Neighbor not on common subnet for Vlan 1

[dynamitec1]

Hello, I read a few discussions before posting this.  After a few days of reading the discussions and Cisco documentations, I'm still without a clue how to resolve this issues.  I'm not sure when did this started happening, I've only inherited this network.  We have a few more VLANs and only VLAN166 seems to be having an issue. I have no known server with DUAL-NIC under VLAN166, servers are on a totally different VLAN. No VLAN mismatch errors that I could see.

According to my SolarWinds, the CPU utilization for DISTRO-SW2 is at 27%. while four other DISTRO switch are at 0%

Perhaps someone can shed more light on this error:

********************************************

Neighbor 10.34.166.2 not on common subnet

Neighbor 10.34.166.3 not on common subnet

*******************************************

Catalyst C-6509

sup-bootflash:s72033-ipservices_wan-mz.122-33.SXI7.bin

DISTRO-SW2:

router eigrp 40

network 10.34.0.0

auto-summary

interface Vlan1

description MANAGEMENT

ip address 10.34.2.47 255.255.255.0

ip helper-address 10.34.251.66

no ip redirects

standby 1 ip 10.34.2.1

standby 1 priority 110

standby 1 preempt

end

interface Vlan166

description HAI DER

ip address 10.34.166.3 255.255.255.0

ip helper-address 10.34.251.66

no ip redirects

ip directed-broadcast 98

ip pim sparse-dense-mode

mls rp vtp-domain CISCO

mls rp ip

standby 166 ip 10.34.166.1

standby 166 priority 110

standby 166 preempt

end

DISTRO-SW1: sh int vlan166

router eigrp 40

network 10.34.0.0

auto-summary

interface Vlan1

description MANAGEMENT

ip address 10.34.2.24 255.255.255.0

ip helper-address 10.34.251.66

no ip redirects

standby 1 ip 10.34.2.1

standby 1 priority 115

standby 1 preempt

end

interface Vlan166

description HAI DER

ip address 10.34.166.2 255.255.255.0

ip helper-address 10.34.251.66

no ip redirects

ip directed-broadcast 98

ip pim sparse-dense-mode

mls rp vtp-domain CISCO

mls rp ip

standby 166 ip 10.34.166.1

standby 166 priority 115

standby 166 preempt

end

Thanks!

Adam

[Reza Sharifi]

Hi,

Can you try this EIGRP config on both switches and test again?

router eigrp 40

no auto-summary

network 10.34.2.0 0.0.0.255

network 10.34.166.0 0.0.0.255

HTH

[dslice]

Auto-summary is irrelevant with a single network statement/major net. The problem being reported is that an EIGRP hello is received on an interface with a different subnet assigned. Since that's not what the config looks like, I suspect you have some layer two problem causing he hellos to be received on incorrect interfaces. What does debug ip packet detail with an acl limiting it to only destination 224.0.0.10?

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[dynamitec1]

UPDATE:

I made no changes, but the error message has disappeared.

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[Giuseppe Larosa · Accepted solution]

Hello Adam,

as mentioned by Donald, somewhere in your switched network Vlan 1 and Vlan 166 were joined together and the EIGRP hello packets with a multicast destination were received on Vlan 1 SVI causing the error messages.

To be noted this can be caused by two switch ports configured and acting as access ports one in Vlan 1 and one in Vlan 166 connected together, not only by a native vlan mismatch on 802.1Q layer 2 trunks.

Is the cpu usage lower now on the device? Because you have also noted an higher cpu usage on the affected multilayer switch.

Hope to help

Giuseppe

[dynamitec1]

Giuseppe,

You guys are correct about VLAN 1 and VLAN 166 being joined together. I still didnt or couldnt find where it was in my network. But we have been replacing 2950s and 3500s the last few months. And, I wouldnt doubt if that was the case. There are lots of discrepancies with basic switch configs, as if they were installed 5 years ago and acting like a hub. SIGH*

Re: THE CPU

Im getting DRAM correctable error every 60-secs. It could be one of the SUP720 module that's causing this. Thoughts?

Thanks.

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[dynamitec1]

Theres only one bldg under VLAN166, the switches were replaced with new PoE switches in mid-Jan 2013. It wasnt until two weeks ago that we stopped getting the "neighbor not on common subnet" error.

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[Richard Burts · Accepted solution]

Adam

Almost certainly the problem was caused because somewhere two switches were cross connected. And the problem was resolved when someone corrected the connections.

HTH

Rick