9.6 BGP Attributes  
  9.6.14 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 the following three types of origins:
  • IGP – The prefix is internal to the originating AS.
  • EGP – The prefix was learned by way of 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.

 

Web Links

Configuring BGP

http://www.cisco.com/univercd/cc/td/doc/product/ software/ios122/122cgcr/fipr_c/ipcprt2/1cfbgp.htm