Solving Classful addressing problem, using RIP (CNA-02-005)

CCNA Exploration 4.0, Semester 2, "Solving Classful addressing problem, using RIP" Packet Tracer 5.0 practice file (CNA-02-005).

• CNA-02-005.pkt, (Backup Link)
• CNA-02-005-wrong-sol.pkt, (Backup Link)
• CNA-02-005-final-sol.pkt, (Backup Link)

In this example, the IP addressing scheme is only allowed in the our current new "Classless" world. That's why any old "Classful" routing protocols will not work.

The problem is at the routing entries in R2's routing table. Two "10.0.0.0/8" entries will be there. This is a typical "Classful" world behavior: when advertising routing information to other "classful network address"'s router, all subnet routes will be summarized into one route, which is exactly the same as your own "classful network address".

In this case, the "classful network address" is exactly "10.0.0.0/8".  The peer router is R2 and is not within this classful network address.

That's why 50% of packets destined for either 10.1.1.0/24 or 10.2.2.0/24 would go to the wrong router and get dropped!

Here is the wrong routing table, by using RIP version 1 (CNA-02-005-wrong-sol.pkt, Backup Link):

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

R    10.0.0.0/8 [120/1] via 192.168.4.1, 00:00:17, Serial0/0/1
                [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
     172.30.0.0/24 is subnetted, 3 subnets
R       172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
R    192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:17, Serial0/0/1
R2>

Therefore, we can only implement "Classless" protocols, such as RIP version 2. (CNA-02-005-final-sol.pkt, Backup Link). Also remember to add "no auto-summary" command to disable RIPv2's "Classful behavior"!

R2>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 2 subnets
R       10.1.1.0 [120/1] via 172.30.2.1, 00:00:12, Serial0/0/0
R       10.2.2.0 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1
     172.30.0.0/24 is subnetted, 3 subnets
R       172.30.1.0 [120/1] via 172.30.2.1, 00:00:12, Serial0/0/0
C       172.30.2.0 is directly connected, Serial0/0/0
C       172.30.3.0 is directly connected, FastEthernet0/0
C    192.168.4.0/24 is directly connected, Serial0/0/1
R    192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1
R2>