Possible Problem


End system not generating explorer traffic

Encapsulation mismatch

Hop count exceeded

Step 1 Use the show source-bridge privileged exec command to see whether the explorer count is incrementing.

Step 2 If the explorer count is not incrementing, use the show running-config privileged exec command to view the router configuration. Check for a source-bridge spanning interface configuration command on the local and remote routers.

Step 3 If the source-bridge spanning command is not configured on the routers, configure it on the interfaces connecting the local and remote SRBs. This command is required if the end system is using single-route explorers. The command syntax is as follows:

source-bridge spanning bridge-group [path-cost path-cost] Syntax Description:

• bridge-group—Number in the range 1 to 9 that you choose to refer to a particular group of bridged interfaces.

• path-cost—(Optional) Path cost for a specified interface.

• path-cost—(Optional) Path cost for the interface. The valid range is 0 to 65535.


The following example adds Token Ring 0 to bridge group 1 and assigns a path cost of 12 to Token Ring 0:

interface tokenring 0 source-bridge spanning 1 path-cost 12

Step 1 Use the show interfaces exec command to verify that the interface and line protocol are up. If the status line indicates any other state, refer to Chapter 15, "Troubleshooting Serial Line Problems."

Step 2 Verify that the configured encapsulation type matches the requirements of the network to which the serial interface is attached.

For example, if the serial interface is attached to a leased line but the configured encapsulation type is Frame Relay, there is an encapsulation mismatch.

Step 3 To resolve the mismatch, change the encapsulation type on the serial interface to the type appropriate for the attached network.

Step 1 Use the show protocol route command to check the hop count values on routers and bridges in the path. Packets that exceed the hop count are dropped.

Alternatively, you can enable the debug source event privileged exec command to see whether packets are being dropped because the hop count has been exceeded.

Caution: Because debugging output is assigned high priority in the CPU process, it can render the system unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco technical support staff. Moreover, it is best to use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system

Step 2 Increase the hop count if it is less than the default value, 7. Otherwise, the network must be redesigned so that no destination is greater than 7 hops away.

1 TCP = Transmission Control Protocol

2 FST = Fast Sequenced Transport

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