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| 9.1 |  | Autonomous Systems |
| 9.1.4 |  | Multihomed transit autonomous systems |

A multihomed transit system has more than one connection to the outside world and can be used for transit traffic by other autonomous systems. The multihomed AS views transit traffic as any traffic originating from outside sources bound for outside destinations.

A transit AS can route transit traffic by running BGP internally so that multiple border routers in the same AS can share BGP information. Additional routers may be used to forward BGP information from one border router to another. BGP can be run inside an AS to facilitate this exchange.

When BGP is running inside an AS, it is referred to as Internal BGP (IBGP). When BGP runs between autonomous systems, it is called External BGP (EBGP). If the role of a BGP router is to route IBGP traffic, it is called a transit router. Routers that sit on the boundary of an AS and that use EBGP to exchange information with the ISP are called border or edge routers.