Discontiguous networks still advertised ?

Answered Question
Feb 21st, 2010

I have a network with 4 routers all running EIGRP. I added 2 discontiguous networks, and EIGRP is distributing those networks as valid routes. It was my understanding that the only way this is supposed to work is if auto-summary is disabled. What am I overlooking? I have run no auto-summary on all the routers but the discontiguous network is still being distributed in all routing tables. (?)

RE#sh ip protocols
Routing Protocol is "eigrp 10"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 10
Automatic network summarization is in effect
Routing for Networks:
10.0.0.0
Routing Information Sources:
Gateway Distance Last Update
10.0.32.1 90 00:05:56
10.0.128.1 90 00:05:56
Distance: internal 90 external 170
RE#sh 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
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, * - candidate default
U - per-user static route
Gateway of last resort is not set
10.0.0.0/20 is subnetted, 3 subnets
D 10.0.16.0 [90/2681856] via 10.0.32.1, 00:12:52, Serial1
C 10.0.32.0 is directly connected, Serial1
C 10.0.128.0 is directly connected, Serial0
D 192.168.32.0/24 [90/2707456] via 10.0.32.1, 00:11:39, Serial1
D 192.168.33.0/24 [90/2172416] via 10.0.128.1, 00:11:00, Serial0

Correct Answer by Jon Marshall about 6 years 12 months ago

stevec90@yahoo.com

I have a network with 4 routers all running EIGRP. I added 2 discontiguous networks, and EIGRP is distributing those networks as valid routes. It was my understanding that the only way this is supposed to work is if auto-summary is disabled. What am I overlooking? I have run no auto-summary on all the routers but the discontiguous network is still being distributed in all routing tables. (?)

RE#sh ip protocols
Routing Protocol is "eigrp 10"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 10
Automatic network summarization is in effect
Routing for Networks:
10.0.0.0
Routing Information Sources:
Gateway Distance Last Update
10.0.32.1 90 00:05:56
10.0.128.1 90 00:05:56
Distance: internal 90 external 170
RE#sh 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
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, * - candidate default
U - per-user static route
Gateway of last resort is not set
10.0.0.0/20 is subnetted, 3 subnets
D 10.0.16.0 [90/2681856] via 10.0.32.1, 00:12:52, Serial1
C 10.0.32.0 is directly connected, Serial1
C 10.0.128.0 is directly connected, Serial0
D 192.168.32.0/24 [90/2707456] via 10.0.32.1, 00:11:39, Serial1
D 192.168.33.0/24 [90/2172416] via 10.0.128.1, 00:11:00, Serial0

Steve

Summary or no auto-summary will make no difference with 192.168.x.0/24 networks because there is no summarising to be done on these networks ie. they are class C networks anyway. Summarisation happens on classful boundaries but 192.168.32.0/24 and 192.168.33.0/24 are classful ie. class C networks.

If you want to test try using 172.16.x.0/24 networks because this is a class B network ie. 172.16.0.0/16.

Jon

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Correct Answer
Jon Marshall Sun, 02/21/2010 - 16:23

stevec90@yahoo.com

I have a network with 4 routers all running EIGRP. I added 2 discontiguous networks, and EIGRP is distributing those networks as valid routes. It was my understanding that the only way this is supposed to work is if auto-summary is disabled. What am I overlooking? I have run no auto-summary on all the routers but the discontiguous network is still being distributed in all routing tables. (?)

RE#sh ip protocols
Routing Protocol is "eigrp 10"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 10
Automatic network summarization is in effect
Routing for Networks:
10.0.0.0
Routing Information Sources:
Gateway Distance Last Update
10.0.32.1 90 00:05:56
10.0.128.1 90 00:05:56
Distance: internal 90 external 170
RE#sh 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
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, * - candidate default
U - per-user static route
Gateway of last resort is not set
10.0.0.0/20 is subnetted, 3 subnets
D 10.0.16.0 [90/2681856] via 10.0.32.1, 00:12:52, Serial1
C 10.0.32.0 is directly connected, Serial1
C 10.0.128.0 is directly connected, Serial0
D 192.168.32.0/24 [90/2707456] via 10.0.32.1, 00:11:39, Serial1
D 192.168.33.0/24 [90/2172416] via 10.0.128.1, 00:11:00, Serial0

Steve

Summary or no auto-summary will make no difference with 192.168.x.0/24 networks because there is no summarising to be done on these networks ie. they are class C networks anyway. Summarisation happens on classful boundaries but 192.168.32.0/24 and 192.168.33.0/24 are classful ie. class C networks.

If you want to test try using 172.16.x.0/24 networks because this is a class B network ie. 172.16.0.0/16.

Jon

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