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New Member

How to migrate VLANs

Hello

I've been tasked with "migrating VLAN A to VLAN B" and I'm not sure where to begin. The purpose of this task is to get rid of our old IP addressing scheme for VLAN A, remove VLAN A, create a new VLAN (VLAN B), and assign all devices originally on VLAN A new IP addresses on VLAN B. How do I get this done and where do I begin? Any and all feedback is welcome. Thanks...

3 REPLIES
New Member

Re: How to migrate VLANs

How many devices are on VLANs A & B? How many of those devices are using DHCP?

Are you saying the end result should be the same exact population on the same exact network with different IP Addresses? Is it a matter of taking everyone on the VLAN and migrating them from one IP Address scheme to another.

New Member

Re: How to migrate VLANs

Yes, that's exactly what i'm saying (regarding the end result you outlined above and this being a matter of migrating folks from one IP address scheme, VLAN A, to another, VLAN B.) As for how many devices are on VLAN A, I have no idea! Is there a way to find out via the routers/switches, or do I need to ask around the organization and see who knows of devices on VLAN A? (Same goes for DHCP.) Right now, I do know that VLAN A houses our RAS Dial Up router (a 3640), so that's one device that needs to be migrated.

New Member

Re: How to migrate VLANs

This is quite common. First off, from a OSI perspetive your issue is really at Layer 3 not Layer 2. Currently your old IP subnet is on VLAN A. However you could also implement the new IP subnet on VLAN A since Layer 3 is independant of Layer 2. During the transition, hosts configured for the new IPs will not be able to directly communicate with hosts on the old IPs but this okay. At the router you just configure a secondary IP range on the interface routing for that vlan. This allows you to seemlessly migrate users to the new IPs without changes Layer 2. Once all hosts have been migrated you reconfigure the router with only a statement for the new IP address range.

Or you could create a VLAN B for the new subnet and "bridge" the VLANs together with a cross-over cable. This essentially creates one big bridging domain (regardless of VLAN number). Then you would still create a secondary address on the router interface.

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