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 –
The “i” at the end of the first routing entry indicates the 18.104.22.168/24 network was originated via an IGP, via the BGP network command. The 22.214.171.124/24 network was redistributed into BGP in AS 3, since it shows “?” at the end of that routing entry