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It turns out the two random open ports are related to the dynamic DNS
feature (NSUPDATE).

I modified the source code as per instructions at (
http://forums.debian.net/viewtopic.php?f=10&t=95273) (forums.debian.net,
dhclient UDP ports, 2013-02-01), recompiled, and reran with the random
ports disappearing.


Bug Report:  Add into the documentation for dhclient that it has the
NSUPDATE functionality which causes it to listen on the IPv4 and IPv6
ANY_ADDR interface on random UDP ports.

Additionally their should be a run-time configuration option that enables
that behavior with it disabled by default.  A recompile should not be
required to disable the ports.


On Thu, May 2, 2013 at 4:57 PM, Rodney D Beede via RT <dhcp-bugs@isc.org>wrote:

> Also seen on Debian.
>
> http://forums.debian.net/viewtopic.php?f=10&t=95273
>
>
>
> -------------------------------------------------------------------------
> > When I run dhclient it listens on the expected port 68.  However, in
> > addition to that port it also listens on a high number random IPv4 port
> and
> > IPv6 port (even if I specify -4 as an option).
> >
> > Reading through the source code would make me think this is related to
> > OMAPI somehow?
> >
> > I tried this on Ubuntu Server 13.04 64-bit which came with dhclient
> version
> > 4.2.4.  I also downloaded, compiled, and tried the latest version
> > isc-dhclient-4.2.5-P1.  I get the same result.
> >
> > I believe this is a bug.  Either it shouldn't be listening on these ports
> > or it should be documented what they are used for.
> >
> > Screenshots attached.[image: Inline image 1]
> >
> > [image: Inline image 2]
> >
> >
>
>