--- 1/draft-ietf-grow-wkc-behavior-02.txt 2019-03-10 18:13:10.618792987 -0700 +++ 2/draft-ietf-grow-wkc-behavior-03.txt 2019-03-10 18:13:10.638793473 -0700 @@ -1,32 +1,32 @@ Network Working Group J. Borkenhagen Internet-Draft AT&T Intended status: Standards Track R. Bush -Expires: July 26, 2019 Internet Initiative Japan +Expires: September 11, 2019 Internet Initiative Japan R. Bonica Juniper Networks S. Bayraktar Cisco Systems - January 22, 2019 + March 10, 2019 Well-Known Community Policy Behavior - draft-ietf-grow-wkc-behavior-02 + draft-ietf-grow-wkc-behavior-03 Abstract Well-Known BGP Communities are manipulated inconsistently by current implementations. This results in difficulties for operators. Network operators are encouraged to deploy consistent community handling across their networks, taking the inconsistent behaviors - from the various bgp implementations they operate into consideration. - Also, bgp implementors are expected to not create any further + from the various BGP implementations they operate into consideration. + Also, 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. @@ -38,21 +38,21 @@ 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 July 26, 2019. + This Internet-Draft will expire on September 11, 2019. Copyright Notice Copyright (c) 2019 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 @@ -62,27 +62,26 @@ 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 + 5. Note for Those Writing RFCs for New Community-Like Attributes 5 6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 - 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 - 10. Normative References . . . . . . . . . . . . . . . . . . . . 5 + 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 + 10. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction The BGP Communities Attribute was specified in [RFC1997] which introduced the concept of Well-Known Communities. In hindsight, [RFC1997] 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 @@ -93,151 +92,163 @@ policies in a multi-vendor environment, and to prevent the introduction of additional divergence in implementations. 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." + One basic operational need is to add or remove one or more + communities to the received set. The focus of this document is + another common operational need, to replace all communities with a + new set. To simplify this second case, most BGP policy + implementations provide syntax to "set" community that operators use + to mean "remove any/all communities present on the route, 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. + behaviors, which we refer to collectively as each implementation's + '"set" directive.' 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 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, "community set" removes all received + In Juniper Networks' Junos OS, "community set" removes all received 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: +-------------+-----------------------------------+ | 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 + Communities not removed by Cisco IOS XR 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 one at a time by explicit policy; for example, "delete community accept-own". - Operators are advised to consult IOS-XR documentation and/or Cisco + 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. + On Extreme networks' 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. + Nokia's SR OS has several directives that operate on communities. + Its "set" directive is called using the "replace" keyword, replacing + all communities, Well-Known or otherwise, with the specified + communities. + 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 + 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 + 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 clearly document the behavior of "set" directive in their implementations. - Vendors MUST ensure that any Well-Known Communities specified after - this document's publication are removed by their "set" directive. + Vendors MUST ensure that their implementations' "set" directive + treatment of any specific community does not change if/when that + community becomes a new Well-Known Community through future + standardization. For most implementations, this means that the "set" + directive MUST continue to remove the community; for those + implementations where the "set" directive removes no communities, + that behavior MUST continue. Given the implementation inconsistencies described in this document, 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 neighbor ASN, the operator should confirm with that neighbor how the community will be treated. 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. 7. Security Considerations Surprising defaults and/or undocumented behaviors are not good for security. This document attempts 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 +9. Acknowledgments The authors thank Martijn Schmidt, Qin Wu for the Huawei data point, - Job Snijders, David Farmer,John Heasley, and Jakob Heitz. + Greg Hankins, Job Snijders, David Farmer, John Heasley, and Jakob + Heitz. 10. Normative References [IANA-WKS] - "IANA Well-Known Comunities", + "IANA Well-Known Communities", . [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,