Core Layer Hardware Change

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May 1st, 2008
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We currently run 2 3550's using HSRP as our core switches. They also control all intervlan routing. We have about 20 connections coming into these switches from our various wiring closets. I want to upgrade these two switches to a stack of 3750's utilizing StackWise technology. How would I go about this to disrupt my network the least? Should I give the 3750 stack a different IP address from the 3550's, enable RIP to sync the routing tables, and then shutdown the VLAN interfaces on the 3550 and create the VLAN interfaces on the 3750 stack using the same VLAN interface IP address? This would allow me to maintain my routing with only a short disruption to each VLAN while I shut it down and "move" it to the 3750 stack. Once all VLANS have been moved, I should then be able to disconnect the incoming fiber from the 3550, connect the fiber to the 3750 stack, and finally shut down the core 3550 switches. Does this sound like a viable solution or is there a more simple route?


Thanks in advance for any help,


Ken

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Joseph W. Doherty Thu, 05/01/2008 - 17:47
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Perhaps what might be done, insure one 3550 is the active HSRP gateway for all subnets, then replace standby 3550 with 3750 configured like it. Make the 3750 stack active HSRP gateway for all subnets. Remove the remaining 3550 and connect its ports to the 3750 stack.


Note, the second set of port relocations will likely require further reconfigurations since you'll have one less core router. For instance, Etherchannel the dual connections from you access switches to different 3750 stack members (BTW: configure channels while replacing first 3550).


Also note, as you remove replace switches, depending on your topology, you might have STP convergence (although not much different from if you physically lost a 3550).

Istvan_Rabai Thu, 05/01/2008 - 17:56
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Hi Ken,


I probably would do the following:


1. In the lab, I would create the same layer2 and layer3 configs in the 3750 stack as you have in the 3550s, including vlans, trunks, ip addresses, routing, HSRP etc.


2. I would test, still in the lab, that the 3750 configs work properly.


3. During an off-work hour I would change the switches.


4. I would test all the connections using the new 3750 switches.


Cheers:

Istvan


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