BGP Community Container Attribute

RFC 1997 defines the BGP Community Attribute. This attribute is used as a tool to carry additional information in BGP routes which may help to automate peering administration. The BGP Communities Attribute consists of a set of one or more four-octet values, where each specifies a different community. Except for two reserved ranges, the encoding of community values mandates that the first two octets are to contain the Autonomous System number, with the next two octets containing some locally defined value. Since the introduction of , numerous additional mechanisms have been introduced to provide BGP Community-like functionality. Each of these mechanisms introduce a new syntax, typically covered by its encoding with the BGP Path Attribute that defines it, and a semantic space. The authors believe that defining a new BGP Path Attribute, with the ability to contain locally defined parameters will enhance the current level of network policies, as well as simplify BGP policy management. The proposed encoding will also facilitate the delivery of new network services without a need to define a new BGP extension each time. When defining any new type of tool there is always a unique opportunity to specify a subset of well recognized behaviors. Lists of the current most commonly used BGP communities, as well as provision for a new registry for future definitions will be contained in a separate document.

This specification defines a new BGP Path Attribute, the BGP Community Container. It carries a series of BGP Community Container types, each prefaced with the BGP Community Container Common Header. This specification also defines the BGP Wide Community Container.

The BGP Community Container Common Header permits Community-like attributes to be grouped under a single BGP Path Attribute. This provides hierarchy for future Community-like features. It permits implementations without knowledge of a specific Community Container's format to address that Community Container by its code point. It also permits common enforcement of the Community Container's transitivity across AS boundaries without need for the implementation to understand a specific Container's implementation. The BGP Community Container Common Header is defined in and contains following encoding: Container Type 1, BGP Wide Community is defined in this document. Flags control common behavior including the transitivity of the Container. Length of the Container contents.

This document defines one Community Container with the following encoding:

The container type 1 "BGP Wide Community TLVs" is defined in . This section defines the action that an operator wishes a router to take. This is the AS originating the community. AS that defines and provides the semantics to interpret this Community. This is an optional list that encodes where the community's action should be taken. This is an optional list that encodes where the community's actions should not be taken. This is an optional list of Atoms that encodes additional information that the community's action needs to execute properly.

Atoms provide data types that can be used to encode contents of BGP Community Containers. They are in the format of TLVs and are defined later in this document in .

This document defines a new BGP Path Attribute, the BGP Community Container. The attribute type code is TBD. The BGP Community Container attribute is an optional, transitive BGP attribute, and may be present only once in the BGP UPDATE message. The attribute contains a set of typed containers. Any given container type may appear multiple times, unless that container type's definition specifies otherwise.

Containers always start with the following common header: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Flags |C|T| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This document defines container type 1. See the for information on additional type registration policies. Bit Value Meaning T0Not Transitive across administrative boundary. 1Transitive across AS and administrative boundary. C0Not transitive across confederation boundaries. 1Transitive across confederation boundaries. 3..7- RESERVED - MUST be zero when originated and SHOULD be ignored upon receipt. Flags are defined globally and apply to all container types. Bit 0 (T bit) Transitivity bit: When not set (value 0), the community in the container is transitive across AS boundaries, but not across an administrative boundary. When set (value 1), the community in the container is transitive across all ASes. An administrative boundary, in this sense, is an arbitrary set of connected ASes, possibly under control of a single entity. How such an administrative boundary is determined is out of scope of this document. Bit 1 (C bit) Confederation bit: The confederation bit is used to manage the propagation scope of a given BGP Wide Community across confederation boundaries. When not set (value 0) community is not transitive across confederation sub-AS boundary. When set (value of 1) indicates that community in a given container is transitive across confederation boundary. The Reserved field MUST be set to zero when originated and SHOULD be ignored upon receipt. The Length field represents the total length of a given container's contents in octets.

The Type 1 BGP Community Container, the BGP Wide Community, is of variable size (but minimum length 12). It is composed of a fixed 12-octets - containing the Community Value, the Source AS Number, and the Context AS Number - followed by optional TLVs: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |I| Community Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Context AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | TLVs (optional) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Community Value: 4 octets The Community Value indicates what set of actions a router is requested to take upon reception of a route containing this community. The semantics of this value depend on whether this is a private/local community or IANA registered. When the high order bit of the Community Value field - I - is set, the value is IANA Registered and has a well defined meaning with underlying semantics. See the documentation for each Registered BGP Wide Community for its semantics and validation requirements. When the high order bit of the Community Value field is clear, the value is Locally defined and has semantics solely within the control of the AS defining that community. The Context AS Number provides the namespace in which this Community Value is interpreted. It is that AS's responsibility to provide the semantics and validation requirements for that BGP Wide Community. See for code point space partitioning.

