Migrating subnets between failover peers

Simon Hobson dhcp1 at thehobsons.co.uk
Fri Jul 12 19:05:03 UTC 2019

Bob Harold <rharolde at umich.edu> wrote:

> Set as "authoritative" if desired (probably a good idea).

It's far more than "a good idea" - unless you have a good reason to leave it off, then you should always have your server(s) set as authoritative. I have first hand experience of what can happen if a server is not authoritative with certain clients.
Specifically, Microsoft chose to deal with stability by having the clients be very "clingy" to their address rather than doing it in the server. As a result, if you move a Windows client to a different network then it will persist on trying to use it's lease until expiry - while other clients seem to be better at noticing that the network has changed. If the DHCP server is authoritative, then it will Nack requests from the client and thus force it to ask for a new lease and largely avoid this issue - if it's not authoritative then you are far more in the hands of client behaviour.

Worse than a client trying to use an address from a different subnet (and thus stopping that client from working), would be a client trying to use an address from the same subnet (ie RFC1918 address) but from a different network - and thus causing an address collision that could take out more than just the one client.

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