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Versions: 00 01 02 03 draft-ietf-grow-wkc-behavior

Network Working Group                                     J. Borkenhagen
Internet-Draft                                                      AT&T
Intended status: Standards Track                                 R. Bush
Expires: December 13, 2018                     Internet Initiative Japan
                                                               R. Bonica
                                                        Juniper Networks
                                                            S. Bayraktar
                                                           Cisco Systems
                                                           June 11, 2018


                  Well-Known Community Policy Behavior
                    draft-ymbk-grow-wkc-behavior-02

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 13, 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
   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

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."

   One common operational need is to add or remove one or more
   communities to the current set.  Another common need is to replace
   all received communities with a new set as defined by policy.  All
   BGP policy implementations we know of provide syntax to "set" a
   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."

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:

            +-------------+-----------------------------------+
            | 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



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   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, "community set" removes no 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.

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."





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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>.

Authors' Addresses

   Jay Borkenhagen
   AT&T
   200 Laurel Avenue South
   Middletown, NJ  07748
   United States of America

   Email: jayb@att.com










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   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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