Source Autonomous System Number: 4 octets The Autonomous System number indicates the AS originating this BGP Wide Community.

Context Autonomous System Number: 4 octets This identifies the AS that provides the semantics to interpret this Community.

Optional type 1 container TLVs are encoded in the following format:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+ | Sub-Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The sub-type of the BGP Wide Community TLV. A given Sub-Type MUST NOT appear more than once. Length of the "Value" field in octets. Specific to the underlying Sub-Type.

The value field of the Wide Community Target(s) TLV (Sub-Type 1) is a series of Atom TLVs. The semantics of any given Atom TLV MUST be part of the definition of a given Wide Community. BGP Wide Community Targets define the matching criteria for the community. A given wide community may have a number of targets that it applies to. The semantics of these targets will vary on a per community basis. Depending on the definition of the community, targets may be optional. Wide Community Targets consist of a series of Atoms that have "match any" semantics. Thus, if any given target matches per the semantics of that Atom for the community, the community is considered to match and the action defined by the community should be executed. When no Target(s) TLV is specified, it is considered "match all". If the semantics of a given Atom is undefined for the community in question, this Atom MUST be ignored. When no targets are required by the definition of a given Wide Community, the Wide Community Target(s) TLV SHOULD NOT be encoded in the community. Implementations MUST be prepared to accept a Wide Community Target(s) TLV with an empty value field.

The BGP Wide Community Exclude Target(s) TLV (Sub-Type 2) contains a list of a Atoms. Wide Community Exclude Targets define criteria by which the community is considered to NOT match. Depending on the semantics of the BGP Wide Community, Exclude Target(s) may be optional. The semantic of the BGP Wide Community Exclude Target(s) is to match all specified Target(s) with the exception of those listed in this TLV. The value field of the BGP Wide Community Exclude Target(s) TLV is a series of BGP Wide Community Atom TLVs. The semantics of any given Atom TLV MUST be part of the definition of a given Wide Community. If the semantics of a given Atom is undefined for the community in question, this Atom MUST be ignored. If the BGP Wide Community Target(s) TLV and the BGP Wide Community Exclude Target(s) TLV have conflicting semantics, priority MUST be given to the Wide Community Exclude Target(s) TLV. When no exclude targets are required by the definition of a given BGP Wide Community, the BGP Wide Community Exclude Target(s) TLV SHOULD NOT be encoded in the community. Implementations MUST be prepared to accept a BGP Wide Community Exclude Target(s) TLV with an empty value field.

The BGP Wide Community Parameter(s) TLV (Sub-Type 3) contains a list of a Atoms. A given BGP Wide Community may have parameters that are used as inputs for executing actions defined for that community. These parameters, and any constraints implied by the parameters, MUST be defined by the wide community definition. Parameters consist of an ordered set of Atom sub-TLVs. The semantics of any specific positional instance of an Atom MUST be defined by the wide community. Care must be taken when using Atoms with list semantics. If the desired behavior is a single or limited number of instances of that type, this should be documented as part of the use case of that BGP Wide Community. If it is the case that a parameter for a given community is of an unexpected type or length, the BGP Wide Community MUST be ignored. If it is the case that there are too many or two few parameters for a given community, the BGP Wide Community MUST be ignored. When no parameters are required by the definition of a given Wide Community, the Wide Community Parameters TLV SHOULD NOT be encoded in the community. Implementations MUST be prepared to accept a Wide Community Parameter TLV with an empty value field.

The detailed interpretation of the targets or parameters SHALL be provided when describing given community type in a separate document or when locally defined by an operator.

Some types of BGP Community Contaners, for example BGP Wide Communities, will act on and hence need to encode some distinct Atoms of data. Use of Atoms is solely subject to definition of the specific BGP Container type. Atoms are encoded as TLVs, where each TLV has the following format:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+ | Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type field contains a value of 1-254. The values 0 and 255 are reserved for future use. The TLV types are to be assigned and maintained by IANA registry; see . The Length represents the length of the "Value" field in octets. The Value field contains the TLV value. Supported format of the TLVs can be:

Type 1: Autonomous System Number List. Type 2: IPv4 Prefix (1 octet prefix length + prefix) List. Type 3: IPv6 Prefix (1 octet prefix length + prefix) List. Type 4: Integer32 List. Type 5: IEEE Floating Point Number List. Type 6: Neighbor Class List. Type 7: User-defined Class List. Type 8: UTF-8 String. The semantics of a given Atom will depend upon the context in which it is used, as defined by the containing wide community. In the following sections defining the different Atoms, validation rules for the Length of the Atom will be presented. If the Length of the Atom does not match the rules for that Atom, it SHALL be considered malformed. (See .) In general, Atoms of List type have the semantics of sets. Duplicate entries SHOULD NOT be present and MAY be removed by BGP Speaker propagating the Lists. The presence of duplicate entries have no additional semantics.

