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Topology

Distance-vector routing starts with a small weighted neighbor graph.

highlighted = computed this step

A hears from a neighbor

Distance-vector routing lets a router improve its table by listening to a neighbor's advertised distances.

routers=4\text{routers}=4
Distance-vector topologyThe distance-vector topology is validated as exact integer router links.Distance-vector topology - weighted undirected topology15241ABCD

The links are tiny and exact

This toy network has 4 routers and 5 undirected weighted links.

links=5\text{links}=5
Distance-vector topologyThe distance-vector topology is validated as exact integer router links.Distance-vector topology - weighted undirected topology15241ABCD

A can use B as a next hop

The A to B link cost is 1, so every route through B starts by paying that cost.

w(A,B)=1w(A,B)=1
Distance-vector topologyThe distance-vector topology is validated as exact integer router links.Distance-vector topology - weighted undirected topology15241ABCD

Summary

The update uses only the pinned topology and the neighbor vector; the lesson does not trust a hand-written route.

via B starts with 1\text{via B starts with }1
Distance-vector topologyThe distance-vector topology is validated as exact integer router links.Distance-vector topology - weighted undirected topology15241ABCD