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Today's Topics:
1. Re: ddns-fwd-name using the wrong name (Rob Moser)
2. Re: ddns-fwd-name using the wrong name (Simon Hobson)
3. Re: ddns-fwd-name using the wrong name (Glenn Satchell)
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Message: 1
Date: Thu, 8 Feb 2018 20:15:17 +0000
From: Rob Moser <rob.mo...@nau.edu>
To: "dhcp-users@lists.isc.org" <dhcp-users@lists.isc.org>
Subject: Re: ddns-fwd-name using the wrong name
Message-ID: <4ecc048e218b4ccaa67953370f3cf...@nau.edu>
Content-Type: text/plain; charset="iso-8859-1"
Simon Hobson <dh...@thehobsons.co.uk> wrote:
> Rob Moser <rob.mo...@nau.edu> wrote:
>
> > In most cases our DDNS setup works fine, but an issue has come up where for
> > some of our hosts the DHCP server seems to pick the wrong ddns-fwd-name to
> > send in the updates to DNS. How does dhcpd determine what name to use?
> ...
> > Any ideas where dhcpd might be getting this old out-of-date value for
> > ddns-fwd-name? Thanks for any help,
>
> My guess is that it's persisting with the one in the leases file rather than
> re-evaluating the value every time it deals with the client.
> Simple test for that is to configure a client, change it's hostname, see if
> it does the same - then stop the DHCP server and delete the
> ddns-forward-hostname entry in it's lease (only the last entry in the file
> matters) before restarting the DHCP server.
I think you're right, and I think I know why.
As often seems to be the case, the act of writing my problem up sparked another
few ideas for me to try. Because I came at this from an original DNS problem,
I was focussed on the name, but since I've now worked out the name is coming
from DHCP, I really should be tracking things by MAC address...
Sure enough, there is another entry in my dhcp.leases file for the MAC in
question, and it looks like:
host MATH222-20.math.our.domain-dynamic {
dynamic;
hardware ethernet 18:03:73:41:33:5b;
supersede server.ddns-hostname = "MATH222-20";
supersede server.ddns-domainname = "math.our.domain";
supersede host-name = "";
supersede domain-name = "math.our.domain";
}
So clearly _that_ is where the obsolete name comes from. But that just kicks
the can down the road a ways; where did that entry in my leases file come from,
if there are no equivalent entries in my dhcpd.conf files? Could the old value
still be coming from the client somehow? (The only definition I could find for
the "supersede" clause was in the dhclient.conf man pages....) Or have come
from the client back when it legitimately had the old name, and is not getting
overwritten by the new one for some reason? I grabbed a tcpdump of traffic
from the system during a renew, and I can't see any sign of the hostname (but I
wasn't able to force a release first, so it wasn't a full discover-cycle.)
Thanks for the help,
- rob.
------------------------------
Message: 2
Date: Thu, 8 Feb 2018 20:31:55 +0000
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: ddns-fwd-name using the wrong name
Message-ID: <d70f4fff-158b-4d26-9bfe-674167eb3...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii
Rob Moser <rob.mo...@nau.edu> wrote:
> But that just kicks the can down the road a ways; where did that entry in my
> leases file come from, if there are no equivalent entries in my dhcpd.conf
> files?
Does one have a client-id and the other not have one ? If so, then they would
be considered different clients (did they get different addresses) and the old
lease could stay around for a long time. But then the DHCP server should not be
applying that lease to the host in question.
But then, that lease entry doesn't look like anything I've seen, so rather a
case of "I dunno" - sorry.
------------------------------
Message: 3
Date: Fri, 9 Feb 2018 17:39:20 +1100
From: "Glenn Satchell" <glenn.satch...@uniq.com.au>
To: "Users of ISC DHCP" <dhcp-users@lists.isc.org>
Subject: Re: ddns-fwd-name using the wrong name
Message-ID:
<67acc015f031083d4e4d0f3c008d78ed.squir...@mail.uniq.com.au>
Content-Type: text/plain;charset=iso-8859-1
On Fri, February 9, 2018 7:31 am, Simon Hobson wrote:
> Rob Moser <rob.mo...@nau.edu> wrote:
>
>> But that just kicks the can down the road a ways; where did that entry
>> in my leases file come from, if there are no equivalent entries in my
>> dhcpd.conf files?
>
> Does one have a client-id and the other not have one ? If so, then they
> would be considered different clients (did they get different addresses)
> and the old lease could stay around for a long time. But then the DHCP
> server should not be applying that lease to the host in question.
>
> But then, that lease entry doesn't look like anything I've seen, so rather
> a case of "I dunno" - sorry.
>
The "dynamic;" entry marks it as something added using OMAPI, ie by
omshell. Is is possible that this was done sometime in the past?
regards,
-glenn
------------------------------
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