04-19-2012 06:31 AM - edited 03-07-2019 06:13 AM
We have a stack of a 3750E with a 3750X, when we turn off the master, a disconnection occurs for around one minute while only one request timeout is seen when the slave is turned off. Is this normal?
Details: in other words, when the slave switch is elected as the new master all the port-channels and some physical ports become in 'down' state before reobtaining the up state again, this results in a one minute outage. The question is: is it normal to have a layer2 control traffic interruption when the master fails and re-election occurs and if yes, what is the normal downtime in seconds. the layer2 control information such as port-channels LACP protocol are not synchronised to all slave switches by the master?
04-19-2012 06:46 AM
One minute between failure is too long. Here are some numbers from Cisco's documentation:
On stack master failure, another switch in the stack takes over
1:N master redundancy
Reconvergence times tested under heavy load:
Layer 1 failure is detected in several microseconds
Layer 2 failure ~ mseconds
Layer 3 link failure—sub 200 mseconds
Layer 3 member failure—sub 300 mseconds
Layer 3 master failure—up to eight seconds
HTH
04-19-2012 07:24 AM
Hi Reza,
Layer 2 failure ~ mseconds is when the master switch fails?
BR
04-19-2012 08:45 AM
Correct. This is when the master fails.
04-19-2012 09:46 AM
ok, do you think that 'stack-mac persistent timer 0' command which is still not implemented will help in decreasing the downtime from 1 minute to mseconds or it will just decrease the time needed to reach the management IP again?
04-19-2012 03:26 PM
I know enabling it defiantly helps when the devices are running layer-3 routing protocols like OSPF
I know your devices are layer-2, but I would try anyway
please keep us posted on the results.
HTH
04-19-2012 10:47 PM
i think it should help also for layer2, this is what i found in my research :
With LACP, the system-id uses the stack MAC address from the stack master, and if the stack master changes, the LACP system-id can change. If the LACP system-id changes, the entire EtherChannel will flap, and there will be an STP reconvergence. Taken from the following reference:
I will update u after doing the test
many thanks
04-30-2012 12:39 AM
test done and what was mentioned in the previous post resolved the problem
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