force DDNS update

[Simon Hobson]

Carl Karsten wrote:

>  >> But that will cause dhcp to remove an A record and allow the 
>dhcp request that
>>>  you describe: someone could name their client "server"...
>>
>>  Except that very few people use dynamic DNS updates to put their
>>  important services into DNS - except Windows of course which seems to
>>  live off DNS updates !
>>
>>  Even if you give servers their address by DHCP, it would normally be
>>  a fixed address which by default would not trigger DDNS - hence
>>  manually adding teh DNS records.

>So even more reason to add an option that turns off the "safety feature"

No, the point is that normally you would put fixed records into DNS 
for your servers - and DHCP will NOT replace these. If your user set 
their client name to "server" then the DDNS update would fail because 
there would NOT be the correct key (TXT record) to go with the 
existing A record.

The client could only take over DNS records for a client with 
Dynamically set DNS records - as you've figured, fake a release 
packet from the other device, set your client name to be the same as 
the other device, go get a lease.

If you are really clever AND the other device doesn't respond to 
pings, request the address you've just has released and take the 
other device offline completely. If the other device does reply to 
pings, I think you can do two discovers, one results in the address 
being abandoned, the second will get it issued to you I think (just 
going from something that came up recently).