force DDNS update
dhcp1 at thehobsons.co.uk
Mon Apr 23 22:45:09 UTC 2007
Carl Karsten wrote:
> >> Is there some way to get dhcpd to do this?
>That makes me sad.
Why ? In NORMAL operations, the only time a DNS update is required is
on a dhcp client-server interaction - either giving out a a lease to
a client, or expiring a lease.
> >> This has me wondering:
>>> Box1 does DHCPREQUEST and gets a lease.
>>> Could a Box2 construct a DHCPRELEASE that looks like it came from
>>>Box1 so that
>>> the dhcp server doesn't know that Box1 is still using the IP?
>> Yes, it is almost trivial to do. Just create a DHCP-Release with the
>> other machines MAC address and send it to the server. This might not
>> actually get your too far though, the server will not give it to
>> another client for two reasons :
>> 1) It will not be chosen for reuse until other, less recently used,
>> addresses have been exhausted.
>> 2) It will gte abandoned when the server does a "ping before offer"
>> check - assuming of course that the client doesn't have a firewall
>> blocking pings (which IMHO is a stupid thing to do !)
>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.
>I am not complaining about security issues or suggesting that this
>to be made more robust (if it is a hostel environment, set static IP's and
>static dns.) What I am bitching about is being made to jump though a hoop
>(which generally is what causes me to break things) for the sake of a safety
>feature. Who is this feature keeping safe?
>ok, maybe bitching isn't the right word. Looking for options. especially now
>that I know it isn't just my setup that has this problem.
>What would it take to call a script each time a lease is given?
IIRC, "on commit" !
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