[Dnsmasq-discuss] dnsmasq for road warriors

[sam at sltosis.org]

On Tue, Nov 13, 2012 at 09:03:03AM -0600, /dev/rob0 wrote:
> On Tue, Nov 13, 2012 at 12:13:07PM +0100, sam at sltosis.org wrote:
> > On Mon, Nov 12, 2012 at 06:11:43PM -0600, richardvoigt at gmail.com 
> > wrote:
> > > On Sun, Nov 11, 2012 at 5:05 PM, /dev/rob0 <rob0 at gmx.co.uk> 
> > > wrote:
> > > > > On 10/11/2012 15:54, /dev/rob0 wrote:
> > > > > >Seems to me that dnsmasq is a better nscd replacement,
> > > > > >and it has a place in mobile computing.
> > > > > >
> > > > > ># we use this dnsmasq as this system's own resolver
> > > > > >no-resolv
> > > >
> > > > On Sat, Nov 10, 2012 at 05:46:10PM -0600,
> > > >    richardvoigt at gmail.com wrote:
> > > > > no-resolv is doing more harm than good.
> > > > >
> > > > > dnsmasq is smart enough to ignore 127.0.0.1 in 
> > > > > /etc/resolv.conf And it will automatically pick up 
> > > > > DHCP-assigned DNS servers which written there.
> > > >
> > > > But you don't understand. The point of dnsmasq on a laptop
> > > > is to serve ONLY that machine and its local processes.
> > > > /etc/resolv.conf must contain ONLY "nameserver 127.0.0.1".
> > > > If there are other nameservers listed, the system resolver
> > > > will be contacting them; possibly getting different results,
> > > > and ... well, this discussion would not be relevant to
> > > > the dnsmasq list.
> > > >
> > > I don't know where you got this piece of misinformation.  
> > > Multiple nameserver entries in /etc/resolv.conf work fine, as 
> > > long as the localhost entry (pointing to dnsmasq) comes first.
> > 
> > It will work fine, but the system resolver might end up querying
> > an nameserver other than dnsmasq(localhost) which is exactly, if
> > I understood correctly, what /dev/rob0 wants to avoid.
> 
> Yes. And thanks to Richard for making me look in the resolv.conf(5) 
> manual. The listing order is the priority, but there's always a 
> chance that lookups could fall through from 127.0.0.1 to other 
> nameservers, and I don't want that.
> 
> > That said, dnsmasq will poll your alternate resolv.conf for change 
> > automatically, unless requested otherwise (--no-poll), so I see no 
> > need to restart it after a change.
> 
> Aha! I missed --no-poll. This looks to be pretty easy, then, using 
> --resolv-file. (And --no-resolv is moot.)
> 
> > This is actually what I was doing* on my laptop, a custom dhcp 
> > client hook will fill an alternate resolv.conf file : 
> > /etc/resolv.conf-dnsmasq (used by dnsmasq), and ensure 
> > /etc/resolv.conf only contains the localhost nameserver with 
> > optionnal supplementary parameters (search,...)
> 
> Thanks!
> 
> > This is obviously usefull for dnsmasq cache and other features (eg: 
> > server=//), but also for some services/daemons which don't poll 
> > /etc/resolv.conf for change on their own(eg: postfix)
> 
> Hehe, it seemed a bit crazy to run server software on a laptop, but 
> at least I'm not putting Postfix on there. (Yet? ;) )
> 

Well I have to admit it may sound crazy, but it is not *that* crazy if you have
a terrible connection, where a simple email can take up to a few seconds being
sent I'm using mutt and I can't do anything else during that step if using mutt
sending facilities. (now imagine a normal email with an attachment, or a
network problem and the need to try again?! no really using postfix to do part
of what it is supposed to do is a must!)


> For the archives, here's what I ended up with on the laptop:
> 
> no-dhcp-interface=lo
> listen-address=127.0.0.1
> no-resolv
> resolv-file=/var/lib/dhcpcd/resolv.conf
> user=dnsmasq
> group=dnsmasq
> server=/rob0.vpn/192.168.6.1
> server=/6.168.192.in-addr.arpa/192.168.6.1
> 
> /etc/resolv.conf contains only "nameserver 127.0.0.1". (It could just 
> as well not exist, because the default resolver behavior is to query 
> DNS from 127.0.0.1.) And dhcpcd(8) is writing domain_name_servers to 
> /var/lib/dhcpcd/resolv.conf.
> -- 
>   http://rob0.nodns4.us/ -- system administration and consulting
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> 
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