Troubleshooting

Unusual Network Activity

Fast-Uplink Troubleshooting. Some of the problems that can result from incorrect usage of Fast-Uplink STP include temporary loops and generation of duplicate packets.

Problem sources can include:

Fast-Uplink is configured on a switch that is the STP root device.

Either the Hello Time or the Max Age setting (or both) is too long on one or more switches. Return the Hello Time and Max Age settings to their default values (2 seconds and 20 seconds, respectively, on a switch).

A “downlink” port is connected to a switch that is further away (in hop count) from the root device than the switch port on which fast-uplink STP is configured.

Two edge switches are directly linked to each other with a fast-uplink (Mode = Uplink) connection.

Fast uplink is configured on both ends of a link.

A switch serving as a backup STP root switch has ports configured for fast-uplink STP and has become the root device due to a failure in the original root device.

SSH-Related Problems

Switch access refused to a client. Even though you have placed the cli­ ent’s public key in a text file and copied the file (using the copy tftp pub-key- file command) into the switch, the switch refuses to allow the client to have access. If the source SSH client is an SSHv2 application, the public key may be in the PEM format, which the switch (SSHv1) does not interpret. Check the SSH client application for a utility that can convert the PEM-formatted key into an ASCII-formatted key.

Executing ip ssh does not enable SSH on the switch. The switch does not have a host key. Verify by executing show ip host-public-key. If you see the message

ssh cannot be enabled until a host key is configured (use 'crypto' command).

then you need to generate an SSH key pair for the switch. To do so, execute crypto key generate. (Refer to “2. Generating the Switch’s Public and Private Key Pair” in the Access Security Guide for your switch.)

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