< draft-ietf-grow-wkc-behavior-03.txt   draft-ietf-grow-wkc-behavior-04.txt >
Network Working Group J. Borkenhagen Network Working Group J. Borkenhagen
Internet-Draft AT&T Internet-Draft AT&T
Intended status: Standards Track R. Bush Intended status: Best Current Practice R. Bush
Expires: September 11, 2019 Internet Initiative Japan Expires: November 17, 2019 Internet Initiative Japan
R. Bonica R. Bonica
Juniper Networks Juniper Networks
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
March 10, 2019 May 16, 2019
Well-Known Community Policy Behavior Well-Known Community Policy Behavior
draft-ietf-grow-wkc-behavior-03 draft-ietf-grow-wkc-behavior-04
Abstract Abstract
Well-Known BGP Communities are manipulated inconsistently by current Popular BGP implementations manipulate Well-known Communities
implementations. This results in difficulties for operators. differently from one another. This results in difficulties for
Network operators are encouraged to deploy consistent community operators. Network operators are encouraged to deploy consistent
handling across their networks, taking the inconsistent behaviors community handling across their networks, taking the inconsistent
from the various BGP implementations they operate into consideration. behaviors from the various BGP implementations they operate into
Also, BGP implementors are expected to not create any further consideration. This document recommends specific action items to
inconsistencies from this point forward. limit future inconsistency, namely BGP implementors are expected to
not create any further inconsistencies from this point 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
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Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 September 11, 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.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Manipulation of Communities by Policy . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Community Manipulation Policy Differences . . . . . . . . . . 3 3. Manipulation of Communities by Policy . . . . . . . . . . . . 3
4. Documentation of Vendor Implementations . . . . . . . . . . . 3 4. Community Manipulation Policy Differences . . . . . . . . . . 3
4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4 5. Documentation of Vendor Implementations . . . . . . . . . . . 4
5. Note for Those Writing RFCs for New Community-Like Attributes 5 5.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 5
6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Note for Those Writing RFCs for New Community-Like Attributes 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Normative References . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 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.
2. Manipulation of Communities by Policy This document recommends specific action items to limit future
inconsistency.
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
[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 received set. The focus of this document is
another common operational need, to replace all communities with a another common operational need, to replace all communities with a
new set. To simplify this second case, most BGP policy new set. To simplify this second case, most BGP policy
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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 received communities. The same community
manipulation policy differences described in the following section manipulation policy differences described in the following section
exist in both "set" and "delete community *:*" syntax. For exist in both "set" and "delete community *:*" syntax. For
simplicity, the remainder of this document refers only to the "set" simplicity, the remainder of this document refers only to the "set"
behaviors, which we refer to collectively as each implementation's behaviors, which we refer to collectively as each implementation's
'"set" directive.' '"set" directive.'
3. Community Manipulation Policy Differences 4. 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.
4. Documentation of Vendor Implementations 5. 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.
In Juniper Networks' Junos OS, "community set" removes all received In Juniper Networks' Junos OS, "community set" removes all received
communities, Well-Known or otherwise. communities, Well-Known or otherwise.
In Cisco Systems' IOS XR, "set community" removes all received In Cisco Systems' IOS XR, "set community" removes all received
communities except for the following: communities except for the following:
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| 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 one at a time IOS XR does allow Well-Known communities to be removed by explicitly
by explicit policy; for example, "delete community accept-own". enumerating each one, not in the aggregate; for example, "delete
Operators are advised to consult IOS XR documentation and/or Cisco community accept-own". Operators are advised to consult IOS XR
Systems support for full details. documentation and/or Cisco Systems support for full details.
On Extreme networks' Brocade NetIron: "set community X" removes all On Extreme networks' Brocade NetIron: "set community X" removes all
communities and sets X. received communities and sets X.
In Huawei's VRP product, "community set" removes all received In Huawei's VRP product, "community set" removes all received
communities, well-Known or otherwise. communities, well-Known or otherwise.
In OpenBSD's OpenBGPD, "set community" does not remove any In OpenBSD's OpenBGPD, "set community" does not remove any
communities, Well-Known or otherwise. communities, Well-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 communities, Well-Known or otherwise, with the specified all received communities, Well-Known or otherwise, with the specified
communities. communities.
4.1. Note on an Inconsistency 5.1. 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 In IOS XR, "set community" will not overwrite some well-known
overwrite diverges from IANA's list. Quite a few well-known communities. However, it will overwrite other well-known
communities from IANA's list do not receive special treatment in IOS communities. Conversely, In IOS XR, "set community" will not
XR, and at least one specific community on IOS XR's special treatment overwrite some communities that are not well-known (e.g., (internet
list (internet == 0:0) is not really on IANA's list -- it's taken == 0:0).
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."
5. Note for Those Writing RFCs for New Community-Like Attributes 6. Note for Those Writing RFCs for New Community-Like Attributes
Care should be taken when establishing new [RFC1997]-like attributes When establishing new [RFC1997]-like attributes (large communities,
(large communities, wide communities, etc) to avoid repeating this wide communities, etc.), RFC authors should state how the new
mistake. community attribute is to be handled.
6. Action Items 7. Action Items
Network operators are encouraged to limit their use of the "set"
directive (within reason), to improve the readability of their
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
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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.
Network operators are encouraged to limit their use of the "set" 8. Security Considerations
directive (within reason), to improve the readability of their
configurations and hopefully to achieve behavioral consistency across
platforms.
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.
8. IANA Considerations Also see Appendix A of [RFC5706].
This document has no IANA Considerations other than to be aware that 9. IANA Considerations
any future Well-Known Communities will be subject to the policy
treatment described here.
9. Acknowledgments This document has no IANA Considerations.
10. 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.
10. Normative References 11. References
[IANA-WKS] 11.1. Normative References
"IANA Well-Known Communities",
<https://www.iana.org/assignments/bgp-well-known-
communities/bgp-well-known-communities.xhtml>.
[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,
<http://www.rfc-editor.org/info/rfc1997>. <https://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,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
Authors' Addresses [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
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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