The intra-routing algorithm of the AS (Autonomous systems) is used to describe the least-cost path from each router (internal router) to the gateway.
It is not necessary that every autonomous system should use the same Intra-autonomous system routing algorithm because each Autonomous systems (AS) has an administrative control for routing within AS.
Within the autonomous systems, all the routers are used a same intra-autonomous routing protocol, but the autonomous routing protocol can connect the autonomous systems to the other autonomous systems. It means the ASs run the same inter-AS routing protocol among themselves.
Therefore, it is not necessary that every autonomous system use the same intra-AS routing algorithm.
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