BGP cannot discover routes and needs to import routes such as IGP routes into BGP routing tables so that the imported routes can be transmitted within an AS or between ASs. BGP imports routes in either redistribute or network mode:
In redistribute mode, BGP redistributes IGP routes, including RIP, OSPF, and IS-IS routes, into BGP routing tables based on protocol type. To ensure the validity of imported IGP routes, BGP can also import static routes and direct routes in redistribute mode.
In network mode, BGP imports the routes in the IP routing table one by one to BGP routing tables. The network mode is more accurate than the import mode.
- In Redistribute Mode