How Cisco switches Find loops and workarounds

how Cisco switches Find loops and workarounds

How can I intuitively and quickly determine if a Cisco switch has a loop? and quickly locate the switch loop location? This becomes a problem?

Loop view there is currently no best way to visually view only through some information. There are many prevention loop commands in the Cisco environment in addition to spanning trees. The loop generates a broadcast storm that can seriously cause contact blocking, the switch sends a hint when the loop occurs, and can be found through the network management software, the log server, or the direct login switch, which allows you to find loops through show CDP in Cisco environments. Or visually observe if the switch interface LEDs are flashing, then tap show interface + an interface at the command line to see the traffic information for the interface. or directly typed in the command debug ARP. If the on-screen rapid display of n-more ARP information, note that it is quick to appear, not occasionally, then there must be a loop, then no debug arp, then can be turned off, and then look at the screen appears on the ARP information, the information will certainly contain the interface, and then check these interfaces, and finally determine. It is recommended to use the last one.

Technical Support:
1. If the access layer has a loop, such as the hub is short, it is bound to reflect the distribution layer switch, resulting in the distribution layer switch CPU high, this is positive. :

Command:

#show Processes CPU History

2. It is recommended to use the SolarWinds tool to monitor the CPU of all the distributed layer switches, and when a user in a zone responds slowly, first check the area distribution switch CPU utilization, and then see if there is such a record in the log:
Command:
#show Log

Feb 08:47:54 beijing:k_ebm-4-hostflapping:host 00:15:C6:0D:3F:BF in VLAN flapping between Port Po1 and Port Gi2 /1

3. Then in check the neighbor (G2/1) of the distributed layer switch, which switch is logged on to the Access layer switch:

Command:

#show CDP Neighbors

Check the log to see if there is err-disable log, of course, the premise is configured with this detection function, if there is no such hint
Use

#show Interfaces | In (is Up|5 min) to see which interface packet volume is huge, if this is a large number of port is not a cascade port, then congratulations, basically found the source.

4. If the distribution layer switch is more, repeat the above command repeatedly to find out the source location.

5. At this time, you can:
1, shutdown this interface
2, the implementation of storm control
3. Spanning-tree Host
Global Mode Open Bgdugard
The above three ways you can choose

Of course, the network devices in your LAN are Cisco, and other devices may not be the same, but the idea is similar.

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How Cisco switches Find loops and workarounds