BGP ORIGIN ATTRIBUTE

The Origin attribute identifies the originating source of the route –

  • i (IGP) – Originated from an interior gateway protocol (such as EIGRP,RIP etc).This indicates the route was injected into BGP via the network command under the BGP process.
  • e (EGP) – Originated from an external gateway protocol.
  • ? (incomplete) – Unknown origin. This usually indicates the route was redistributed into BGP (from either connected, static, or IGP routes). An origin code of “?” is the least preferred.
  • From amongst the above 3 origin codes, “i”is the most preferred while “?” is the least preferred.

Below is the scenario where 3 Routers R1, R2 and R3 are connected in serial. With each in different Autonomous system no i.e. 1, 2 and 3 respectively.


In the BGP routing table of R2 , the origin code is listed at the end of each line in the table –

bgp-origin-attribute

The “i” at the end of the first routing entry indicates the 1.1.1.0/24 network was originated via an IGP, via the BGP network command. The 3.3.3.0/24 network was redistributed into BGP in AS 3, since it shows “?” at the end of that routing entry

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