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

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

[Mick]

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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 line
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?

-- 
Regards,
Mick

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

[Fernando Rodriguez]

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Hash: SHA256

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

[Mick]

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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.

-- 
Regards,
Mick

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

[Fernando Rodriguez]

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Hash: SHA256

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

[Emanuele Rusconi]

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Wouldn't it be better to just use the same servers for both wired and
wireless? It's what I use and it works flawlessly.
In that case you have at least a couple of options:

The second line says:

    # /etc/resolv.conf.head can replace this line

So, you can just put your preferred servers in the /etc/resolv.conf.head
file and they will be written at the top of /etc/resolv.conf .


Or, you can write your own /etc/resolv.conf and add this line to your
/etc/dhcpcd.conf :

    nohook resolv.conf

This is the same as the -C option, and tells dhcpcd to not overwrite
/etc/resolv.conf .



-- Emanuele Rusconi

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

[Alan McKinnon]

On 11/07/2016 10:32, Emanuele Rusconi wrote:
> Wouldn't it be better to just use the same servers for both wired and
> wireless? It's what I use and it works flawlessly.

It works flawlessly *for you*, but by no means can you consider it
correct or stable.

There is no guarantee that a wired and wireless network will use the
same dns caches.

If it happens to work, great, use it. But be aware there will come a day
when that is no longer true.




-- 
Alan McKinnon
alan.mckinnon@gmail.com

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

[Mick]

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On Monday 11 Jul 2016 17:31:29 Alan McKinnon wrote:
> On 11/07/2016 10:32, Emanuele Rusconi wrote:
> > Wouldn't it be better to just use the same servers for both wired and
> > wireless? It's what I use and it works flawlessly.
> 
> It works flawlessly *for you*, but by no means can you consider it
> correct or stable.
> 
> There is no guarantee that a wired and wireless network will use the
> same dns caches.

Yep, furthermore this is a laptop which is taken around the place and plugged 
in and out of wired and wireless networks.


> If it happens to work, great, use it. But be aware there will come a day
> when that is no longer true.

When I get a minute I'll have a look at net-dns/openresolv which Fernando 
suggested.  I think it will do what want.

-- 
Regards,
Mick

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

[Alan McKinnon]

On 11/07/2016 20:13, Mick wrote:
> On Monday 11 Jul 2016 17:31:29 Alan McKinnon wrote:
>> On 11/07/2016 10:32, Emanuele Rusconi wrote:
>>> Wouldn't it be better to just use the same servers for both wired and
>>> wireless? It's what I use and it works flawlessly.
>>
>> It works flawlessly *for you*, but by no means can you consider it
>> correct or stable.
>>
>> There is no guarantee that a wired and wireless network will use the
>> same dns caches.
>
> Yep, furthermore this is a laptop which is taken around the place and plugged
> in and out of wired and wireless networks.
>
>
>> If it happens to work, great, use it. But be aware there will come a day
>> when that is no longer true.
>
> When I get a minute I'll have a look at net-dns/openresolv which Fernando
> suggested.  I think it will do what want.
>

why don't you go with the dns server addresses supplied by each 
network's dhcp? Presumably the admin put them their because they work on 
that network.

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

[Grant Edwards]

On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:

> why don't you go with the dns server addresses supplied by each
> network's dhcp? Presumably the admin put them their because they
> work on that network.

One might think that, but I find it often not to be the case.  I can
recall many networks where the DNS servers returned by the DHCP server
didn't work well at all, and things got a _lot_ better when I manually
configured a couple working DNS servers (e.g. the Google ones at
8.8.8.8 and 8.8.4.4).  Around here, Comcast's DNS servers are famously
bad.

-- 
Grant Edwards               grant.b.edwards        Yow! Hey, waiter!  I want
                                  at               a NEW SHIRT and a PONY TAIL
                              gmail.com            with lemon sauce!

