Re: Slow connections - DNS problems?
On Wed, 24 Mar 2021 17:13:20 -0400
Cmdte Alpha Tigre Z <santiagopinth@gmail.com> wrote:
> El mié, 24 mar 2021 a las 10:45, Andrei POPESCU
> (<andreimpopescu@gmail.com>) escribió:
> >
> > On Mi, 24 mar 21, 10:34:54, tomas@tuxteam.de wrote:
> > > On Wed, Mar 24, 2021 at 09:24:28AM +0000, Darac Marjal wrote:
> > > >
> > > > On 24/03/2021 05:32, Charlie Gibbs wrote:
> > >
> > > [...]
> > >
> > > > > # Generated by NetworkManager
> > > > > search telus
> > > > > nameserver 192.168.0.1
> > > > > nameserver 75.153.171.122
> > > > > nameserver 2001:568:ff09:10a::56
> > > > > # NOTE: the libc resolver may not support more than 3
> > > > > nameservers. # The nameservers listed below may not be
> > > > > recognized. nameserver 2001:568:ff09:10b::122
> > > > >
> > > > > My home router (supplied by Telus, notice the "search" line)
> > > >
> > > > Just another point to add to what other people are saying. This
> > > > line looks a bit suspicious to me. The "search" line is
> > > > _supposed_ to be a list of domains which your computer is part
> > > > of. It's implemented such that, when the resolver is asked to
> > > > look up a short name (e.g. "printer" or "my-laptop" etc), then
> > > > each item in the search list will be appended in turn and a
> > > > lookup made. So, for example you could have "search example.com
> > > > example.net" and a lookup for "gateway" would try
> > > > "gateway.example.com" then "gateway.example.net" in turn.
> > >
> > > [...]
> > >
> > > Well spotted. The "search telus" looks completely bogus, too.
> > > Unless you'have set up a local DNS with the "fake" TLD telus, but
> > > then, you'd probably know ;-)
> >
> > This was likely set up by the Telus home router and provided via
> > DHCP to all local systems.
>
> Well, I'm not pretty sure about this subject but... When I was
> setting up an OpenWRT router I saw there was a thing called "local
> domain", it looks like the router had a DNS that answered queries for
> that local top level domain, which had the hostnames of the devices
> connected to the router as subdomains. So, for example, if you had a
> device called "my-pc" and your local TLD was "telus",
> the writing "my-pc.telus" would send a DNS query to the router and
> it will answer with the IP address of that device.
> The router indeed used the DHCP to broadcast that local domain.
>
> In order for that local domain to work, the router needed to have a
> DNS server running and configured to answer such queries, the DHCP
> server had to pass the device's hostnames to the DNS someway, and the
> router had to be announced as a DNS server to the devices connected
> on LAN by DHCP. If you override the router DNS, the local domain
> will not work.
>
> Perhaps the router's DNS server redirects non-local queries to
> upstream servers and maybe those DNS servers broadcasted by the DHCP
> are a little slow; together, that could introduce a little delay for
> DNS responses. If you can, you could try to make the router send a
> known fast DNS server as the first DNS and then itself as the second
> DNS (if you want to keep the local domain).
>
> As I said, I don't know too much about this, so please correct me if
> I'm wrong.
>
A little. Even using root hints as a DNS server source should not
introduce a noticeable delay, whereas a client trying its number one DNS
server and getting no reply will cause a delay of 5-30 seconds. Once
the client has given up and found a working DNS server, it will normally
stick with that one for a while, maybe half an hour, before retrying
the first. Also, repeated calls to the same URL will normally get their
IP address information from the client's cache, further confusing
attempts at troubleshooting.
It is usually possible to override a poor choice coming from a DHCP
server, client computers have a DHCP client which can be configured to
either accept or refuse the values provided by the server. I'm not sure
how Network Manager deals with this, as I only use it on my mobile
computers, and not on my main network machines. Besides, I control the
DNS and DHCP servers in my network, and they do as they are told,
something that an ISP-supplied router usually doesn't. To be fair, the
ISP is only trying to cut down on finger-trouble service calls.
--
Joe
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