Multiple DHCP Servers with DDNS Best Practice/Workaround?

Simon Hobson dhcp1 at
Thu May 12 15:30:24 UTC 2011

Colin Simpson wrote:

>  > With separate dhcp servers it really needs some inter-server
>>  communication to release the old lease and remove the DNS entries. The
>>  ISC server doesn't have that facility.
>Not sure they'd need to communicate if you could arrange for some method
>of consistently generating the TXT entries across servers.

Yes you would. Take this simple timeline :
Server A issues lease and adds DNS entries
Client move to another network
Server B issues lease and updates DNS
Lease at server A expires, server A removes DNS entries.

Client now has no DNS entries, and Server B will not add them again 
as it's lease record shows that it's already added them. Client will 
be without DNS entries until it either moves to another network (so 
Server C can add them), or it's lease expires with server B and it 
then rejoins the network. In the former case the client will get DNS 
entries, but only until it's lease at server B expires and they get 
removed again.

To avoid this you would either need to prevent deletion of the DNS 
entries (in which case you'd need to come up with some means of 
garbage collection), or modify the code to not delete entries if the 
A record doesn't match what the server thinks it added. The latter 
would probably work, but it's more code hacking.

Simon Hobson

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