Secondary Vlan IP Address for migration to new subnet & DHCP smart relay

[darrenriley5]

Hi,

We have a small subsidury with 3 remote office sites, laptop users can move between each office. The laptops are configured with static ip addresses so to get around the problem of not being able to move between sites we have the same VLAN LAN subnet at each site 10.176.128.0/24 and then NAT the LAN subnet to a different subnet across the VTI tunnels.

Site 1 LAN subnet NATs to 10.200.129.x

Site 2 LAN subnet NATs to 10.200.130.x

Site 3 LAN subnets NAts to 10.81.2.x

What we would like to do is implement DHCP without having to use a big bang approach as its impossible to change all laptops users NIC cards to DHCP at the same time.

My thoughts are to use a secondary IP address on the vlan interface on each of the 3 routers which is advertised into EIGRP and use ip-helper address on the vlan for DHCP to run across the WAN.  After looking into this I will need to use ip dhcp smart-relay command on the routers so to be able to use DHCP with a secondary ip address. Without this command all DHCP requests are forwarded using the primary IP address on the interface so it wouldn't work.

I'm hoping I should be able to use a phased migration approach so static & dhcp can work together for a period of time.

Does this seem reasonable?

Thanks

[Richard Burts]

If you keep 10.176.128.0/24 as the primary address and the new address as secondary then you would need dhcp smart-relay. But let me suggest that you think about making the new address primary and 10.176.128.0/24 as the secondary. This will allow the DHCP to be more simple, will allow the old addresses and address translations to continue to work, and will make the transition easier when everyone is using DHCP and you want to discontinue using 10.176.128.0/24.

HTH

Rick

[darrenriley5]

Hadn't thought of that approach but makes sense. Thanks for your help.

[Richard Burts]

I am glad that you found my suggestion helpful. One of the real advantages of these forums can be having someone suggest a different perspective on an issue that we are working on.

Thanks for the rating.

HTH

Rick

[boulest]

Rick is right on point. the best preactice is to have the new segment on as primary and the old one as secondary