Editing Border Gateway Protocol (section)

==== BGP Extended Community Attribute ====
The BGP Extended Community Attribute was added in 2006,<ref>{{IETF RFC|4360}}</ref> in order to extend the range of such attributes and to provide a community attribute structuring by means of a type field. The extended format consists of one or two octets for the type field followed by seven or six octets for the respective community attribute content. The definition of this Extended Community Attribute is documented in RFC 4360. The IANA administers the registry for BGP Extended Communities Types.<ref>{{Cite web |title=Border Gateway Protocol (BGP) Extended Communities |url=https://www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml |access-date=2022-12-04 |website=www.iana.org}}</ref> The Extended Communities Attribute itself is a transitive optional BGP attribute. A bit in the type field within the attribute decides whether the encoded extended community is of a transitive or non-transitive nature. The IANA registry therefore provides different number ranges for the attribute types. Due to the extended attribute range, its usage can be manifold. RFC 4360 exemplarily defines the "Two-Octet AS Specific Extended Community", the "IPv4 Address Specific Extended Community", the "Opaque Extended Community", the "Route Target Community", and the "Route Origin Community". A number of BGP QoS drafts also use this Extended Community Attribute structure for inter-domain QoS signalling.<ref>[http://www.bgp-qos.org/forum/viewforum.php?f=6 IETF drafts on BGP signalled QoS] {{webarchive|url=https://web.archive.org/web/20090223214439/http://www.bgp-qos.org/forum/viewforum.php?f=6 |date=2009-02-23 }}, Thomas Knoll, 2008</ref>

With the introduction of 32-bit AS numbers, some issues were immediately obvious with the community attribute that only defines a 16-bit ASN field, which prevents the matching between this field and the real ASN value. Since RFC 7153, extended communities are compatible with 32-bit ASNs. RFC 8092 and RFC 8195 introduce a Large Community attribute of 12 bytes, divided in three field of 4 bytes each (AS:function:parameter).<ref>{{cite web |url=http://largebgpcommunities.net/ |title=Large BGP Communities |access-date=2021-11-27}}</ref>