Information Technology Reference
In-Depth Information
Reliability is measured by the expected, received keepalives of a link. If the ratio is high, the
line is reliable. The best rating is 255/255, which is 100 percent reliability. Example 2-3 shows
that the reliability of an interface can be verified using the show interface command.
show interface Command to Check the Reliability of an Interface
Example 2-3
router4#show interface serial 0
Serial0 is up, line protocol is up
Hardware is PQUICC Serial
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
rely 255/255
Loop Prevention Schemes
Some routing protocols employ schemes to prevent the creation of routing loops in the network.
These schemes are the following:
Simple split horizon
Split horizon with poison reverse
Counting to infinity
These schemes are discussed in the following sections.
Simple Split Horizon
Distance vector routing protocols use the split horizon technique to prevent routing loops.
Routes that are learned from a neighboring router are not sent back to that neighboring router,
thus suppressing the route. If the neighbor is already closer to the destination, it already has a
better path.
In Figure 2-9, Routers 1, 2, and 3 learn about Networks A, B, C, and D. Router 2 learns about
A from Router 1 and also has Network B and C in its routing table. Router 3 advertises Network
D to Router 2. Now, Router 2 knows about all the networks. Router 2 sends its routing table to
Router 3 without the route for Network D because it learned that route from Router 3.
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