CISCO_4006 layer three

[arifkh11896]

Dear Support personnel

I am facing network break problem in my network. I have a layer three switch on which static routes are defined.

and proxy server cyberoam is connected with cisco 4000 series switch. when i telnet our centrel switch cisco 4006

i received messages like this

n port 1/1 and port 2/12
2010 Apr 20 11:33:54 %SYS-4-P2_WARN: 1/Host 00:0d:54:81:f4:c0 is flapping betwee
n port 2/12 and port 1/1
2010 Apr 20 11:34:16 %SYS-4-P2_WARN: 1/Host 00:0d:54:81:f4:c0 is flapping betwee
n port 2/12 and port 1/1
2010 Apr 20 11:36:17 %SYS-4-P2_WARN: 1/Host 00:0d:54:81:f4:c0 is flapping betwee
n port 2/12 and port 1/1
2010 Apr 20 11:36:26 %SYS-4-P2_WARN: 1/Host 00:0d:54:81:f4:c0 is flapping betwee
n port 2/12 and port 1/1

where as  this MAC address is our layer three switch mac address where routes are defined.

when this message comes our network discoonected for a moment.

pls help me out with this problem.

[Giuseppe Larosa]

Hello Arif,

what is connected on ports 1/1 and 2/12 ?

what is the output of

sh spantree 1/1

sh spantree 2/12

Hope to help

Giuseppe

[arifkh11896]

Dear Thanks

1/1 is connected with layer three switch and 2/12 is connected with a L2

switch on which

cyberoam server is connected.

thanks

Arif

[Giuseppe Larosa]

Hello Arif,

the L2 switch connected to port 2/12 has a link to L3 switch. I mean another link?

is the L2 switch a manageable switch you can access to check configuration and log messages?

Hope to help

Giuseppe

[arifkh11896]

L2 switch has no another link

L2 switch is conneted with cyberoam proxy server.

L2 switch is 3com 4226t and there is not any logmessages.

[gchevalley]

You have a loop in your network that is being partially blocked by BPDUGuard.  BPDUGuard may be detecting the issue and disabling the port but not before the mac address is learned on the port.  Once the port learns the mac address is will propagate through you network on all trunk ports back the your core switch.  You will usually see this error for about 5 mintues until the mac address ages out. This can be caused by a user connecting the computer port of a Cisco IP Phone to an available wall jack or by a damaged cable receiving cross talk.  If those two ports are both trunk, you need to trace the issue back to the access layer switch the issue is occuring.  I have experienced this issue with the mac address of my file server all the sudden appearing on the other side of my campus.

[arifkh11896]

Yes I know there is some loop in my network .

But could you help me find out a loop in my network .

Actually we have a big network having cisco 3com and enterasys switches.

how can we find out loops.