With 802.1d, when the switch receives a TCN from the root it will drop the mac-address aging time to 15 seconds. The root switch will send PDUs with the TCN flag set for max age +forwarding delay= 35 seconds.
I'm fairly certain it only ages out the mac table entries associated with the STP instance that received the TCN. Using per-vlan spanning tree. If you are using Portfast on the access port, it doesn't generate a TCN. All of this only applies to 802.1d, if you are using 802.1w (RSTP) it uses a different mechanism for topology notification and just flushes the mac table instead of lowering the aging time. Phil On Jul 14, 2007, at 9:41 AM, Kamlesh Sharma wrote: > As stated in the sentence > "The TCN only has an impact on the aging time" > > When there is a TC-N received by the switch. It will change it's > aging time > to 15 sec or max_age + forwarding delay = 35. > > My confusion is : > it will change it's aging time for whole mac forwarding table > or > > Case 1 - TCN recieved on access port for VLAN 20 > age out all mac address learned on that access VLAN 20 > > Case 2 - TCN received on trunk port for VLAN 2 and VLAN 3 > > age out for all mac address learned on the trunk for VLAN 2 and VLAN 3 > > Case 3 - TCN received on trunk port for all allowed VLAN > > age out for whole MAC forwarding table. > > Thanks > > -- > Thanks > Kamlesh Sharma > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