This Atom represents a list of Autonomous System numbers, each 4 octets in size. When encoding two octet ASes, the first two octets of this four octet value MUST be filled with zeros. The minimum Length of this Atom is 4 octets. The Length MUST be a multiple of 4. Two special values are reserved for the Autonomous System Atoms:

0x00000000 - to indicate "No Autonomous Systems". 0xFFFFFFFF - to indicate "All Autonomous Systems".

This Atom represents a list of IPv4 or IPv6 prefixes. IPv4 and IPv6 Prefix Atom values are encoded in the same format used by BGP NLRI in Section 4.3 of .

+---------------------------+ | Prefix Length (1 octet) | +---------------------------+ | Prefix (variable) | +---------------------------+ The Prefix Length for IPv4 prefixes MUST be in the range of 0..32. The Prefix Length for IPv6 prefixes MUST be in the range of 0..128. The Length field must be able to accommodate the list of prefixes according to the encoding rules. If the Length cannot fully accommodate the required number of octets to encode the Prefix Length and the Prefix, the Atom is considered malformed.

This Atom represents a list of four-octet Integers. These Integers are stored in network byte order. The minimum Length of the Integer32 list Atom is 4 octets. The Length MUST be a multiple of 4.

This Atom represents a list of floating point numbers. Floating point numbers are a fixed Length of 4 octets and are stored in format. The minimum Length of the Floating Point Number list Atom is 4 octets. The Length MUST be a multiple of 4.

The Neighbor Class list Atom represents a list of Neighbor classes, each 4 octets in size. Neighbor class currently can contain three values: This class is typically applied to sessions where a transit-free relationship exists between two providers. This class is typically applied to sessions where the remote end of the session is operated by a customer. This class is typically applied to sessions where the remote end of the session is operated by a network from which you receive transit routes. The minimum Length of the Neighbor Class list Atom is 4 octets. The Length MUST be a multiple of 4.

The User-defined Class list Atom represents a list of user-defined class, each 4 octets in size. The exact property definition is up to the semantics of the defining Autonomous System. The semantics governing a given User-defined Class list are defined by the Context AS Number and the Community Value. Examples of User-defined Class properties include geography (East, West), continent (North America, Asia, Europe), etc. Similar to the BGP Communities, it is necessary that the Context AS provide a registry of the value and the semantics of a given community. The minimum Length of the User-defined Class list Atom is 4 octets. The Length of this Atom MUST be a multiple of 4.

The UTF-8 String Atom represents an arbitrary Unicode string in UTF-8 format. The Length is required to be of sufficient size to carry the UTF-8 string in the Value field. Implementations MUST be prepared for truncated/improperly formed UTF-8 strings. When detecting such a string, the implementation should remove trailing octets of a multi-octet sequence in order to have a well-formed string. Implementations MUST be prepared to receive empty (zero-Length) UTF-8 String Atoms as they may be used as Parameters.

According to RFC 1997, as well as IANA's Well-Known BGP Communities registry, the following BGP communities are defined to have global significance:

0xFFFF0000 planned-shut [draft-francois-bgp-gshut] 0xFFFFFF01 NO_EXPORT [RFC1997] 0xFFFFFF02 NO_ADVERTISE [RFC1997] 0xFFFFFF03 NO_EXPORT_SUBCONFED [RFC1997] 0xFFFFFF04 NOPEER [RFC3765] This document recommends for simplicity as well as for avoidance of backward compatibility issues the continued use of BGP Standard Community Path Attribute, type 8, as defined in RFC 1997 to distribute non-Autonomous System specific Well-Known BGP Communities. For the same reason, this document does not intend to obsolete the currently defined and deployed BGP Extended Communities.

