Remoteas

Remote as, short for remote autonomous system, is a term used in Border Gateway Protocol (BGP) to refer to the autonomous system number (ASN) of a BGP neighbor. An autonomous system is a collection of IP networks under a single administrative domain that shares common routing policies. When two routers form a BGP session, each side identifies the other by its AS number. The remote AS is the ASN of the neighbor as configured on the local router.

In BGP, there are two main peering types that influence how remote-as is used. In external BGP (eBGP) sessions, the two peers belong to different ASes, so the remote AS is typically different from the local AS. In internal BGP (iBGP) sessions, the peers share the same AS, and the remote AS is usually the same as the local one. However, you still configure the remote-as value in many vendor configurations, primarily to declare the intended relationship and to enforce policy decisions.

Configuration typically involves a command that associates a neighbor IP with its remote AS. For example, in many vendor implementations: a neighbor statement specifying the neighbor's IP address is accompanied by remote-as followed by the neighbor’s AS number. The exact syntax varies by vendor, but the concept remains the same: remote-as identifies the AS on the other end of the BGP session.

Correct use of remote-as is important for proper route exchange, policy enforcement, and loop prevention. Misconfiguring the remote AS can prevent sessions from forming, cause routing anomalies, or expose routes to unintended paths. Remote-as remains a fundamental parameter in BGP peering and network interconnections.