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Community Member

cisco vlan problem - who is responding to an IP?

We have an interesting situation on a cisco catalyst 6509 running 12.2(17d)SXB1 (?).

Vlan 187 with an IP of

Interface 8/24 in vlan 187

Interface 8/39 vlan trunk with vlan 187 assigned.  no other vlans.

On a PC on vlan (external to catalyst) I can ping - MAC corresponds to catalyst.  Catalyst proxy arping for 170??

Telnet into catalyst

Shut down 8/24;  shut down 8/39;  ping 170 no response.  OK sounds good.  Find which interface 170 is on....

[meanwhile sho ip arp gives a mac for the address of the catalyst]

Turn up 8/24;  after 2 min, ping 170 response with mac of catalyst;  170 looks like it is on int 8/24?  but with mac of catalyst??

Shut down 8/24; Turn up 8/39; after 2 min, ping response with mac of catalyst.  170 looks like it is on 8/39?? but with mac of catalyst??

WHAT? ?????

I also turned off proxy-arp on vlan 187.  No difference above.  I rebooted the catalyst.  No difference.

We also shut down vlan 187 so the catalyst wouldn't know about  ping 170 doesn't work-catalyst send ping to default.  

Can you explain to me WHO/WHAT is responding to a ping to 170?  Why is this catalyst responding to 170?

There are no other 10.203.187 networks in other places, nothing shows in routing table. 

170 was assigned to a linux box before we did some reconfiguration on this vlan, and it worked fine.  Now the linux box refuses to come up and take 170 because somebody else "has the address."

Thanks for any ideas!!!

Cisco Employee

cisco vlan problem - who is responding to an IP?

Hi John,

honestly I would not waste too much time troubleshooting this issue on a box with a 8 years old software....

Why don't you upgrade to the latest available software for your supervisor (I guess it is pretty old too) and then you try again?

If you still have problems I will gladly help you out


Community Member

Re: cisco vlan problem - who is responding to an IP?

Thanks, figured I should do that. Looking now.


On Fri, Feb 17, 2012 at 10:59 AM, rsimoni <

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