I'm studying networking from the book 'A top down approach' from Kurose and Ross.

In the book it is stated that routers are generally considered Layer 3 devices (i.e. implementing the stack up to the network layer).

RIP, a intra AS routing algorithm, should be a network layer component and yet it uses UDP as a mechanism for messages exchange.
Is this a violation of the general rule of isolation?Or am I getting something wrong?

  • 1
    "RIP, a intra AS routing algorithm" No, it is not. It is called a routing protocol. Routing protocols do not route and are not routing algorithms. A router routes based on what is in its routing table, and one way to populate the routing table is with a routing protocol, but the routing protocol doesn't route.
    – Ron Maupin
    Commented Jun 27, 2018 at 14:55

1 Answer 1


Routers can be considered layer 3 devices because they provide their main function (routing) based on layer 3 information.

But a routing protocol, like RIP, is actually an application that the router uses to communicate with other routers. It uses IP/UDP as its transport. It could be considered to be at the application layer.

The usual caveats about theoretical models vs real-world implementations apply.

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