Having multiple ways to propagate locally assigned BGP Communities - via the use of Standard, Extended or Large BGP Communities versus the use of BGP Wide Communities - may seem to potentially cause problems when considering propagation of conflicting actions. However, even at present, an operator may append such Communities with conflicting information. It is therefore recommended that any implementation, in supporting both standard and BGP Wide Communities, allow for their easy inbound and outbound processing. The actual execution of all communities should be treated as a union and, if supported by an implementation, their execution permissions are to be a local configuration matter.

"treat as withdraw" behavior is expected for any malformed Community Containers or malformation of their contents. Each Community Container type may have additional validation rules, including permitted length of Atoms. Failure to conform to those additional rules MUST also be treated as a malformed Community Container.

If any Atom in a BGP Wide Community container's Exclude Targets TLV is unrecognized, that Wide Community MUST NOT be considered a match and no actions for that community should be processed. While the Targets TLV is meant to be inclusive, the Exclude Targets TLV is meant to be proscriptive of applying the action.

An operator of an AS 64496, wishes to locally define a Wide Community with the semantics of permitting AS_PATH prepending with targets that include AS numbers of peer ASes and peers who have been marked with a set of enumerated city locations. AS 64496 has selected Community Value 1 to represent this functionality. AS 64496 has established a registered set of values to use for its User-defined Class: 100 - Amsterdam 101 - New York 102 - San Francisco 103 - Tokyo 104 - Moscow Target semantics: The Autonomous System Number list Atom refers to the target peer AS Numbers. The User-defined Class for AS 64496 has been defined elsewhere and the values 100..104 may be used for this locally defined Wide Community. The Targets TLV MUST contain at least one entry. The Exclude Targets TLV MAY contain entries of the above supported Atoms. The semantics of all other Atoms are undefined for this community. Parameter semantics: The parameter TLV shall consist of exactly one Integer32 Atom value that is constrained to have a value of 2..8.

AS_PATH prepend 4 TIMES TO AS 2424, AS 8888, to peers marked as Amsterdam (100) or to peers marked Moscow (104), but not to peers in New York (101). The T Flag (transitive) is set to prevent propagation of this community.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type (1, Wide) | Flags |0|1| Reserved(0) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length: 53 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Community: LOCAL PREPEND ACTION CATEGORY 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source AS 64496 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Context AS 64496 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Target TLV (1)| Length: 18 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ASN List (1) | Length: 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Target ASN# 2424 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Target ASN# 8888 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | User List(7) | Length: 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Amsterdam (100) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Moscow (104) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |ExcTargetTLV(2)| Length: 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | User List(7) | Length: 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | New York (101) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Param TLV (3) | Length: 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Integer32 (4) | Length: 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prepend # 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Transitive BGP Community Container communities could unintentionally spread far from their origin. If a router receives many routes from multiple sources on the Internet with different communities, it could cause significant memory usage. To prevent excessive memory usage, routers should be configured to strip unexpected communities from received routes. All the security considerations for BGP Communities or BGP Extended Communities apply to BGP Community Containers.

For BGP Wide Communities, the Community Value the Source AS may provide sufficient context to strip unwanted or unexpected communities. Given the flexibility and power offered by BGP Wide communities, it is important to consider the additional possibilities allowed by their definition. In particular, for locally defined BGP Wide Communities, it may be wise to restrict the range of parameters. For registered BGP Wide Communities, the security considerations of the document defining them MUST address issues specific to those newly defined Communities.

This document defines a new BGP Path Attribute called BGP Community Container Attribute. For this new type IANA is requested to allocate a new value in the corresponding registry: Registry Name: BGP Path Attributes This document makes the following assignments for the optional, transitive BGP Community Container Attribute:

Name Type Value ---- ---------- BGP Community Container Attribute TBD

This document requests IANA to define and maintain a new registry named: "BGP Community Container Atom Types". The pool of 0x00-0xFF has been defined for its allocations.

Registration procedures: 0x00: Reserved. 0x01-0x08: Defined in this document. 0x09-0xFE: IETF Consensus. 0xFF: Reserved.

This document makes the following assignments for the BGP Community Container Atom Type values registry: Name Type Value ---- ---------- Autonomous System Number List 0x01 IPv4 Prefix list 0x02 IPv6 Prefix list 0x03 Integer32 list 0x04 IEEE Floating Point Number list 0x05 Neighbor Class list 0x06 User-defined Class list 0x07 UTF-8 string 0x08

This document requests IANA to define and maintain a new registry named: "BGP Community Container Neighbor Class List Atom Types". The pool of 0x00000000-0xFFFFFFFF has been defined for its allocations.

