Core replacement...phased or knife-edge?

[1gtopf]

I am in the process of getting ready to replace my current overworked stack of 3750g switches with a 4507R+E with a pair of Sup 7-Es.  Nice little upgrade.

Anyway, my current core has all of my servers, routers, etc terminating in it.

I want to know if I can gradually migrate things over to the new switch, and then, when I'm ready to decomission the old one, just re-address the VLANS on the new switch to match what the old one has? 

I've already got the new switch on the network and connected via a trunk to the old one, so network-wise I've got connectivity. I just wasnt sure if it was going to cause any problems changing an IP address on a switch like that.

Thoughts?

[Jon Marshall]

You could actually simply run VTP server/client between the 3750 stack and the 4500 switch. Then you could run HSRP between the 3750 stack and the 4500 switch.

That way you can simply migrate devices into the same vlans on the new 4500 switch and it should all work. When you are ready to decommission the 3750s simply turn them off and the HSRP active gateway then moves to the 4500.

Jon

[1gtopf]

I've already got VTP working, I would just need to change the new switch from client mode to server mode.

HSRP may be a bit compliated (it's beyond my LAN abilities) so would it work without?

[Jon Marshall]

Yes it would work, as long as the 4500 has the same vlans and the connection to the 3750s is a trunk you can simply migrate devices across and allocate them into the same vlan on the 4500 switch.

But then you would need some downtime when you finally had migrated across all devices because you then need to move the L3 vlan interface IP addresses across. This is what i am assuming you were proposing to do.

If you are happy with a bit of downtime then that is all you need to do. If you didn't want downtime then HSRP would allow you to transition seamlessly. HSRP is very easy to setup but it does depend on -

1) existing 3750 config

2) having a couple of spare IPs per subnet

Jon

[1gtopf]

Yes, that was my plan.  I figure I can do a few servers a day, but when it's time to pull down the old stack, some downtime to relocate the final equipment and re-address.