8.6 BGP Attributes
8.6.15
The Origin attribute
The Origin attribute is a well-known mandatory attribute (type code 1) that indicates the origin of the routing update. BGP allows three types of origins:
  • IGP - The prefix is internal to the originating AS.
  • EGP - The prefix was learned via some EGP, such as BGP.
  • Incomplete - The prefix was learned by some other means, probably redistribution.

BGP considers the Origin attribute in its decision-making process to establish a preference ranking among multiple routes. Specifically, BGP prefers the path with the lowest origin type, where IGP is lower than EGP, and EGP is lower than INCOMPLETE.