, the operator should confirm with that neighbor how the
community will be treated. community will be treated.
8. Security Considerations 7. Security Considerations
Surprising defaults and/or undocumented behaviors are not good for Surprising defaults and/or undocumented behaviors are not good for
security. This document attempts to remedy that. security. This document attempts to remedy that.
Also see Appendix A of [RFC5706]. 8. IANA Considerations
9. IANA Considerations
This document has no IANA Considerations. This document has no IANA Considerations; though the IANA may wish to
refer to this document, if/when published, in [IANA-WKC].
10. Acknowledgments 9. Acknowledgments
The authors thank Martijn Schmidt, Qin Wu for the Huawei data point, The authors thank Martijn Schmidt, Qin Wu for the Huawei data point,
Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob
Heitz. Heitz.
11. References 10. Normative References
11.1. Normative References [IANA-WKC]
IANA, "Border Gateway Protocol (BGP) Well-Known
Communities", <https://www.iana.org/assignments/
bgp-well-known-communities>.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>. <http://www.rfc-editor.org/info/rfc1997>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
Authors' Addresses Authors' Addresses
Jay Borkenhagen Jay Borkenhagen
AT&T AT&T
200 Laurel Avenue South 200 Laurel Avenue South
Middletown, NJ 07748 Middletown, NJ 07748
United States of America United States of America
Email: jayb@att.com Email: jayb@att.com
Randy Bush Randy Bush
Internet Initiative Japan Internet Initiative Japan
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