Information Technology Reference
In-Depth Information
Study Guide
Link-State Routing
Distance vector routing protocols are like road signs because routers must make preferred path decisions
based on a distance or metric to a network. Just as travelers trust a road sign to accurately state the
distance to the next town, a distance vector router trusts that another router is advertising the true distance
to the destination network.
Link-state routing protocols take a different approach. Link-state routing protocols are more like a
road map because they create a topological map of the network, and each router uses this map to
determine the shortest path to each network. Just as you refer to a map to find the route to another
town, link-state routers use a map to determine the preferred path to reach another destination.
Link-State Routing Concepts Exercise
Link-State Routing Protocols
Link-state routing protocols are also known as
shortest path first
protocols and are built around Edsger
Dijkstra
's SPF algorithm.
The IP link-state routing protocols include
Open Shortest Path First
(
OSPF
)
■
Intermediate System
-
to
-
Intermediate System
(
IS
-
IS
)
■
Introduction to the SPF Algorithm
The SPF algorithm accumulates
costs
along each path, from source to destination. Each router calculates
the SPF algorithm and determines the
cost
from its own perspective. Using Figure 10-1, complete
Table 10-1 through 10-5, filling in the appropriate information for each router. As an example, Table 10-1
for R1 is partially complete.
