Hi all,
we utilize some 3560-X as well as older 3560-switches for client pc access. Client ports are set with spanning-tree portfast / bpduguard.
The switches uplink through their Gi1/x-interfaces to 2 650x switches that use rpvst+ / hsrp for redundancy. In most cases VLANs are small, covering only one access switch and the core switches.
Funnily the switches seem to see reason to (repeatedly) flush the mac address table entries from the uplink interfaces from time to time.
This means that for all the VLANs on the uplink port the switch needs to relearn these unicast addresses, therewhile flooding the unicasts to all ports.
This happens roughly all 5-20 minutes and repeats between 1 and 80(!!!) times, then about once a second.
Browsing the Internet I found 3 "sane" reasons why mac addresses are flushed from the table
- normal aging -- we tried between 300 and 21600 seconds without any influence.
- spanning tree topology change -- there is none. show spanning-tree vlan <xx> detail doesn't show actual topology changes for *all* vlans.
- someone calling clear mac address-table
Doing a "debug matm bulkdelete" on a 3560-X IOS15.0(2)SE4 we see that the switch calls
mat_delete_all_addrs: mat_instance:0 table_type:1 addr_type:2049, port:0x<varying hex number>
at these times (like I said, repeatedly). Unfortunately we can't identify who or what calls this function...
Can anyone point me to other reasons why the switch should flush the mac address table from these interfaces?
Best regards and thank you!
Stefan
