Page 147 - Handout Computer Network.

Computer Network 2026

6.7.2.2 How Link-State Protocols Exchange Routing Information

Link-state network-discovery mechanisms are used to create a common picture of the
entire network. All link-state routers share this view of the network. This is similar to having
several identical maps of a town. In Figure 6-18, four networks (W, X, Y, and Z) are connected by
three link-state routers.
Network discovery for link-state routing uses the following processes:

1. Router’s exchange LSAs with each other. Each router begins with directly
connected networks for which it has direct, firsthand information.

2. Each router, in parallel with the others, constructs a topological database
consisting of all the LSAs from the internetwork.
3. The SPF algorithm computes network reachability. The router constructs this
logical topology as a tree, with itself as root, consisting of all possible paths to each network in
the link state protocol internetwork. It then sorts these paths by shortest path first (SPF).
4. The router lists its best paths and the ports to these destination networks in the
routing table. It also maintains other databases of topology elements and status details.

Figure 6-18 shown a Link-State SPF Calculations

When a router becomes aware of a link-state topology change, it forwards the
information so that all other routers can use it for updates. This involves sending common
routing information to all routers in the internetwork.
To achieve convergence, each router keeps track of its neighbor routers, the router
name, interface status, and the cost of the link to the neighbor. The router constructs an LSA

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