Practical BGP

BGP Attributes

BGP attributes are a confusing array of information carried in a BGP update capable of indicating anything from path preference to various additional pieces of information about a route, either within an autonomous system or outside an autonomous system. There are four basic types of attributes:

• Well-known mandatory attributes; these attributes must be recognized by all BGP speakers and must be included in all update messages. Almost all of the attributes impacting the path decision process, described in the next section, are well-known mandatory attributes.

• Well-known discretionary attributes; these attributes must be recognized by all BGP speakers and may be carried in updates but are not required in every update.

• Optional transitive ...