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I've inherited a fairly messy situation with a production network. DHCP is being handed out by a proprietary vendor device, and we need to retire this device as soon as possible.

We'll be moving to pfSense for DHCP (and many other things); however, the DHCP addresses that have been allocated - which have been the same for years - are now "hard-coded" into many applications, and therefore we need to keep the allocations as static as possible. This is obviously a terrible situation, and we're going through the hundreds of devices and moving them to static IPs as quickly as we can. There's no way to export the DHCP table from the old device.

Looking at the spec it suggests that, when a client requests an IP from DHCP, it'll ask for its existing IP from the server.

Therefore, if we switch off the old device and switch on DHCP on pfSense, can we assume that all devices will be reallocated their existing IP from pfSense?

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KenD
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  • I think that depends on the DHCP server settings, if they allow "reallocation" of non-used addresses to clients. I don't know how pfSense DHCP server is configured. – Tero Kilkanen Aug 13 '17 at 16:28
  • i think that as long as you create all the reservations on the new DHCP server and put it on the network (even parallel running with the existing one), it should be ok, you should be able to shutdown the old one, and when a client requests an IP the next time (at the end of the DHCP lease time), it will get the IP from the new device (the same IP as you created the reservations already). but you will have to recreate everything manually.. which might be your problem if you have too many clients – olivierg Aug 13 '17 at 19:26

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You can "extract" the current MAC-to-IP mappings by using ARP (ping them, look at ARP cache). Then, rebuild the same mappings through IP reservations on your new server. Switch over. Done.

Zac67
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