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3750 Stack Switch Issue


I have Stack of 7 3750 Switches. In that Switch 1 is master with 15 Priority and other switches are Member but because of some reason switch 1 rebooted and then Switch 2 becomes Master because it’s having 14 Priority.

We have 2 uplinks which connected on switch 1 (1/1/1) and switch 6 (6/1/1) Tengig port. Also we have 4 AP connected on switch 6.

So we observed that the Switch 1 came up and after that 3 AP is disconnected from WLC. if we disconnect the uplink port on Switch 1 (1/1/1) AP will connect the WLC and using uplink 6/1/1 but if we connect uplink port 1/1/1 and disconnect the uplink port 6/1/1 all 4 AP will disconnect from Network.

We try to connect the Uplink 1/1/1 to Switch 1 other port 1/1/2 but face the same issue. So we reconnect the port 6/1/1 and used the same link which connect on 1/1/1 to switch 7 (7/1/1) and AP will connect on WLC. So as per this troubleshooting we thought some issue with Network Module or Switch of Switch1.

So we Swap the Network module between Switch1 and Switch7 and connect the uplink on 1/1/1 but face the same issue and if we connect the same uplink on Switch 7 Ap connect to WLC.

So we thought that Switch is having issue. But before raising an RMA for Switch we observer 1 more thing that. Earlier that when the Switch 1 is Master all 4 AP's connected to WLC and working fine but when the Switch1 became rebooted and Switch2 became Master issue started. So we rebooted the Switch 2 and make switch master and found that while connecting on port 1/1/1 of Switch port AP's are able to connect to WLC and Issue resolved.

So I wants to know that is there any requirement that If the high priority switch rebooted and after came up it should not be Master then connected uplink will not work.

Also let us know what’s happen if the high priority switch came up in network. Means it’s will became Master or Menber.


Just now i Found one bug which is matching on our issue.

3750x stack fails to update ARP table after reboot causing traffic loss

BUG ID:-CSCtz98066

Symptoms: When the master switch (Switch A) is reloaded or loses power and

rejoins the stack as a member switch, any traffic stream being sent through

Switch A is unable to be received by the destination because the newly joined

member is not able to establish an ARP entry for the next hop router/switch.

Debugs confirm that Switch A does not send a GARP/ARP for the next hop, though

traffic continues to be sent to the switch.

Conditions: The symptom is observed when only Switch A has a physical

connection between the source and destination router/L3 switch. The newly

elected master (Switch B) does not.

Workaround: Ping destination from Switch A, forcing ARP request/response.

Also affected version is 12.2(58)SE and15.0(1)SE2 and we are using IOS 12.2(58)SE.

So we are going to upgrade the devices by this weekend with IOS 15.0(2)SE5.

Will update you once we upgraded the switches.

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