March 13, 1998
BXM-622 cards at firmware revision MBV
BXM-155 cards at firmware revision MBV
BXM-T3/E3 cards at firmware revision MBV
Issuing a addlnlocrmtlp command on affected BXM cards (see revisions above), in a specific network topology, may cause network-wide node aborts. Earlier and later versions of BXM firmware do not exhibit this problem.
This problem occurs when a node is connected to the network through a single trunk as shown below:
Certain network messaging channels (status update messages not terminating on this node) are normally looped back at the ingress to the BPX backplane as shown in the diagram below:
When a addlnlocrmtlp command is issued on a BXM card, traffic is looped back to the card at the port interface. Traffic is also bridged onto the outbound trunk. This is shown in the diagram below:
When the addlnlocrmtlp command is issued on the BXM, the BXM sends a line status change message (cell) on the outbound trunk to inform its neighbor node of the change in status on its trunk interface. Because of the addlnlocrmtlp command loopback, this cell also gets looped back into the local BXM card. Since this status update message does not terminate on this node, it is again looped back at the backplane. This cycle repeats over and over - the status update message cell circulates within the BXM card at line rate. Each time the cell circulates, a copy is also being sent out on the outbound trunk. The problem is that the node at the other end of the trunk is not able to process status update changes at line rate and so it aborts. Since these status update messages are being propagated around the network, other nodes in the network may also abort.
The immediate solution is avoid issuing the addlnlocrmtlp command on BXM cards having firmware revision MBW.
The long-term solution will be to upgrade the BXM firmware to revision MBW. Firmware revision MBW removes bridging to the outbound trunk, thus preventing status update cells from going to the other node. The other node will eventually detect a com-break on its own.
BXM firmware revision MBW is available on the Cisco corporate ftp site. Use the path /cisco/wan/firmware/bpx/bxm-modelb/ to locate and download the file. If you need more information or assistance, call the Cisco Technical Assistance Center (TAC).
For More Information
If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:
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