Hi Peter,
> AFAIK all Cisco switches always send "Ethernet Loopback" (ethertype > 0x9000) packets on switchport interfaces and disable the port is things > loop. Loops would result in a message like this: > > %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on > FastEthernet0/37 > > This would possibly be followed by: > > %PM-4-ERR_DISABLE: loopback error detected on Fa0/37, putting Fa0/37 in > err-disable state > Using an old switch I have in my lab : Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6, RELEASE SOFTWARE (fc1) If I connect an unmanged 8 port switch to cat3550-0/1 and once it is connected create a loop on the 8 port switch: *Mar 1 02:15:32.811: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up *Mar 1 02:15:33.811: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down *Mar 1 02:15:34.819: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up *Mar 1 02:17:29.003: %SYS-2-MALLOCFAIL: Memory allocation of 1692 bytes failed from 0x158568, alignment 0 Pool: I/O Free: 21284 Cause: Memory fragmentation Alternate Pool: None Free: 0 Cause: No Alternate pool -Process= "Pool Manager", ipl= 0, pid= 5 *Mar 1 02:17:35.515: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down *Mar 1 02:17:40.779: %PM-4-ERR_DISABLE: dtp-flap error detected on Fa0/1, putting Fa0/1 in err-disable state *Mar 1 02:17:42.791: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to down However, if the loop already exists on the unmanged 8 port switch: *Mar 1 02:34:01.099: %SYS-2-MALLOCFAIL: Memory allocation of 1692 bytes failed from 0x158568, alignment 0 Pool: I/O Free: 21284 Cause: Memory fragmentation Alternate Pool: None Free: 0 Cause: No Alternate pool -Process= "Pool Manager", ipl= 0, pid= 5 *Mar 1 02:34:02.199: %LINK-3-UPDOWN: Interface FastEthernet0/17, changed state to up *Mar 1 02:34:03.211: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/17, changed state to up *Mar 1 02:34:31.103: %SYS-2-MALLOCFAIL: Memory allocation of 1692 bytes failed from 0x158568, alignment 0 Pool: I/O Free: 21284 Cause: Memory fragmentation Alternate Pool: None Free: 0 Cause: No Alternate pool -Process= "Pool Manager", ipl= 0, pid= 5 *Mar 1 02:35:01.151: %SYS-2-MALLOCFAIL: Memory allocation of 1692 bytes failed from 0x158568, alignment 0 Pool: I/O Free: 21284 Cause: Memory fragmentation Alternate Pool: None Free: 0 Cause: No Alternate pool -Process= "Pool Manager", ipl= 0, pid= 5 So unfortunately on this old switch the port only goes down if the loop occurs after the interface comes up on the Cisco. I will try this with a newer switch which has the "ETHCNTR-3-LOOP_BACK_DETECTED" feature in the next few days. Thanks again, Andrew _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
