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Today's Topics:
1. Debian Buster dhclient v6 overwrites resolv.conf with prepend
domain_name_servers (d...@biblestuph.com)
2. Re: Debian Buster dhclient v6 overwrites resolv.conf with
prepend domain_name_servers (Rudy Zijlstra)
----------------------------------------------------------------------
Message: 1
Date: Sat, 18 Sep 2021 14:44:40 -0400
From: d...@biblestuph.com
To: dhcp-users@lists.isc.org
Subject: Debian Buster dhclient v6 overwrites resolv.conf with prepend
domain_name_servers
Message-ID: <1cba524d-8e5e-4475-1eb5-ec10db105...@biblestuph.com>
Content-Type: text/plain; charset=utf-8; format=flowed
My Debian Buster AWS instance runs two copies of dhclient
(isc-dhclient-4.4.1), one for -4 and one for -6. I wanted to prepend my
localhost 127.0.0.1 to the nameservers written to resolv.conf, so I
uncommented this line in dhclient.conf:
prepend domain-name-servers 127.0.0.1;
but instead of prepending, on the first execution after boot I get
_only_ the localhost in the resolv.conf, nothing else. It's not the
worse thing in the world as the next RENEW rewrites it with the fully
correct values, but it's missing some intended values until then. (And
later RENEW6 calls won't update, see the logic snippet below.)
Troubleshooting I found that on boot the v6 instance was overwriting the
resolv.conf written by the v4 instance; I.E., the v4 dhclient-script
instance gets (verified by the debug hook) BOUND, new_domain_name, and
new_domain_name_servers, the last with my 127.0.0.1 in front as I
expect, and therefore writes the resolv.conf as expected. But then it is
immediately followed by a BOUND6 call from the v6 instance, which _also_
gets new_domain_name_servers but with _only_ the localhost entry and no
new_domain_name. As a result, this logic in dhclient-script gets tripped:
# update /etc/resolv.conf
if [ "${reason}" = BOUND6 ] ||
[ "${new_dhcp6_name_servers}" != "${old_dhcp6_name_servers}"
] ||
[ "${new_dhcp6_domain_search}" !=
"${old_dhcp6_domain_search}" ]; then
make_resolv_conf
fi
and make_resolv_conf rewrites per this logic:
# DHCPv4
if [ -n "$new_domain_search" ] || [ -n "$new_domain_name" ] ||
[ -n "$new_domain_name_servers" ]; then
So ... is this a known issue, and/or is there a graceful work around?
Thank you!
Dan
------------------------------
Message: 2
Date: Sat, 18 Sep 2021 21:43:48 +0200
From: Rudy Zijlstra <r...@grumpydevil.homelinux.org>
To: dhcp-users@lists.isc.org
Subject: Re: Debian Buster dhclient v6 overwrites resolv.conf with
prepend domain_name_servers
Message-ID:
<c4ae8b33-6f4e-b4cd-dbfe-638cbbec8...@grumpydevil.homelinux.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi
On 18-09-2021 20:44, d...@biblestuph.com wrote:
> My Debian Buster AWS instance runs two copies of dhclient
> (isc-dhclient-4.4.1), one for -4 and one for -6. I wanted to prepend
> my localhost 127.0.0.1 to the nameservers written to resolv.conf, so I
> uncommented this line in dhclient.conf:
>
> prepend domain-name-servers 127.0.0.1;
I would suggest to run the two instances with each their own config
file. In the v6 version do not use the prepend statement
Cheers
Rudy
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