Auto-summary and routing tables

kinellkinell Member Posts: 6 ■□□□□□□□□□
in CCNA & CCENT
Im doing a RIPv2 LAB on my gear and something weird is happening with auto-summary.


This is the scenario:





And these are the routing tables:

auto-summary OFF:



[SIZE=1]WEST#sh ip route[/SIZE]
[SIZE=1]Gateway of last resort is not set[/SIZE]
[SIZE=1]
[/SIZE]
[SIZE=1]C    172.16.0.0/16 is directly connected, FastEthernet0/0[/SIZE]
[SIZE=1]    10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]R       10.1.1.8 [120/1] via 10.1.1.13, 00:00:06, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.12 is directly connected, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.0 [120/2] via 10.1.1.13, 00:00:06, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.4 [120/1] via 10.1.1.13, 00:00:06, Serial0/1[/SIZE]
[SIZE=1]R    192.168.1.0/24 [120/2] via 10.1.1.13, 00:00:06, Serial0/1[/SIZE]


[SIZE=1]NORTH#sh ip route[/SIZE]
[SIZE=1]Gateway of last resort is not set[/SIZE]
[SIZE=1]
[/SIZE]
[SIZE=1]R    172.16.0.0/16 [120/2] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]    10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]C       10.1.1.8 is directly connected, Serial0/0[/SIZE]
[SIZE=1]R       10.1.1.12 [120/1] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]C       10.1.1.0 is directly connected, Serial0/2[/SIZE]
[SIZE=1]R       10.1.1.4 [120/1] via 10.1.1.2, 00:00:02, Serial0/2[/SIZE]
[SIZE=1]                [120/1] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]R    192.168.1.0/24 [120/1] via 10.1.1.2, 00:00:02, Serial0/2[/SIZE]




[SIZE=1]HQ#sh ip route[/SIZE]
[SIZE=1]Gateway of last resort is not set[/SIZE]
[SIZE=1]
[/SIZE]
[SIZE=1]R    172.16.0.0/16 [120/1] via 10.1.1.14, 00:00:08, Serial0/0[/SIZE]
[SIZE=1]    10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]C       10.1.1.8 is directly connected, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.12 is directly connected, Serial0/0[/SIZE]
[SIZE=1]R       10.1.1.0 [120/1] via 10.1.1.10, 00:00:01, Serial0/1[/SIZE]
[SIZE=1]                [120/1] via 10.1.1.6, 00:00:01, Serial0/2[/SIZE]
[SIZE=1]C       10.1.1.4 is directly connected, Serial0/2[/SIZE]
[SIZE=1]R    192.168.1.0/24 [120/1] via 10.1.1.6, 00:00:01, Serial0/2[/SIZE]


[SIZE=1]SOUTH#sh ip route[/SIZE]
[SIZE=1]Gateway of last resort is not set[/SIZE]
[SIZE=1]
[/SIZE]
[SIZE=1]R    172.16.0.0/16 [120/2] via 10.1.1.5, 00:00:18, Serial0/1[/SIZE]
[SIZE=1]    10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]R       10.1.1.8 [120/1] via 10.1.1.1, 00:00:13, Serial0/2[/SIZE]
[SIZE=1]                [120/1] via 10.1.1.5, 00:00:18, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.12 [120/1] via 10.1.1.5, 00:00:18, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.0 is directly connected, Serial0/2[/SIZE]
[SIZE=1]C       10.1.1.4 is directly connected, Serial0/1[/SIZE]
[SIZE=1]C    192.168.1.0/24 is directly connected, FastEthernet0/0[/SIZE]





auto-summary ON:



[SIZE=1]WEST#sh ip route
[/SIZE][SIZE=1]Gateway of last resort is not set[/SIZE][SIZE=1]
[/SIZE]
[SIZE=1]C    172.16.0.0/16 is directly connected, FastEthernet0/0[/SIZE]
[SIZE=1]     10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]R       10.1.1.8 [120/1] via 10.1.1.13, 00:00:20, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.12 is directly connected, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.0 [120/2] via 10.1.1.13, 00:00:20, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.4 [120/1] via 10.1.1.13, 00:00:20, Serial0/1[/SIZE]
[COLOR=#ff0000][SIZE=1]R    192.168.1.0/24 [120/1] via 10.1.1.13, 00:00:20, Serial0/1[/SIZE][/COLOR]


