Assigned BGP extended communities
draft-ietf-idr-reserved-extended-communities-01

Abstract

This document defines two IANA registries in order to assign transitive and non-transitive extended communities from. These are similar to the existing well-known BGP communities defined in RFC 1997 but provide an easier control of inter-AS community advertisement as a community could be chosen as transitive or non-transitive across ASes.

For that purpose, this document defines the use of the reserved AS number 0 for the transitive and non-transitive generic four-octet AS specific extended community types.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

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 http://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 November 24, 2011.

Copyright Notice

Copyright (c) 2011 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 (http://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.

1. Introduction

[RFC1997] defines the BGP community attribute and some BGP well-known communities whose meaning SHALL be understood by all compliant implementations. New communities can be registered in the IANA "BGP Well-known Communities" registry but it can't be assumed anymore that they will be known by all BGP implementations. Implementations or BGP policies which recognize them will behave as specified. Implementations which do not recognize those new reserved communities will propagate them from BGP neighbor to BGP neighbor and from AS to AS with an unlimited scope.

There is currently no agreed way to register a non transitive well-known community:

On one hand, [RFC1997] defines BGP Well-known communities with no structure to set their transitiveness across ASes. Without structure, communities can only be filtered by explicitly enumerating all community values that will be denied or allowed to BGP speakers in neighboring ASes. This is not satisfactory as this would require upgrading all border routers to understand this community before its first usage.

On the other hand, [RFC4360] defines the BGP extended community attribute with a structure including a type and a transitive bit "T". This transitive bit, when set, allows to restrict the scope of the community within an AS. But their is no IANA registry to allocate one well-known extended community. [RFC4360] defines IANA registries to allocate BGP Extended Communities types. Each type is able to encode 2^48 or 2^56 values depending on the type being extended or regular. Therefore, one needing to reserve a single non-transitive extended community would need to reserve an extended subtype which represents 2^48 communities, while a single value is used. This would both waste the resources and disable the ability to define global policies on reserved communities, such as to accept them or to filter them out.

To address this limitation, this document defines two IANA registries in order to allow the registration of transitive and non-transitive extended communities. These are similar to the existing Well-known BGP communities defined in [RFC1997] but provides a control on inter-AS community advertisement as a community could be chosen as transitive or non-transitive across ASes.

2. Assigned extended communities

[I-D.ietf-idr-as4octet-extcomm-generic-subtype] defines a generic sub-type for the four-octet AS specific extended community. The value of the four-octets Global Administrator sub-field contains a four-octet Autonomous System number. The value of their two-octet Local Administrator sub-field has semantics defined by the Autonomous System set in the Global Administrator sub-field.

This document updates [I-D.ietf-idr-as4octet-extcomm-generic-subtype] and defines the use of the Local Administrator sub-field when the AS number encoded in the Global Administrator sub-field has the reserved value 0.

When the AS number encoded in the Global Administrator sub-field has the reserved value 0, the communities have global significance. The lists of those communities are maintained by the IANA in the registries "Assigned transitive extended communities" for the "transitive generic four-octet AS specific" extended community type and "Assigned non-transitive extended communities" for the "non-transitive generic four-octet AS specific" extended community type.

Note that this use of the reserved AS number 0 in the AS field of the communities is similar to the one defined by [RFC1997] for the BGP Well-Known communities.

3. IANA Considerations

The IANA is requested to create and maintain a registry entitled "Assigned transitive extended communities" with the following registration procedure:

 Registry Name: Assigned transitive extended communities

    Range              Registration Procedures
    -----------        -------------------------
    0x0000-8000        First Come First Served
    0x8001-FFFF        Standards Action/Early IANA Allocation

The IANA is requested to create and maintain a registry entitled "Assigned non-transitive extended communities" with the following registration procedure:

 Registry Name: Assigned non-transitive extended communities

    Range              Registration Procedures
    -----------        -------------------------
    0x0000-8000        First Come First Served
    0x8001-FFFF        Standards Action/Early IANA Allocation

An application may need both a transitive and a non-transitive community and it may be beneficial to have the same value for both communities. (Note that both extended communities will still be different as they will differ from their T bit). The IANA SHOULD try to accommodate such request to get both a transitive and non-transitive assigned community with the same value for both.

4. Security Considerations

This document defines IANA actions. In itself, it has no impact on the security of the BGP protocol.

5. References

Authors' Addresses

Table of Contents

• 1. Introduction
• 2. Assigned extended communities
• 3. IANA Considerations
• 4. Security Considerations
• 5. References
• Authors' Addresses