Cisco WAN Switching Modules

Field Notice: BPX Unable to Reroute Connections to a Trunk with the Maximum Channels Set to a Maximum Value

February 17, 1999

Products Affected


Problem Description

BPX connections will not route if the best path is over a BXM trunk that has been configured to use the maximum number of channels supported by the BXM card.

Connections may take longer to route (up to 5 times longer) over a BXM trunk that has been configured to use one less than the maximum number of channels supported by the BXM card.

The channels configured for a BXM trunk can be verified or changed with the "Max Channels/Port" field on the cnftrk command display.

Problem Symptoms

Connections take excessively long to route or fail to route.


This problem affects networks with BPX nodes running with software release 8.4.xx and BXM cards configured at or near the maximum number of connection channels available on the card. The problem is not observed at the default number of channels which is 256.

This defect has Cisco bug ID CSCdk38852. If you are a registered CCO user and you have logged in, you can view the bug details.

View CSCdk38852 (registered customers only)


To avoid this problem, do not configure the maximum number of connection channels on the trunk to be more than the maximum supported by the port/trunk minus 29. 29 is the maximum routing bundle which is configured using the cnfcmparm command.


To determine the maximum number of channels supported by the port/trunk on a particular BXM card, use the cnftrk command to configure the maximum to be much greater than the expected maximum. For example, attempt to configure 15000 connection channels, as shown below:

This Command: cnftrk 2.1 9600 1000 7F Max Channels/Port (256): 15000

The software provides an error message with the maximum value that can be configured, as shown below:

PVC channels exceeds total card channels, avail: 13080 Max Channels/Port (256):

Due to the defect, the maximum value (13080 in the example above) will result in connections not routing. To workaround this defect, subtract 29 from the maximum value provided by the software and enter that value (13057 in the example above) as the "Max Channels/Port," as shown below:

TRK 2.1 Config T3 [9509 cps] BXM slot: 2
Transmit Rate: 9600 Line framing: PLCP
Subrate interface: -- coding: --
Subrate data rate: -- CRC: --
Line DS-0 map: -- recv impedance: --
Statistical Reserve: 1000 cps cable type: --
Idle code: 7F hex length: 0-225 ft.
Max Channels/Port: 13057 Pass sync: Yes
Connection Channels: 13057 Loop clock: No
Valid Traffic Classes: HCS Masking: Yes
V,TS,NTS,FR,FST,CBR,VBR,ABR Payload Scramble: No
SVC Channels: 0 Frame Scramble: --
SVC Bandwidth: 0 cps Virtual Trunk Type: --
Restrict CC traffic: No Virtual Trunk VPI: --
Link type: Terrestrial Deroute delay time: 0 seconds

Last Command: cnftrk 2.1 9600 1000 7f 13057 V,TS,NTS,FR,FST,CBR,VBR,ABR 0 0 N TE

Note: This defect does not exist in software releases 8.5 or later.

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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