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EIGRP not obeying auto-summary?

On my way to recreating an EIGRP scenario in one of my BSCI textbooks, I have R2 and R4 connected to each other via a 1MB back-to-back serial link, 131.108.255.0/30 (R2 is .1; R4 .2).

R2 has a whole slew of 24-bit loopbacks configured; and what's weird to me is that all of them are showing up as specific 24-bit networks in R4's routing table. Auto-summary has NOT been disabled on either router.

So am I misunderstanding something here; shouldn't the one 16-bit network 131.108.0.0 be the only one visible to R4, without the no auto-summary command configured?

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: EIGRP not obeying auto-summary?

Hello Stuey,

auto summary is triggered by a change of major network.

That is until you are within net 131.108.0.0 is legitimate and correct to see these specific routes.

change the link between the two devices in something not belonging to the same class B network and you will see the difference.

Hope to help

Giuseppe

7 REPLIES

Re: EIGRP not obeying auto-summary?

R4#sh ip pro

Routing Protocol is "eigrp 1"

Outgoing update filter list for all interfaces is

Incoming update filter list for all interfaces is

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 1

Automatic network summarization is in effect

Routing for Networks:

131.108.0.0

Routing Information Sources:

Gateway Distance Last Update

131.108.255.1 90 00:46:03

Distance: internal 90 external 170

R4#sh run

!

router eigrp 1

network 131.108.0.0

auto-summary

no eigrp log-neighbor-changes

!

Re: EIGRP not obeying auto-summary?

R2#sh ip pro

Routing Protocol is "eigrp 1"

Outgoing update filter list for all interfaces is

Incoming update filter list for all interfaces is

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 1

Automatic network summarization is in effect

Routing for Networks:

131.108.0.0

Routing Information Sources:

Gateway Distance Last Update

131.108.255.2 90 00:47:32

Distance: internal 90 external 170

R2#sh run

!

router eigrp 1

network 131.108.0.0

!

Re: EIGRP not obeying auto-summary?

What does your routing table look like?

what lab is it? Is it from the Cisco Lab Portfolio....if so, whats the lab number?

Re: EIGRP not obeying auto-summary?

It's from CCNP Practical Studies: Routing, by Henry Benjamin (2002, page 209)

I'm not a fan of Cisco Press books (50 typos or factual errors per page, seems to be their internal requirement), but I'm taking BSCI in November so I'm soaking up all the BSCI / advanced routing materials I can find....perhaps I should be more discriminate.

The routing table looks like this:

131.108.0.0/16 is variably subnetted, 18 subnets, 3 masks

C 131.108.255.0/30 is directly connected, Serial0

C 131.108.255.1/32 is directly connected, Serial0

D 131.108.31.0/24 [90/2297856] via 131.108.255.1, 01:13:28, Serial0

D 131.108.30.0/24 [90/2297856] via 131.108.255.1, 01:13:28, Serial0

D 131.108.29.0/24 [90/2297856] via 131.108.255.1, 01:13:28, Serial0

D 131.108.28.0/24 [90/2297856] via 131.108.255.1, 01:13:28, Serial0

D 131.108.27.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.26.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.25.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.24.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.23.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.22.0/24 [90/2297856] via 131.108.255.1, 01:13:29, Serial0

D 131.108.21.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

D 131.108.20.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

D 131.108.19.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

D 131.108.18.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

D 131.108.17.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

D 131.108.16.0/24 [90/2297856] via 131.108.255.1, 01:13:34, Serial0

C 222.1.8.0/24 is directly connected, Loopback0

R4>

Re: EIGRP not obeying auto-summary?

If this helps w/ anyone's diagnostic efforts, here are the IOS versions in play:

R2>sh version

Cisco Internetwork Operating System Software

IOS (tm) 2500 Software (C2500-I-L), Version 12.0(8), RELEASE SOFTWARE (fc1)

Copyright (c) 1986-1999 by cisco Systems, Inc.

Compiled Mon 29-Nov-99 13:23 by kpma

Image text-base: 0x0302F208, data-base: 0x00001000

ROM: System Bootstrap, Version 11.0(10c)XB1, PLATFORM SPECIFIC RELEASE SOFTWARE

(fc1)

BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c)XB1, PLATFORM

SPECIFIC RELEASE SOFTWARE (fc1)

R2 uptime is 5 hours, 11 minutes

System restarted by reload

System image file is "flash:c2500-i-l.120-8.bin"

cisco 2500 (68030) processor (revision M) with 14336K/2048K bytes of memory.

Processor board ID 06943704, with hardware revision 00000000

Bridging software.

X.25 software, Version 3.0.0.

1 Ethernet/IEEE 802.3 interface(s)

1 Token Ring/IEEE 802.5 interface(s)

2 Serial network interface(s)

32K bytes of non-volatile configuration memory.

16384K bytes of processor board System flash (Read ONLY)

Configuration register is 0x2102

R2>

R4>sh version

Cisco Internetwork Operating System Software

IOS (tm) 2500 Software (C2500-JK8OS-L), Version 12.2(1d), RELEASE SOFTWARE (fc1)

Copyright (c) 1986-2002 by cisco Systems, Inc.

Compiled Sun 03-Feb-02 22:01 by srani

Image text-base: 0x0307EEE0, data-base: 0x00001000

ROM: System Bootstrap, Version 11.0(10c)XB1, PLATFORM SPECIFIC RELEASE SOFTWARE

(fc1)

BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c)XB1, PLATFORM

SPECIFIC RELEASE SOFTWARE (fc1)

R4 uptime is 5 hours, 9 minutes

System returned to ROM by power-on

System image file is "flash:c2500-jk8os-l.122-1d.bin"

cisco 2521 (68030) processor (revision K) with 14336K/2048K bytes of memory.

Processor board ID 10353811, with hardware revision 00000003

Bridging software.

X.25 software, Version 3.0.0.

SuperLAT software (copyright 1990 by Meridian Technology Corp).

TN3270 Emulation software.

Basic Rate ISDN software, Version 1.1.

1 Token Ring/IEEE 802.5 interface(s)

2 Serial network interface(s)

2 Low-speed serial(sync/async) network interface(s)

1 ISDN Basic Rate interface(s)

32K bytes of non-volatile configuration memory.

16384K bytes of processor board System flash (Read ONLY)

Configuration register is 0x2102

R4>

I also tried the same thing on R1 and R3 and got the same result: a whole bunch of 24-bit subnets of 131.108 even with auto-summ left in effect on both. R1 has IOS Version 12.3(24); R4 (a 2522) has Version 12.0(8).

Thanks guys; I look forward to brilliant insights.

Re: EIGRP not obeying auto-summary?

Perhaps there isn't, in fact, a non-twilight-zone reason why this is happening.

Can someone out there at least confirm my suspicion, that I SHOULD NOT be seeing these 24-bit networks as EIGRP routes in R4's route table, under the current config?

Hall of Fame Super Silver

Re: EIGRP not obeying auto-summary?

Hello Stuey,

auto summary is triggered by a change of major network.

That is until you are within net 131.108.0.0 is legitimate and correct to see these specific routes.

change the link between the two devices in something not belonging to the same class B network and you will see the difference.

Hope to help

Giuseppe

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