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10.0.0.0/16 is subnetted, 1 subnets
C 10.1.0.0 is directly connected, FastEthernet0/0
R 172.30.0.0/16 [120/1] via 209.165.200.230, 00:00:24, Serial0/0/0
[120/1] via 209.165.200.234, 00:00:15, Serial0/0/1
209.165.200.0/30 is subnetted, 2 subnets
C 209.165.200.228 is directly connected, Serial0/0/0
C 209.165.200.232 is directly connected, Serial0/0/1
Both the R1 and R3 are advertising routes to the 172.30.0.0/16 network; therefore, there
are two entries for this network in the R2 routing table. The R2 routing table shows only
the major classful network address of 172.30.0.0. It does not show any of the subnets for
this network that are used on the LANs attached to R1 and R3. Because the routing metric
is the same for both entries, the router alternates the routes that are used when forwarding
packets that are destined for the 172.30.0.0/16 network.
Examine the routing table on the R1 router.
Step 5.
R1# show ip route
Output omitted
R 10.0.0.0/8 [120/1] via 209.165.200.229, 00:00:02, Serial0/0/0
172.30.0.0/24 is subnetted, 2 subnets
C 172.30.1.0 is directly connected, FastEthernet0/0
C 172.30.2.0 is directly connected, FastEthernet0/1
209.165.200.0/30 is subnetted, 2 subnets
C 209.165.200.228 is directly connected, Serial0/0/0
R 209.165.200.232 [120/1] via 209.165.200.229, 00:00:02, Serial0/0/0
Both R1 and R3 are configured with interfaces on a discontiguous network, 172.30.0.0.
The 172.30.0.0 subnets are physically and logically divided by at least one other classful
or major network—in this case, the two serial networks 209.165.200.228/30 and
209.165.200.232/30. Classful routing protocols like RIPv1 summarize networks at major
network boundaries. Both R1 and R3 will be summarizing 172.30.0.0 subnets to
172.30.0.0. Because the route to 172.30.0.0/16 is directly connected, and because R1 does
not have any specific routes for the 172.30.0.0 subnets on R3, packets destined for the R3
LANs will not be forwarded properly.
Examine the routing table on the R3 router.
Step 6.
R3# show ip route
Output omitted
R 10.0.0.0/8 [120/1] via 209.165.200.233, 00:00:19, Serial0/0/1
172.30.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.30.100.0/24 is directly connected, FastEthernet0/0
C 172.30.110.0/24 is directly connected, Loopback0
C 172.30.200.16/28 is directly connected, Loopback1
C 172.30.200.32/28 is directly connected, Loopback2
209.165.200.0/30 is subnetted, 2 subnets
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