I encountered a very difficult to troubleshoot problem because
dhclient-script changes /etc/resolv.conf and it was not obvious why it
was happening.

I would like to suggest that dhclient-script include a header at the top
to help the user/admin if the change is unexpected/undesired.  Something
like this would be very helpful:

# automatically generated by dhclient. Any changes will be overwritten.
# See dhclient-script(8) for how to configure/ignore certain options.

Here is the relevant mailing list discussion:

https://lists.debian.org/debian-user/2017/10/msg00779.html

Regards,

Dear submitter,

as the package isc-dhcp has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/1143544

The version of this package that was in Debian prior to this removal
can still be found using https://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Thorsten Alteholz (the ftpmaster behind the curtain)