Registration procedures: 0x00000000 : Reserved. 0x00000001-0x00000003 : Defined in this document. 0x00000004-0xFFFFFFFE : IETF Consensus. 0xFFFFFFFF : Reserved.

This document makes the following assignments for the BGP Community Container Neighbor Class List Atom Types registry: Name Type Value ---- ---------- Peer 1 Customer 2 Upstream 3

This document requests IANA to define and maintain a new registry named: "BGP Community Container Types". The pool of: 0x0000..0xFFFF has been defined for its allocations.

Registration procedures: 0x0000 : Reserved. 0x0001 : BGP Wide Community (defined in this document). 0x0002-0x0004 : Reserved. 0x0005-0x00FF : IETF Consensus. 0x0100-0xFF00 : First Come, First Served. 0xFF01-0xFFFE : Experimental. 0xFFFF : Reserved.

This document requests IANA to define and maintain a new registry named: "Registered Type 1 BGP Wide Community Community Types". The pool of 0x00000000..0xFFFFFFFF has been defined for its allocation.

Registration procedures: 0x00000000 : Reserved. 0x00000001-0x7FFFFFFF : Available for private/local use. 0x80000000 : Reserved. 0x80000001-0xFFFFFEFF : First Come, First Served for registered use. 0xFFFFFF00-0xFFFFFFFE : Experimental. 0xFFFFFFFF : Reserved.

This document requests IANA to define and maintain a new registry named: "Registered Type 1 BGP Wide Community Optional Sub-Types". The pool of 0x00..0xFF has been defined for its allocation.

Registration procedures: 0 : Reserved. 1..3 : Defined in this document. 4..254 : IETF Consensus. 255 : Reserved.

This document makes the following assignments for the Registered Type 1 BGP Wide Community Optional Sub-Types registry: Name Type Value ---- ---------- Targets 1 Exclude Targets 2 Parameters 3

Changes from -03 to -04: Many editorial changes. Restored the structure of the common header to accommodate prior implementations from Huawei. However, do not keep the Hop count per prior IDR and author discussion. Adopt the name BGP Community Container for the general feature and common header after discussion on IDR regarding Large BGP Communities. Wide communities now specifically refer to the Type 1 container. Updated the Common Container Header's definition of Length to only cover the length of the contents, and not the header. Hide the Type 2 (4:4), Type 3 (Nx4), Type 4 (16+Nx4) containers for now. Outstanding issues addresses and section removed. Type 1 container renamed from "Wide community" to "Wide community TLVs". Rename Integer Atom to Integer32. Example changed, following previous specification change. Changes from -02 to -03: Many editorial change. Introduction of new type of containers: Type 2 (4:4), Type 3 (Nx4), Type 4 (16+Nx4) Common container header: Type length changed from 2-octets to 1 octet, "Hop Count" removed, "Context AS number" moved from type 1 to the generic header. Remove community "AS-4 List Generic Wide BGP Community" Changes from -00 to -02: no change 00: no change

Changes from -03 via -04 to -05: Update the Introduction. Substantial re-work of Atom types removing proposed Group container and moving Atoms to be lists. Added the Exclude Targets TLV to the Wide Community container. Added a section on error handling. Updated the example. Changes from -02 to -03: Removed C and R named bit fields originally from -00. Rename Target AS field to Context AS. Make Integer Atom a fixed 4 octets in length. Add Neighbor Class Atom Rename TTL to Hop Count Changes from -01 to -02: The Type field has been expanded to 2 octets. The Length field has been moved to the common header. Changed format to use TLVs. Added Atom TLV to define well defined syntactic items. Added TLVs to distinguish targets from parameters. Various editorial changes to language.

The following people contributed significantly to the content of the document:

Shintaro Kojima OTEMACHI 1st. SQUARE EAST TOWER, 3F 1-5-1, Otemachi, Chiyoda-ku, Tokyo 100-0004 Japan Email: koji@mfeed.ad.jp

Juan Alcaide Cisco Systems Research Triangle Park, NC United States Email: jalcaide@cisco.com

Burjiz Pithawala Cisco Systems 170 West Tasman Dr San Jose, CA United States Email: bpithaw@cisco.com

Saku Ytti TDC Oy Mechelininkatu 1a 00094 TDC Finland Email: ytti@tdc.net

This document owes draft-lange-flexible-bgp-communities a debt for the inspiration of many features contained herein. The authors would like to thank Enke Chen, Pedro Marques, Alton Lo, Igor Gashinsky and Job Snijders for their valuable input.