Access Switches not accessible when stack member got rebooted.

[Siddharam M]

Hi All ,

We have got 2 3750 switches in the stack which are connected to access switches with 2 uplink ports .  each 1 uplink from each physical stack switch .

Due to some power issue our member switch got rebooted. After the reboot the access switches were not reachable through ping , but i was abe to see access switches in "show cdp neighbour" .   Then i rebooted the master switch and member switch one after other . after which i was able to ping the access switches.

Can anyone let me know what might be the issue over here.

IOS Version : c3750-ipservices-mz.122-35.SE5.bin

Thanks in advance....

Regards,

Siddharam

[Giuseppe Larosa]

Hello Siddharam,

without an explicit configuration when the master of the stack changes, the MAC addresses used by the stack changes for STP and also for the SVIs.

if the stack provides the IP default gateway to access switch management what could happen is that for the change the access layer switches had wrong ARP entry for their default gateway.

You can reduce the effects of a change in mastership by using MAC address persistency as described in configuration guide

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_35_se/configuration/guide/swstack.html#wp1206500

The switch stack MAC address is determined by the  MAC address of the stack master. When a stack master is removed from the  stack and a new stack master takes over, the default is for the MAC  address of the new stack master to become the new stack MAC router  address. However, you can enable the persistent MAC address feature

stack-mac persistent timer 0

Hope to help

Giuseppe

[Leo Laohoo]

We have got 2 3750 switches in the stack which are connected to access switches with 2 uplink ports .  each 1 uplink from each physical stack switch .

Ok, looks good.  HOW are the two uplinks configured?  As an EtherChannel?

[Siddharam M]

Hi ,

Yes .... We have bundled those link into an etherchannel ..... after the member reboot the status of port channel & physical ports were up .. but i was unble to learn the mac address.

Regards,

Siddharam