Three methods can be used to originate a prefix in BGP
1. Configuring the BGP "Network" command
2. Redistribution from routing sources other than EGP
3. Redistribution from EGP (the inter-domain routing protocol Exterior Gateway Protocol)
Three Methods of originating BGP updates correspond with the three and only three origin code types set by BGP. the origin code is mandatory transitive BGP attribute. A brief description of each origin code is provided below:
> "i" ORIGIN is IGP; this shows that the prefix was originated via network statement.
> "?" ORIGIN is incomplete, this shows that the prefix was originated via redistribution.
> "e" ORIGIN is EGP, this shows that the prefix was originated from an EGP routing process.