WS-C3650-48TS Stack Fail-over

[Dan McGuire]

Hello,

I'm wondering if someone could please help me understand the layer 2 fail-over time for switches running in a stacked configuration.

Switch Model: WS-C3650-48TS 

Software version: 03.06.04.E

Software Image: cat3k_caa-universalk9

Scenario:

I have two Cisco C3650 switches running in a stacked configuration and am seeing some ping loss when doing fail-overs.

My setup is pretty simple for the test.

1. Laptop is plugged into a vlan 52 access port on the switch that is not currently the master

2. Laptop is running a continuous ping to the vlan 52 SVI IP. Wireshark is also running to get a better sense of time.

3. Power gets pulled on the master

4. Ping loss occurs for about 5 seconds

5 seconds isn't terrible but I was really expecting something much quicker such as 2 seconds or less due to the switches being stacked. Am I expecting too much?

My suspicion is that the SVI is slow to send a gratuitous ARP out for the new master thus not updating hosts on vlan 52 but I'm not 100% sure.

Can someone possibly enlighten me on what's going on? Any help would be greatly appreciated. 

Thanks,

Jim

[Reza Sharifi]

Hi,

So, 5 seconds is not too bad because when you unplug the power from the master, there is going to be an election, so the member can become the master.  Do you see the same amount of delay if you unplug the power from the member switch?

HTH

[Dan McGuire]

Thanks for the reply Reza.

From what I remember, if I pull the power on the switch that is not the master, the fail over is quicker but I will have to give it a try tomorrow and will let you know the results.

Thanks!

[Leo Laohoo]

I'm going to agree with Reza.
<7 seconds for a failover is not bad for a stack of 3850.
A lot of factors will come into play whether it is 2 or 5 seconds, such as:
1. IOS version;
2. Configuration and complexity;
3. IPv4 or IPv6;
4. Multicast
And more.