Information Technology Reference
In-Depth Information
Use the
show mls notification
and
show looktable
commands on the switch to point you
in the right direction of the duplicate MAC address or physical loop. The first will provide
a TA value; the command
show looktable <TA value>
will return a possible MAC address
that may be traced to the root of the problem.
Tips
Commands or Screen Captures
For descriptions and detailed examples of IP MLS router and switch commands, refer to the excellent
documentation listed under the “Additional Sources” section.
Before Calling Cisco Systems' TAC Team
Before calling Cisco Systems's Technical Assistance Center (TAC), make sure you that have read
through this chapter and completed the actions suggested for your system's problem.
Additionally, do the following and document the results so that we can better assist you:
•
Capture the output of
show module
from all the affected switches.
•
Capture the output of
show vtp domain
from all the affected switches.
•
Capture the output of
show trunk <mod_num/port_num>
from all the affected ports.
•
Capture the output of
show port <mod_num/port_num> capabilities
from all the affected ports.
•
Capture the output of
show tech-support
from the MLS-RP.
•
Capture the output of
show mls rp
on the MLS-RP and both
show mls
and
sh mls include
on the
MLS-SEs.
•
The output of additional commands may be necessary, depending on the nature of the issue.
A clear network topology and dial-in or Telnet access also help considerably in effective problem
resolution.
Troubleshooting Spanning-Tree Protocol and Related Design
Considerations
The text in this section comes directly from the Cisco web site
www.cisco.com/warp/customer/473/16.html.
Note
The primary function of the Spanning-Tree Algorithm (STA) is to cut loops created by redundant links
in bridged networks. The Spanning-Tree Protocol (STP) operates at Layer 2 of the OSI model and, by
the means of bridge protocol data units (BPDUs) exchanged between bridges, elects the ports that will
eventually forward or block traffic. This protocol can fail in some specific cases, and troubleshooting the
resulting situation can be very difficult, depending on the design of the network. We can even say that
in this particular area, the most important part of the troubleshooting is done before the problem occurs.
