Re: peerdns reversed?

[Sean Darcy <seandarcy2 gmail com>]

On 04/23/2014 11:39 AM, Dan Williams wrote:
> On Tue, 2014-04-22 at 11:27 -0400, Sean Darcy wrote:
> > On 04/21/2014 05:28 PM, Dan Williams wrote:
> > > On Sun, 2014-04-20 at 21:15 -0400, Sean Darcy wrote:
> > > > on Fedora 20:
> > > >
> > > > cat /etc/sysconfig/network-scripts/ifcfg-external
> > > > # Please read /usr/share/doc/initscripts-*/sysconfig.txt
> > > > # for the documentation of these parameters.
> > > > TYPE=Ethernet
> > > > BOOTPROTO=dhcp
> > > > DEVICE=external
> > > > DEFROUTE=yes
> > > > IPV4_FAILURE_FATAL=no
> > > > IPV6INIT=no
> > > > PEERDNS=no
> > > > DNS1=127.0.0.1
> > > > DNS2=8.8.8.8
> > > > ## PEERROUTES=yes
> > > > USERCTL=no
> > > >
> > > > cat /etc/resolv.conf
> > > > # Generated by NetworkManager
> > > > nameserver 127.0.0.1
> > > > nameserver 8.8.8.8
> > > >
> > > > but if I set PEERDNS=yes:
> > > >
> > > > cat /etc/resolv.conf
> > > > # Generated by NetworkManager
> > > > nameserver 167.206.251.130
> > > > nameserver 167.206.251.129
> > > > nameserver 127.0.0.1
> > > > # NOTE: the libc resolver may not support more than 3 nameservers.
> > > > # The nameservers listed below may not be recognized.
> > > > nameserver 8.8.8.8
> > > >
> > > > Isn't this the wrong way around?
> > >
> > > Currently any additional static DHCP servers are appended to those
> > > detected from DHCP.  So I think this is the intended functionality.  I'm
> > > assuming you'd rather have them prepended instead?
> > >
> > > But since you're using 127.0.0.1, it seems unlikely that you want any
> > > nameservers at all, but you'll want to use a local caching nameserver?
> > > NM has some built-in functionality for that already using dnsmasq, see
> > > 'man NetworkManager.conf' in the section about DNS.
> > >
> > > Dan
> >
> > Thanks for the reply. I'll look at dnsmasq. Thanks for the lead.
> >
> > But really I'm just trying to overide the isp's dns servers. I've looked
> > up PEERDNS in sysconfig.txt, from Fedora's initscripts-9.51-2.fc20.
> >
> > PEERDNS=yes|no
> >         modify /etc/resolv.conf if peer uses msdns extension (PPP only) or
> >         DNS{1,2} are set, or if using dhclient. default to "yes".
> > DNS{1,2}=<ip address>
> >         provide DNS addresses that are dropped into the resolv.conf
> >         file if PEERDNS is not set to "no".
>
> > As I read this, if PEERDNS is set to "no" the DNS addresses not dropped
> > into resolv.conf. If "yes", they are, but no mention of pre- or ap- pend.
>
> Your reading appears to match the code in ifup-post.
>
> > Now if you set PEERDNS to "no" NM puts only the connection DNS addresses
> > in resolv.conf. If "yes" NM appends them to the dhcp adresses.
>
> Correct, NM's interpretation does appear to be different.
>
> > I prefer the wholesale replacement, since I don't want to use the isp's
> > servers, so I probably shouldn't complain about the inconsistency. Is
> > the way NM handles the entries in the ifcfg- scripts described anywhere?
> > Perhaps I should not have been looking at sysconfig.txt?
>
> For the ifcfg file format, the goal is to keep NetworkManager's
> interpretation as close to the old initscripts as possible.  So in the
> vast majority of cases, there should be no difference between
> sysconfig.txt and NetworkManager.
>
> However, there are some areas where differences occur, and it looks like
> you've found one.  Our documentation needs to be better, and I've filed:
>
> https://bugzilla.gnome.org/show_bug.cgi?id=728802
>
> to track the issue.  Thanks for the report!
>
> Dan

Thanks.

FWIW, I prefer the way NM handles PEERDNS now, rather than the 
description in initscripts. Of course, I don't know whether the network 
stack prepends or appends the DNS addresses from the scripts when 
PEERDNS is set yes.

sean