BSCI Lab 7 - EIGRP Summarization
EIGRP: Understanding Summarization
Directions:
- Configure the network as per the diagram.
- On R1 create 4 Loopback interfaces (Loop0-Loop3) with an IP addressing scheme of 172.16.0.1/24, 172.16.1.1/24, 172.16.2.1/24, 172.16.3.1/24 respectfully.
- Configure EIGRP 100 on both routers.
- R3 should only receive a route of 172.16.0.0/22 for the loopback interfaces.
Solution
First configure the IP information on all routers.
R1(config)#int s0/0
R1(config-if)#ip add 74.66.22.9 255.255.255.252
R1(config-if)#no shut
R1(config-if)#int lo0
R1(config-if)#ip add 172.16.0.1 255.255.255.0
R1(config-if)#int lo1
R1(config-if)#ip add 172.16.1.1 255.255.255.0
R1(config-if)#int lo2
R1(config-if)#ip add 172.16.2.1 255.255.255.0
R1(config-if)#int lo3
R1(config-if)#ip add 172.16.3.1 255.255.255.0
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R3(config)#int s0/0
R3(config-if)#ip add 74.66.22.10 255.255.255.252
R3(config-if)#clock rate 64000
R3(config-if)#no shut
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Next we will configure EIGRP on both routers.
R2(config)#router eigrp 100
R1(config-router)#network 0.0.0.0
R1(config-router)#no auto
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Currently we see that R3 is receiving all 4 Loopback networks. We need to use summarization so that it only receives the one route. This will be configured on R1.
R3(config-router)#do show ip route eigrp
172.16.0.0/24 is subnetted, 4 subnets
D 172.16.0.0 [90/2297856] via 74.66.22.9, 00:00:09, Serial0/0
D 172.16.1.0 [90/2297856] via 74.66.22.9, 00:00:09, Serial0/0
D 172.16.2.0 [90/2297856] via 74.66.22.9, 00:00:09, Serial0/0
D 172.16.3.0 [90/2297856] via 74.66.22.9, 00:00:09, Serial0/0
R3(config-router)#
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The easiest way to calculate summarizations is to look at the addresses in binary form. To do this, first determine how many bits are the same between the addresses and rewrite the subnet mask
by counting up the matching bits. In this example, the only differences are in the 3rd octet. The first 6 digits match, but the 7th is different so the mask would be rewritten to 252.
172 = 10101100
172 = 10101100
172 = 10101100
172 = 10101100
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16 = 00010000
16 = 00010000
16 = 00010000
16 = 00010000 |
0 = 00000000
1 = 00000001
2 = 00000010
3 = 00000011 |
0 = 00000000
0 = 00000000
0 = 00000000
0 = 00000000
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| 11111111 = 255 |
11111111 = 255 |
11111100 = 252 |
00000000 = 0 |
Once we have figured out the summary mask for the network we need to configure the summary on R1's S0/0 interface. This is the interface that sends the update to R3.
R1(config-if)#ip summary-address eigrp 100 172.16.0.0 255.255.252.0
R1(config-if)#
*Mar 1 00:11:28.275: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 74.66.22.10 (Serial0/0) is resync: summary configured
R1(config-if)#
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After we configure the summary, we now see just one route on R3, but still have full reachability.
R3(config-router)#do show ip route eigrp
172.16.0.0/22 is subnetted, 1 subnets
D 172.16.0.0 [90/2297856] via 74.66.22.9, 00:00:08, Serial0/0
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