[SIZE=1]NORTH#sh ip route
[/SIZE][SIZE=1]Gateway of last resort is not set[/SIZE][SIZE=1]
[/SIZE]
[COLOR=#ff0000][SIZE=1]R    172.16.0.0/16 [120/1] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE][/COLOR]
[SIZE=1]     10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]C       10.1.1.8 is directly connected, Serial0/0[/SIZE]
[SIZE=1]R       10.1.1.12 [120/1] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]C       10.1.1.0 is directly connected, Serial0/2[/SIZE]
[SIZE=1]R       10.1.1.4 [120/1] via 10.1.1.2, 00:00:12, Serial0/2[/SIZE]
[SIZE=1]                     [120/1] via 10.1.1.9, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]R    192.168.1.0/24 [120/1] via 10.1.1.2, 00:00:12, Serial0/2[/SIZE]




[SIZE=1]HQ#sh ip route
[/SIZE][SIZE=1]Gateway of last resort is not set[/SIZE]

[COLOR=#ff0000][SIZE=1]R    172.16.0.0/16 [120/1] via 10.1.1.14, 00:00:14, Serial0/0[/SIZE]
[SIZE=1]                        [120/1] via 10.1.1.6, 00:00:16, Serial0/2[/SIZE][/COLOR]
[SIZE=1]     10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]C       10.1.1.8 is directly connected, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.12 is directly connected, Serial0/0[/SIZE]
[SIZE=1]R       10.1.1.0 [120/1] via 10.1.1.10, 00:00:13, Serial0/1[/SIZE]
[SIZE=1]                 [120/1] via 10.1.1.6, 00:00:16, Serial0/2[/SIZE]
[SIZE=1]C       10.1.1.4 is directly connected, Serial0/2[/SIZE]
[COLOR=#ff0000][SIZE=1]R    192.168.1.0/24 [120/1] via 10.1.1.6, 00:00:16, Serial0/2[/SIZE]
[SIZE=1]                         [120/1] via 10.1.1.10, 00:00:14, Serial0/1[/SIZE][/COLOR]


[SIZE=1]SOUTH#sh ip route
[/SIZE][SIZE=1]Gateway of last resort is not set[/SIZE][SIZE=1]
[/SIZE]
[COLOR=#ff0000][SIZE=1]R    172.16.0.0/16 [120/1] via 10.1.1.1, 00:00:05, Serial0/2[/SIZE][/COLOR]
[SIZE=1]     10.0.0.0/30 is subnetted, 4 subnets[/SIZE]
[SIZE=1]R       10.1.1.8 [120/1] via 10.1.1.1, 00:00:05, Serial0/2[/SIZE]
[SIZE=1]                    [120/1] via 10.1.1.5, 00:00:03, Serial0/1[/SIZE]
[SIZE=1]R       10.1.1.12 [120/1] via 10.1.1.5, 00:00:03, Serial0/1[/SIZE]
[SIZE=1]C       10.1.1.0 is directly connected, Serial0/2[/SIZE]
[SIZE=1]C       10.1.1.4 is directly connected, Serial0/1[/SIZE]
[SIZE=1]C    192.168.1.0/24 is directly connected, FastEthernet0/0[/SIZE]






As you can see, it's a basic topology and auto-summary shouldn't have any effect on the routing tables, but something is happening with routes and specifically with hops to 192.168.1.0 & 172.16.0.0.


In Packet Tracer there are no effect on the routing tables with auto-summary ON (as expected), only in a real gear and GNS3 they change with auto-summary ON.


There is something that I'm missing?
Could be an IOS bug?
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Comments

  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    Summarization can impact the hop-count and there have been bugs in the RIP auto-summary command.

    Before I consider further, in the second topology are you certain you have "version 2" and "auto-summary" enabled on all four routers? Which version of IOS are you using?
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  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    I just verified in 12.4(15)T14 in this scenario I see the top output only w/ auto-summary enabled..

    ..which confirms you either have a misconfiguration or a buggy version of IOS.
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  • kinellkinell Member Posts: 6 ■□□□□□□□□□
    Yes, you are right, I've been using an old IOS (12.3-26), now tested in 124-15.T14 and auto-summary had no effect on routing tables.
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