Information Technology Reference
In-Depth Information
Figure 4-1
Network Discovery: Cold Start (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
172.19.0.0
S0/0/1
0
Initial Exchange of Routing Information
What is required before the routers will start sending each other updates?
A routing protocol must be configured on each router.
For the first round of updates after a cold start, what information will the updates include?
The first round of updates only includes information about each router's directly connected networks.
In Figure 4-2, the routers have completed their initial exchange of routing 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 4-2
Network Discovery: Initial Exchange (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
S0/0/1
1
At this point in the network discovery process, the routing tables are incomplete. In other words, the
network has not yet converged.
Which routing tables and which networks still need to be discovered?
R1 does not yet know about 172.20.0.0.
R3 does not yet know about 172.16.0.0.
