Catalyst 3750 stackwise + Catalyst 3560 Etherchannel problems

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Apr 25th, 2010
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Hi Guys,

in our office we have two 3750 24P in stack that act as core switch and has 10 vlan. We have experience three times a power fault of one of the switch (that was everytime the master), and after the re-election, all the phones connected to Catalyst 3560 (access switch, that are connected to the two core switch with Etherchannel) cannot contact the default gateway that is on the vlan of two core switch. To fix the problem we need to reboot entire stack so the first switch re-become master. I've check the configuration and all two switch has same priority, now i've changed to 5 the priority of the master (switch n°1) and to 1 the priority of the slave (that actually is the master but in normal operation day is slave). The strange problem is that only the phones don't work, every other VLAN works without problems. I've also tried a clear of mac-address table but doesn't work. Tomorrow we have to do another reload of the stack to fix this problem (and accumulate other down of services).

I've seen on the stackwise configuration guide the command "Persistent Mac-address", but this can be used only for 4 minute before change the stack mac-address, can be set to "always" to keep the same mac-address?

We have also reloaded all access switch in the past, but phones still not work. And all the phone that cannot contact the gateway are on the arp table of core switches.

Anyone has an idea how to solve the problem?

Thank you so much.

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Hitesh Vinzoda Fri, 05/14/2010 - 06:35
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What do you mean by other things work and phones doesnt ? Correct me if im wrong,


3560 connected to stack via two different ports in individual switch in stack...

Have you checked your STP convergence time from primary to secondary ? check the STP version and also check the root placement in topology.


Hitesh Vinzoda


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