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

[Alan McKinnon]

On 11/07/2016 22:29, Grant Edwards wrote:
> On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>
>> why don't you go with the dns server addresses supplied by each
>> network's dhcp? Presumably the admin put them their because they
>> work on that network.
>
> One might think that, but I find it often not to be the case.  I can
> recall many networks where the DNS servers returned by the DHCP server
> didn't work well at all, and things got a _lot_ better when I manually
> configured a couple working DNS servers (e.g. the Google ones at
> 8.8.8.8 and 8.8.4.4).  Around here, Comcast's DNS servers are famously
> bad.
>

Then shoot the idiot running that wireless network. If he's one of my 
juniors, tell me so I can fire him (as he's just proved he can't do the 
job he's paid to do)

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

[Grant Edwards]

On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
> On 11/07/2016 22:29, Grant Edwards wrote:
>> On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>>
>>> why don't you go with the dns server addresses supplied by each
>>> network's dhcp? Presumably the admin put them their because they
>>> work on that network.
>>
>> One might think that, but I find it often not to be the case.  I can
>> recall many networks where the DNS servers returned by the DHCP server
>> didn't work well at all, and things got a _lot_ better when I manually
>> configured a couple working DNS servers (e.g. the Google ones at
>> 8.8.8.8 and 8.8.4.4).  Around here, Comcast's DNS servers are famously
>> bad.

> Then shoot the idiot running that wireless network.

You're not actually allowed to do that General Dreedle...

> If he's one of my juniors, tell me so I can fire him (as he's just
> proved he can't do the job he's paid to do)

And if you're at a customer or vendor site?  A friend's or relative's
house?  Using a municiple WiFi system?  Using WiFi on an airplane,
bus, train, whatever?

Sometimes you just need to get along with people and get some work
done.  You always can't demand that things get done your way or
somebody's gonna get fired or taken out back and beaten...

-- 
Grant Edwards               grant.b.edwards        Yow! ... I think I'd
                                  at               better go back to my DESK
                              gmail.com            and toy with a few common
                                                   MISAPPREHENSIONS ...

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

[Alan McKinnon]

On 11/07/2016 23:03, Grant Edwards wrote:
> On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>> On 11/07/2016 22:29, Grant Edwards wrote:
>>> On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
>>>
>>>> why don't you go with the dns server addresses supplied by each
>>>> network's dhcp? Presumably the admin put them their because they
>>>> work on that network.
>>>
>>> One might think that, but I find it often not to be the case.  I can
>>> recall many networks where the DNS servers returned by the DHCP server
>>> didn't work well at all, and things got a _lot_ better when I manually
>>> configured a couple working DNS servers (e.g. the Google ones at
>>> 8.8.8.8 and 8.8.4.4).  Around here, Comcast's DNS servers are famously
>>> bad.
>
>> Then shoot the idiot running that wireless network.
>
> You're not actually allowed to do that General Dreedle...
>
>> If he's one of my juniors, tell me so I can fire him (as he's just
>> proved he can't do the job he's paid to do)
>
> And if you're at a customer or vendor site?  A friend's or relative's
> house?  Using a municiple WiFi system?  Using WiFi on an airplane,
> bus, train, whatever?
>
> Sometimes you just need to get along with people and get some work
> done.  You always can't demand that things get done your way or
> somebody's gonna get fired or taken out back and beaten...
>

Pretty much always worked for me. I'm one of the guys that sets things 
up so that guys like you have no reason to ever say "Around here, 
Comcast's DNS servers are famously bad". Replace "Comcast" with the real 
name of my real employer. If my team gets that wrong (and we never have 
thus far), millions of people immediately and at once suffer. So forgive 
me if I'm a tad touchy on the subject.

But seriously, if the dns servers provided by dhcp aren't up to snuff 
then by all means put working ones in your resolv.conf. And also help 
the owner of the network fix his config - there really is no excuse for 
setting up software to tell people to use broken or badly behaved caches.

Alan

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

[Mick]

