Re: [gentoo-user] Wireless DHCP takes over resolv.conf

[Fernando Rodriguez <cyklonite@gmail.com>]

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On 07/09/2016 03:25 PM, Mick wrote:
> On Saturday 09 Jul 2016 11:34:59 Fernando Rodriguez wrote:
>> On 07/09/2016 10:53 AM, Mick wrote:
>>> Hi All,
>>>
>>> I just noticed my resolv.conf is topped up with the nameservers of the
>>> wireless LAN I happen to be associated at the time and my wired ethernet
>>> nameserver(s) are pushed further down.  This happens despite the fact that
>>> I have configured my wired ethernet to have a lesser priority than the
>>> wired NIC.
>>>
>>> For example:
>>>
>>> less /etc/resolv.conf
>>> # Generated by dhcpcd from wlan0.dhcp, enp11s0.dhcp
>>> # /etc/resolv.conf.head can replace this lineL
>>> domain openwifi
>>> nameserver 192.168.22.22
>>> nameserver 192.168.22.23
>>> nameserver 10.10.10.254
>>> # /etc/resolv.conf.tail can replace this line
>>>
>>> The first 3 non-commented entries were produced by wlan0, demoting my
>>> wired
>>> ethernet nameserver.
>>>
>>> ip route show
>>> default via 10.10.10.254 dev enp11s0  metric 10
>>> default via 10.160.95.1 dev wlan0  metric 20
>>> 10.10.10.0/24 dev enp11s0  proto kernel  scope link  src 10.10.10.7 
>>> metric 10 10.160.95.0/29 dev wlan0  proto kernel  scope link  src
>>> 10.160.95.2  metric 20 127.0.0.0/8 dev lo  scope host
>>>
>>> If I am associated, but not authenticated with the wireless LAN, any URLs
>>> I
>>> try to visit will be queried with the 192.168.22.2* nameserver, before it
>>> times out and 10.10.10.254 takes over.
>>>
>>> Waiting for URLs to resolve becomes tedious after a while.  Is there a way
>>> to prioritise nameservers so that the NIC metric is respected, whenever
>>> the resolv.conf content is updated?
>>
>> Look at the -C option on dhcpcd's man page. It is done by a dhcpcd hook that
>> you can disable with that option. Where to specify it depends on what
>> you're using to manage your network connections.
> 
> Thanks, that'll work, but it is a nuclear option because, as I understand it, 
> it will work all the time.  So when the ethernet cable is disconnected the 
> wireless will not be able to obtain nameservers.

Check out net-dns/openresolv [1]. I've never used it but it's mean to solve that problem.
If you use NetworkManager I think all you need to do is enable that use flag.

[1] http://roy.marples.name/projects/openresolv/index

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