Campus Switching and Routing

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Mobility Access Switches - Error - Flushing port

Does know what this means?  I am reviewing the logs, and this is something that caught my attention.

 

 <WARN> |l2m|  Flushing port GE3/0/16

 

Thanks,

 

Dave Hall

Aruba

Re: Mobility Access Switches - Error - Flushing port

Dave,

That is log entry indicating that we are clearing the mac-address-table entries for a given port. You typically see it due to ports flapping which may result in STP Topology Change Notifications which is why we recommend enabling "portfast" on access ports.

 

Best regards,

 

Madani

Occasional Contributor II

Re: Mobility Access Switches - Error - Flushing port

What if you see it on trunk ports?

Aruba

Re: Mobility Access Switches - Error - Flushing port

Its for the same reason. The switch is receiving a TCN and so it is clearing the mac-address-table entries.

Occasional Contributor II

Re: Mobility Access Switches - Error - Flushing port

Is there a way to turn on port fast on a trunk port? I thought I read somewhere it is unavailable. If that's the case do we have to live with the errors?

Thanks
Aruba

Re: Mobility Access Switches - Error - Flushing port

Unfortunately not at this time. I recommened you submit a feature request via the Idea Portal.

 

https://arubanetworkskb.secure.force.com/cp/ideas/ideaList.apexp

 

I wouldn't describe these as errors but normal behavior as a result of a spanning-tree topology change. Are these trunks going to user devices as opposed to other switches and as such they may go up and down with great frequency? I'm trying to understand what is generating the STP changes.

 

Bst regards,

 

Madani

Occasional Contributor II

Re: Mobility Access Switches - Error - Flushing port

Thank you for your response. These are trunk ports connecting to Cisco 3560 switches and it is mainly just annoying getting these. By enabling the port fast on the access ports we cleared up those, but still see these.

Thanks
Aruba

Re: Mobility Access Switches - Error - Flushing port

Since these are connections to other switches you don't actually want to have portfast enabled. Portfast on trunks is meant to be used with end devices like IP phones that don't participate in STP (e.g. BPDUs) so that the port transitions to forwarding as quickly as possible, trunks to other switches on the other hand should go through the STP process to ensure there isn't a loop in the network.

 

So if you are seeing "flushing" a lot, that indicates we are receiving a lot of TCNs or seeing trunk links go up/down. You may want to check the interface stats to see how frequently they have flapped or check the other switches to see whether they have portfast enabled or disabled, if disabled they may be generating the TCNs which we are responding to.

 

Best regards,

 

Madani

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