Hostname differences between servers

Norman Elton normelton at gmail.com
Tue Oct 2 19:13:00 UTC 2018


An update after further research!

In the previous example, e8802ea2eb7f (an Apple device) is requesting
10.45.13.196. One server, landlord02, is erroneously stating that the
client hostname is android-9375f90cad51e32f. It turns out that, a few
days ago, landlord02 offered this IP address to an Android device with
the hostname of android-9375f90cad51e32f. Looking at the source code,
it appears that dhcpd is not reporting the hostname found in the
packet, but rather, the information collected from its lease file.

I suspect this is a corner case, related to the failover mechanism.
But is there a reason it's logging from the lease file and not from
the packet itself? The log message could reasonably be interpreted to
mean that e8802ea2eb7f is reporting an Android hostname.

Thanks!

Norman
On Tue, Oct 2, 2018 at 10:53 AM Norman Elton <normelton at gmail.com> wrote:
>
> In our environment, we have multiple routers (VRRP) forwarding
> requests to two DHCP servers, run in failover. So if a client
> broadcasts out a DHCPREQUEST, that message is handled multiple times.
> Not a big deal, it's been working great for years.
>
> We've just noticed that, sometimes, the hostname reported by the two
> servers don't match each other. For instance:
>
> Oct  1 01:03:48 landlord01: DHCPREQUEST for 10.45.13.196
> (128.239.10.121) from e8802ea2eb7f (Michaels-iPhone) via 10.45.13.2
> Oct  1 01:03:48 landlord02: DHCPREQUEST for 10.45.13.196
> (128.239.10.121) from e8802ea2eb7f (android-9375f90cad51e32f) via
> 10.45.13.2: lease owned by peer
>
> So, is it an android, or is it an iPhone? In this case, the mac
> address points to Apple, but why is one server reporting the hostname
> is android-9375f90cad51e32f?
>
> This is happening fairly frequently. Our servers are running the
> RHEL-provided version of ISC dhcpd, 4.1.1-61.P1.el6_10.
>
> Any ideas?
>
> Thanks,
>
> Norman


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