USL Task? C5 Switches


We are chasing high system utilization rates at our central location. When the CPU rate is low (between 5-15%) there is no TID named USL Task. When CPU runs high (between 94-98%) there is a TID named USL Tack running between 50-80%.

We have found many errors, loops, rogue APs, even a hub! After finding each of these our rmon stats broadcast/multicast numbers dropped and out CPU numbers came down to 5-15%. USL Task would go away. Check an hour later and the USL Task is back, churning up 50-75%, and CPU is hovering in the mid 90s. When it peggs at 100% things get really ugly since this is the main egress from the entire school district.

What is USL Task and what can I learn from it?

4 replies

Sounds like you still have a loop.

https://extremeportal.force.com/ExtrArticleDetail?n=000004301&q=USL%20Task
Do you have STP enabled? If you do, on the edge port, enable adminedge

so you would

set spantree adminedge ge.1.1-47 true
set spantree spangaurd enable

Don't put adminedge on the non-edge ports. It will disable the port if it receives a BPDU.
Spantree is enabled. Adminedge "should" be set on all non-edge ports. show spantree debug no longer shows any spantree issues. No adminedge ports are blocked. Only one loop has triggered spantree to this point.

We found a hub because of the number of collisions in rmon stats for that port (spantree wont pick up a hub - no bpdu's). This helped. A few days later CPU was pegged again and we found a loop in another switch in the subnet. Two of us have been combing through the 6 closets (with about 2-3 switches each) at this location for the past few days.

If USL Task is an indicator of a loop, we will keep looking for loops.
Userlevel 7
Hi Joshua,

you can try broadcast limiters to limit the effect of loops and help in finding them (look for ports with high broadcast numbers).
set port broadcast [/code]But this might not be enough to completely mitigate a loop, see Port Broadcast Suppression does not help prevent network congestion on SecureStack during loop or flood.

You can limit flooded multicast and unknown unicast frames using the flood-ctrl feature set.

Erik

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