What information can be used by a router running a link-state protocol to build and maintain its topological database? (Choose two.)
A. hello packets
B. SAP messages sent by other routers
C. LSAs from other routers
D. beacons received on point-to-point links
E. routing tables received from other link-state routers
F. TTL packets from designated routers
Link state protocols, sometimes called shortest path first or distributed database protocols, are built around a well-known algorithm from graph theory, E. W. Dijkstra’a shortest path algorithm. Examples of link state routing protocols are:
Open Shortest Path First (OSPF) for IP
The ISO’s Intermediate System to Intermediate System (IS-IS) for CLNS and IP
DEC’s DNA Phase V
Novell’s NetWare Link Services Protocol (NLSP)
Although link state protocols are rightly considered more complex than distance vector protocols, the basic functionality is not complex at all:
1. Each router establishes a relationship—an adjacency—with each of its neighbors.
2. Each router sends link state advertisements (LSAs), some
3. Each router stores a copy of all the LSAs it has seen in a database. If all works well, the databases in all routers should be identical.
4. The completed topological database, also called the link state database, describes a graph of the internetwork. Using the Dijkstra algorithm, each router calculates the shortest path to each network and enters this information into the route table.
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