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On Monday 11 Jul 2016 23:50:48 Alan McKinnon wrote:
> On 11/07/2016 23:03, Grant Edwards wrote:
> > On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
> >> On 11/07/2016 22:29, Grant Edwards wrote:
> >>> On 2016-07-11, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
> >>>> why don't you go with the dns server addresses supplied by each
> >>>> network's dhcp? Presumably the admin put them their because they
> >>>> work on that network.
> >>> 
> >>> One might think that, but I find it often not to be the case.  I can
> >>> recall many networks where the DNS servers returned by the DHCP server
> >>> didn't work well at all, and things got a _lot_ better when I manually
> >>> configured a couple working DNS servers (e.g. the Google ones at
> >>> 8.8.8.8 and 8.8.4.4).  Around here, Comcast's DNS servers are famously
> >>> bad.
> >> 
> >> Then shoot the idiot running that wireless network.
> > 
> > You're not actually allowed to do that General Dreedle...
> > 
> >> If he's one of my juniors, tell me so I can fire him (as he's just
> >> proved he can't do the job he's paid to do)
> > 
> > And if you're at a customer or vendor site?  A friend's or relative's
> > house?  Using a municiple WiFi system?  Using WiFi on an airplane,
> > bus, train, whatever?
> > 
> > Sometimes you just need to get along with people and get some work
> > done.  You always can't demand that things get done your way or
> > somebody's gonna get fired or taken out back and beaten...
> 
> Pretty much always worked for me. I'm one of the guys that sets things
> up so that guys like you have no reason to ever say "Around here,
> Comcast's DNS servers are famously bad". Replace "Comcast" with the real
> name of my real employer. If my team gets that wrong (and we never have
> thus far), millions of people immediately and at once suffer. So forgive
> me if I'm a tad touchy on the subject.
> 
> But seriously, if the dns servers provided by dhcp aren't up to snuff
> then by all means put working ones in your resolv.conf. And also help
> the owner of the network fix his config - there really is no excuse for
> setting up software to tell people to use broken or badly behaved caches.
> 
> Alan

All good points made here and Alan's style of leadership (...daily floggings 
will continue until morale improves) surely works in some cases.  However, in 
certain locations there are 2 or 3 open WiFi networks which I may accidentally 
associate with.  They will not let you use their network without 
registering/login in with them, using your browser.  So, when I end up 
associating with any of them, their nameservers pollute my resolv.conf and 
delays ensue every time I seek a URL.  Sometimes the WiFi network is one I 
want to associate with, but not use its relatively slower nameservers, until I 
unplug the ethernet cable and roam around the office.  There are more nuanced 
use cases (some network servers are not accessible via WiFi, but are via 
ethernet) but I don't want to complicate further the basic requirement:

It would be great if the order of nameservers entered in /etc/resolv.conf 
respected the metric of the NIC.

-- 
Regards,
Mick

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

[Emanuele Rusconi]

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On 11 July 2016 at 17:31, Alan McKinnon <alan.mckinnon@gmail.com> wrote:

> On 11/07/2016 10:32, Emanuele Rusconi wrote:
> > Wouldn't it be better to just use the same servers for both wired and
> > wireless? It's what I use and it works flawlessly.
>
> It works flawlessly *for you*, but by no means can you consider it
> correct or stable.
>
> There is no guarantee that a wired and wireless network will use the
> same dns caches.
>
> If it happens to work, great, use it. But be aware there will come a day
> when that is no longer true.


That's why I phrased my suggestion as a question. I'm honestly curious:
aren't DNS servers like Google ones (8.8.8.8 etc.) supposed to be reachable
from anywhere? If you can't reach them, isn't your connectivity inherently
broken? I'm sure I'm missing something here.

-- Emanuele Rusconi

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

[Grant Edwards]

On 2016-07-12, Emanuele Rusconi <emarsk@gmail.com> wrote:

> That's why I phrased my suggestion as a question. I'm honestly curious:
> aren't DNS servers like Google ones (8.8.8.8 etc.) supposed to be reachable
> from anywhere? If you can't reach them, isn't your connectivity inherently
> broken? I'm sure I'm missing something here.

Oh, I'm sure there's some brain-dead ISP or BofH somewhere who blocks
traffic to outside DNS servers.  Inevitably it's done in the name of
security.

Even if 8.8.8.8 is reachable, there may be internal, locally defined
hostnames that Google won't know about.

That said, after problems with various DNS servers on various
networks, I usually default to using 8.8.8.8...

-- 
Grant Edwards               grant.b.edwards        Yow! Does someone from
                                  at               PEORIA have a SHORTER
                              gmail.com            ATTENTION span than me?

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

[Marat BN]

The solution I use when dealing with the problem of network software
overwriting '/etc/resolf.conf' is to make that file immutable with
'chattr +i'.

Not quite an answer to your question on nameserver prioritization, but
could be useful to prevent your nameservers from being changed.


-- Marat



On 07/09/2016 07:53 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 line
> 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?
>