Is it necessary for EIGRP AS numbers to match between neighbors?

For Enhanced Interior Gateway Routing Protocol (EIGRP), it is essential that the Autonomous System (AS) numbers match between neighboring routers for them to establish a successful neighbor relationship. When two routers form an EIGRP adjacency, they exchange routing information and updates. This process begins with an EIGRP Hello packet, which includes various parameters, with the AS number being one of the most critical. If the AS numbers do not match, the routers will not recognize each other as neighbors and will not exchange routing information, leading to routing inconsistencies and connectivity issues.

In essence, for EIGRP to operate correctly within a network, all routers that participate in the same EIGRP routing domain must share the same AS number. This design choice helps maintain stability and consistency in the routing environment.