Information Technology Reference
In-Depth Information
Next Update
Continuing the journey toward convergence, the routers exchange the next round of periodic updates.
In Figure 4-3, the routers have completed their next round of updates. In the tables below each router,
fill in the networks, interfaces, and hop counts that each router now has installed in its routing table.
Figure 4-3
Network Discovery: Next Update (Answer)
172.18.0.0
Fa0/0
172.16.0.0
172.17.0.0
172.19.0.0
172.20.0.0
Fa0/0
Fa0/0
S0/0/0
S0/0/1
S0/0/0
S0/0/1
R1
R2
R3
Network
Interface
Hop
Network
Interface
Hop
Network
Interface
Hop
172.16.0.0
172.17.0.0
Fa0/0
0
0
172.17.0.0
172.18.0.0
S0/0/0
0
0
172.19.0.0
172.20.0.0
S0/0/1
0
0
S0/0/0
Fa0/0
Fa0/0
172.18.0.0
S0/0/0
1
172.19.0.0
S0/0/1
0
172.18.0.0
S0/0/1
1
172.19.0.0
S0/0/0
1
172.16.0.0
S0/0/0
1
172.17.0.0
S0/0/1
1
172.20.0.0
S0/0/0
2
172.20.0.0
S0/0/1
1
172.16.0.0
S0/0/1
2
Routing Table Maintenance
After the routers have initially learned about remote networks, routing protocols must maintain the
routing tables so that they have the most current routing information. How the routing protocol main-
tains the routing table depends on the type of routing protocol (distance vector, link-state, or path vec-
tor) as well as the routing protocol itself (RIP, EIGRP, and so on). The exercise in the following sec-
tion will reinforce your knowledge of routing table maintenance.
Distance Vector Table Maintenance Techniques Exercise
Periodic Updates
Explain the term
periodic update
.
The term periodic update refers to the fact that a router sends the complete routing table to its neigh-
bors at a predefined interval, regardless of whether there has been a topology change.
The age of routing information in a routing table is refreshed each time an update is received. This
way, information in the routing table can be maintained when there is a topology change.
List four ways that changes in the topology might occur.
Failure of a link
■
Introduction of a new link
■
Failure of a router
■
Change of link parameters
■
RIP Timers
In addition to the update timer, the IOS implements three additional timers for RIP. Briefly explain
what these timers are and how they are used.
