[c-nsp] HP Loop-protect on Cisco

[Andrew Miehs]

 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