A router topology is a graph with exact integer link weights. This lesson pins the graph that the rest of the book uses.
Why weights matter
A routing topology becomes a shortest-path problem when every link has a small integer weight.
The pinned graph
This anchor graph has 6 routers and 9 undirected weighted links.
Read one link both ways
The A-C link has weight 2. Because the topology is undirected, that same cost applies from C back to A.
Start near A
From A, C has weight 2 while B has weight 4.
Use cost, not hop count
The path through C then D costs 2 plus 3, so D can be reached at 5 before the direct-looking B-D link with weight 10.
Summary
The graph is small and exact: routers are labels, links are undirected edges, and every displayed weight is an integer checked by the model.
weighted topology