changing root bridges... any affects on network performance?

[banajahm]

hi,

my switching background is a bit shakey. i have 2 simple questions for you guys:

1) i have a cat2950 that is configured as the root of STP. it is also the VTP server. i want to make some changes so that our 4500 is the VTP server and ST root. this will be done on a mission critical segment of our network. should i expect any network degridation in the first 60 seconds of that change? if so, what would be the best way to go about this change with minimul network disruption?

2) in a vtp domain, would it be wise to have more than one VTP server so that each will be the others backup incase of failure? most documents advise having one server and the rest should be clients or transparent switches.

thanks in advance.

[Kevin Dorrell]

1. Yes you will experience network disruption as the root changes. In theory this will last for about 50 seconds in a stably designed network. Anounce the interruption in advance, and do it during maintenance time.

2. Personally, I have two VTP servers on my two distribution layer switches, and keep the access switches as VTP clients. That said, if a lone VTP server fails it should not cause any immediate problem; only if you want to change the VLAN list later. And to get back control of the VTP domain you would have to promote one of the clients to server mode. I would go for two servers.

Kevin Dorrell

Luxembourg

[aashish.c]

Hi,

1) As the STP root will change there will be topology change BPDUs wil fow in the network due to which MAC address tables will age out in 15 seconds. and disruption can be there.

To avoid it to some extent you can configure "Uplinkfast" on some switches which have redundant links to core switch. wherever you apply uplinkfast, that switch will never become root switch.

I would also suggest you to enable "backbonefast" on all switches that will also improve convergence time in the network.

here is a good document which will introduce different STP features to avoid high convergence time :

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950scg/swstpopt.htm

2) You can have more than 1 VTP server because they will all provide redundancy without causing any loop or disruption with each other. if 1 dies the other are there to take care of VTP requests/advertisements. there will be no problem at all.

Regards

aashish C

[banajahm]

thanks guys. now that i know the answer, i can shcedule it into my next maintenance plan.

cheers