If not configured properly, the STP (Spanning Tree Protocol) can create loops in a network.
Should these loops develop, they can cause network degradation and eventually crash the network by duplicating too many Ethernet frames. By leveraging Universal Port and the Extreme Loop Recovery Protocol (ELRP) as shown in example below, it is not only possible to detect and isolate the egress port, but it is also possible to disable the egress port to break loops.
Note
This example illustrates how to create an event profile that reconfigures the switch after an event. After this example was created, ELRP was updated with the capability to disable a port without the help of an event profile. For more information, see Using ELRP to Perform Loop Tests.
When a loop is detected on ports where ELRP is enabled and configured, ELRP logs a message using the following format:
01/17/2008 08:08:04.46 <Warn:ELRP.Report.Message> [CLI:ksu:1] LOOP DETECTED : 436309 transmited, 64 received, ingress slot:port (1) egress slot:port (24)
To view more information on format of this command, enter the show log events command as shown in the following example:
* BD8810-Rack2.6 # show log events "ELRP.Report.Message" details Comp SubComp Condition Severity Parameters ------- ----------- ----------------------- ------------- ---------- ELRP Report Message Warning 8 total 0 - string 1 - string 2 - number (32-bit unsigned int) 3 - string 4 - number (32-bit unsigned int) 5 - number (unsigned int) 6 - string 7 - string "[%0%:%1%:%2%] %3% : %4% transmited, %5% received, ingress slot:port (%6%) egress slot:port (%7%)"
In the example log statement, the VLAN (Virtual LAN) ksu, the ports is all, and the interval is “1.”
If a loop is detected, we want to disable the egress port on which the ELRP control packets went out. In this example, we enable ELRP on all ports of a VLAN as follows:
configure elrp-client periodic vlan ports all interval 1 seconds
We want the profile to disable egress ports 1 and 24 (which have been configured for loop). If we enable ELRP on only one port, then the port alone would be disabled.
We observe that parameter 7 is the one we have to disable from the above log message and the details for that event.
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