SMLT and Cp-limit

[Mary]

Hi all,

I had the following problem on one of my customer's network :
- they have a Nortel device (ERS4550) SMLT connected to the core switches;
- a few days ago, there was a loop behind this device and, as CP-limit is enabled on the core switches, one of the core ERS shut down the SMLT port to this device due to excessive control frames (we can see this in the logs) but on other core ERS there is no such message (shutdown port x/y due to excessive control frames). But, on this second ERS we can see that the corresponding SMLT  is going down ..


Anyone know if this a normal behavior ? Any idea why the second ERS didn't shut down the corresponding SMLT port ?

Thanks.

Mary

[Michael McNamara]

Hi Mary and welcome to the forums!

Assuming that you the configuration is idential on the second ERS 8600 you probably didn't reach the threshold, hence the second ERS 8600 didn't shutdown the port. The default values for cp-limit are very high in my opinion and should be lowered as a best practice.

If you are referring to the log message "SMLT Down" on the second ERS 8600, that message will be logged on all IST peers anytime a SMLT connection goes into a non-SMLT configuration.

Example; if you have an ERS 4548 uplinked to two ERS 8600 switches from port 47 and 48; disable port 47 and you'll see "SMLT down" alarms on both ERS 8600 switches, this is to incidate that the port is no longer in SMLT mode but instead is just a normal uplink. This is necessary so the other ERS 8600 switch now knows to forward all traffic for the edge switch across the IST link which will ultimately get forwarded out to the closet on the remaining active uplink.

Good Luck!

[Michael McNamara]

Have a look at this thread for a good discussion of best practice values;

http://forums.networkinfrastructure.info/nortel-ethernet-switching/broadcast-and-multicast-rate-limit-values-best-practice/

Cheers!