Mismatched VSS Configs

[marc.russo]

I built a VSS pair with a couple of 6509's.  This was our first pair so we took the opportunity to do some testing.  One of the features we tested was the priority/preemption feature, which we decided not to use.  After some time we shutdown switch 1 and relocated it to another building.  Unfortunately, because of a lack of fiber, it was not connected to switch 2 for several months.  Also, unfortunately, I failed to remove the priority commands.  Now while switch 1 was "unconnected", we made changes to the config on switch 2.  Months later, when the fiber was complete and I connected switch 1, preemption caused it to take over.  I'm guessing switch 1 thought it's config file was the better one, and proceeded to overwrite switch 2's production config.  I quickly disconnected the fiber but not before losing my production config on switch 2.  We of course recovered from that with a backup, but now I need to connect switch 1 again.  I have removed the priority command from switch 1 and rebooted it.  The "show switch virtual role" show an oper(conf) priority of 100(100) on switch 1.  Switch 2 also shows 100(100).  The config on switch 2 (the running prod switch) shows this:

switch virtual domain 100

switch mode virtual

switch 1 priority 110

mac-address use-virtual

I'm guessing I need to remove the "switch 1 priority 110" command from here as well.  My real question is, when I reconnect switch 1, with the priority commands removed, will my production config on switch 2 be preserved and written over to switch 1?  How do the two switches decide which config to use if the two are different?

[Mohamed Sobair]

This should not happen. There is no config Mismatch in VSS terminology.

The Virtual-Switching system allows both hardware to operate as one logical switch, at the same time ONLY Asingle  Supervisor Engine is activated on a time, however, both SUPs should be in Synch and Have identical Configuration at both ends.

with the priority command, you decide which SUP you want to be active and which one is backup, but that doesnt mean both SUPs have different config. I assume there is something else rong happend in your Netork which erased the Config.

Regards,

Mohamed

[marc.russo]

The problem is that because the two switches were disconnected from each other, both SUP's were active.  They had different configs because we were configuring switch 2, but never switch 1.  When they were finally connected, switch 1 had a better priority, but an out of date config.  I assume that because switch 1's priority was better, it pushed it's config to switch 2.

[Mohamed Sobair]

I see now.

In this case the symtoms you are observing and talking about is correct. I originally though they were already Connected VSS and working fine , that why I was confused.

However, if they were disconnected with different Config, the Switch with the higher priority wins, and the Active SUP engine synchs its new config to the Secondary Switch Supervisor Engine. This is normally performed by VSS pairs to maintain identical Config.

Regards,

Mohamed

[marc.russo]

So, back to my original question.  If the priorities are now the same, and I connect the two switches, which config will take over.  Should I copy the config to swith 1 before I connect them?

[Mohamed Sobair]

By default, the Switch configured with (Switch 1) will assume the Active role, and the Switch configured with (Switch 2) command will assume the Standby role.

You just need to make sure (Switch 1) has the current and desired config.

Of course, its always better to have a backup config on hand incase of any problem or disaster similar to the one you have gone through.

Regards,

Mohamed

[Reza Sharifi]

What ever config you have in switch-1 will sync with switch-2.  So, you only need to configure switch-1 (primary). As a matter of fact, if VSS is working correctly, you don't even have access to switch-2 (stand-by).  Also, you do not need to configure priority.  Switch-1 will always be the primary until there is a failure. Configuring priority can cause the switches to reboot and also confuse the admin staff to figure out which switch is the primary and which is the stand-by.

HTH

[marc.russo]

Just to let everyone know what the resolution was...I set the priority to be the same on both switches.  I then copied the current config from switch 2 (the prod switch) onto switch 1.  I rebooted switch 1 and while it was booting up, I connected the VSL link.  Once switch 1 completed it's bootup sequence, the VSL came up and all was well.