C4K_EBM-4-HOSTFLAPPING error and %ETHC-5-PORTFROMSTP

[agarrett]

C4K_EBM-4-HOSTFLAPPING Host 00:90:4B:9B:2B:BB in vlan 11 is flapping between port Gi2/2 and port Fa5/1

This error, on a Distribution Layer Cat4006, led me back to the Core where I found this happening:

Core_6509_1> (enable) 2005 Jun 09 15:33:14 Pacific -07:00 %ETHC-5-PORTFROMSTP:Port 3/9 left bridge port 3/9

2005 Jun 09 15:33:14 Pacific -07:00 %DTP-5-NONTRUNKPORTON:Port 3/9 has become non-trunk

2005 Jun 09 15:33:18 Pacific -07:00 %DTP-5-TRUNKPORTON:Port 3/9 has become dot1q trunk

2005 Jun 09 15:33:30 Pacific -07:00 %ETHC-5-PORTTOSTP:Port 3/9 joined bridge port 3/9

It looks like an STP issue. Just started today.

I've been sitting here watching the port sporadically drop off (light goes out) and come back a second later and more error messages like the one above.

I can't narrow this down.

Anybody familiar with this flapping condition?

Al

[Georg Pauwen]

Hello Al,

my guess is that the problem is related to the DTP negotiation, try to turn DTP off alltogether on your trunks by configuring the ´switchport mode trunk´ and ´switchport nonegotiate´ commands on your trunk interfaces.

Also, are there wireless clients connected to your network ? If so, that could explain the ´host flapping´ log entries, AFAIK these would then be normal messages caused by wireless clients moving between access points...

Regards,

GP

[frenzeus]

Hi,

set trunk mod/port nonegotiate for CatOS. Anyways, for the flapping host, i've encountered numerous times, and in most cases in that network environment, there was a loop.. resulting with a broadcast storm, causing the host flapping messages.

I would look at the syslog and identify which switch is logging most of these messages and nail down on that switch. Check for cdp neighbors and spanning tree port states to identify funnies on that switch.

HTH.

[glen.grant]

I would look for physical layer problems on these links , looks like the link itself is flapping , look for crc's and things like that . If you are getting a lot of errors then the trunk is going to drop along with causing spanning tree to run . Look for cable or fiber issues or transciever issues if any of those are being used . I tend to disagree on hardcoding the trunks to on as this can mask problems . We have always let them negotiate the link without a problem .