C-20
Troubleshooting
Unusual Network Activity
Fast-Uplink Troubleshooting.
Some of the problems that can result from
incorrect usage of Fast-Uplink MSTP include temporary loops and generation
of duplicate packets.
Problem sources can include:
■
Fast-Uplink is configured on a switch that is the MSTP 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
MSTP 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 MSTP root switch has ports configured for
fast-uplink MSTP 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
client’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 SSH chapter of the
Access Security Guide
for your switch.)
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 20 Monday, January 28, 2008 10:04 AM