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
Explanation:
http://www.ciscopress.com/articles/article.asp?p=24090&seqNum=4
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.
OSPF Tutorial
http://www.9tut.com/ospf-routing-protocol-tutorial
Neighbor discovery is the first step in getting a link state environment up and running. In keeping
with the friendly neighbor terminology, a Hello protocol is used for this step. The protocol will
define a Hello packet format and a procedure for exchanging the packets and processing the
information the packets contain.
After the adjacencies are established, the routers may begin sending out LSAs. As the term
flooding implies, the advertisements are sent to every neighbor. In turn, each received LSA (Link state advertisement) is
copied and forwarded to every neighbor except the one that sent the LSA.
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