DNS Issues [Was: [gentoo-user] Re: Slow Login, Sudo, etc.]

[daid kahl]

On 13 October 2010 22:38, daid kahl <daidxor@×××××.com> wrote:
>> On 10/11/2010 11:38 PM, daid kahl wrote:
>>
>>> However, I noticed that logins, su, and sudo are all responding
>>> slowly.  This was all fixed and fine once I updated my configuration
>>> files, but this week it's acting up again.  Before it was just su and
>>> sudo that I noticed as slow (authentication takes around 20 seconds).
>>> But now even logins are delayed (xdm or command line).
>
> On 13 October 2010 07:12, walt <w41ter@×××××.com> wrote:
>>
>> Whenever I see something that eventually works, but only after a long
>> delay, I think of DNS problems.
>>
>> Who might be doing a nonsensical DNS lookup, I have no idea.  But you
>> might consider running a packet sniffer (wireshark, etc) while logging
>> in or doing an su.  Are you running your own local name server?
>
> Very very intersting!!
>
> The main correlation I've seen so far is with dhcpcd.  Sometimes at my
> work I get a 192. IP (which doesn't work), and other times I get a
> 133. IP (which is correct).  In fact, sometimes dhcp is giving me an
> IP address and resolv.conf related to a university I was visiting like
> a month ago.
>
> In other words, I know I have some networking problems, but I was
> reluctant to imagine it was at all related to this login problem, even
> though I had some basic empirical data on it.
>
> Anyway, it happened again tonight, and it was resolved after I did
> some of the same emerges as before, but I think that might be just
> chance.
>
> I look into the DNS stuff.  Thanks for the sanity check!
>
> ~daid
>
> PS: Sorry for the initial top posting on myself...
>

I've been having some networking problems lately, and apparently it's
mucking up my logins and things like sudo sometimes as well.  Thanks
to Walt for telling me these two problems might be related.

I'm on a MacBook, and I wouldn't say this is the first time I've had
networking issues, but the hardware may not be at all the problem.

At home I use wireless and NetworkManager for that.  This is because
I've never managed to get wicd working correctly for my wireless.
Just tonight I had to stop dhcpcd for NM to actually connect.  Maybe
this is normal, I kind of forget how I hack things sometimes, though.

At work I'm using DHCP, and the nameserver is controlled by the
network.  In that case, if I reboot, I (sometimes) get a correct IP.
Normally I'm on top of what's controlling what, but I'm more confused
these days.  I can't tell if it's done by net, or dhcpd or what, since
restarting them doesn't usually reboot net.eth0.  Sometimes I get wicd
working on it.  It's kind of a mess!

Very curiously, as in my previous post I mentioned, sometimes I'm
getting resolv.conf for a university I visited like last month.  Why
or how that would happen I don't know.  It's some config problem?  I
need to dig through everything, since sometimes at the university I
statically connect, but I'm pretty sure all those are commented out.
Why it will assign me up to three different nameservers, seemingly
randomly, for ethernet, I can't understand.

So, firstly I'll need some troubleshooting.  I already have wireshark
installed, so that could be helpful.

I guess what might be helpful right now is how to purge my networking
stuff and just start it all from scratch.  There is so much garbage
installed right now so I can hack it together that it's just a mess
(this happened because I can get it to function eventually, yuck).

Cheers,
daid