[SLL] Slow DNS lookups

[Derek Simkowiak]

    Mike,
    Thanks for posting the info.  Sorry for the slow reply... I'm in the 
middle of building a new dev server...

Mike>/ followed by an AAAA record lookup on <domain-name> + ".mit.edu", 
followed by an A record lookup, which finally works. Don't know if it 
did that before or not./

    This happens because of the following line in your resolv.conf:

search mit.edu

    If you connect to a server called (e.g.) your_server.mit.edu, and 
you only want to type "your_server", then DNS will automatically figure 
out that "your_server" actually refers to the published I.P. address of 
"your_server.mit.edu". 

    But by default, the "search" option contains your local domain name, 
which is already set to "mit.edu".  So this line is redundant on your 
system (but causes no harm).

    Regarding the speed of your DNS servers, I did find them to be 
relatively slow (compared to my regular DNS servers).  But the slowness 
I am experiencing might simply be because of where I am physically 
located on the Internet; my ping time to your DNS servers is about 
102ms, and my ping time to my regular DNS servers is only 29ms.

    Given that your slowness suddenly appeared last week, I suspect that 
your DNS server administrators have made some change in the data 
center.  Perhaps they installed a new (crappy) firewall, or changed the 
routes in a way that makes it slow for you.  Or, maybe they've installed 
Battlefield 2142 on the DNS servers, thinking nobody would notice :)

    To test that the problem is with your DNS servers (and not with your 
computer), try temporarily replacing your resolv.conf with the following 
text:

domain mit.edu
search mit.edu
nameserver 208.67.222.222
nameserver 208.67.220.220

    ...and then surf the web and see if it's faster.  (Those new 
nameservers are the OpenDNS servers.)

    If it's faster, call the sysadmins at MIT and tell them to uninstall 
Battlefield off the DNS servers.

--Derek


Mike Stunes wrote:
> # Generated by net-scripts for interface br0
> domain mit.edu
> search mit.edu
> nameserver 18.70.0.160
> nameserver 18.71.0.151
> nameserver 18.72.0.3
>
>
> Derek Simkowiak wrote:
>>     Can you post your /etc/resolv.conf?
>>
>>     If they're publicly available, I'll switch to your DNS servers 
>> and see if I can reproduce the symptoms.
>>
>> --Derek
>>
>> Mike Stunes wrote:
>>> Recently I've been having an issue with name lookups, particularly 
>>> from Firefox, taking much longer than they used to. Seems like it 
>>> used to be pretty quick, and now navigating to a different site 
>>> takes several seconds, usually about four or five. (If I remember 
>>> right, this has been going on for a few days, maybe a week or so.) 
>>> Once Firefox gets past "Looking up ...", however, it's a breeze. I 
>>> can't figure out what might have changed that would cause this--I 
>>> don't remember having done any major software updates or config 
>>> changes about the time this started, and /etc/hosts and 
>>> /etc/resolv.conf look fine. Wireshark shows an interesting story-- 
>>> first, an AAAA record lookup, followed by an AAAA record lookup on 
>>> <domain-name> + ".mit.edu", followed by an A record lookup, which 
>>> finally works. Don't know if it did that before or not. Does anyone 
>>> have any idea what might be going on? Thanks in advance!
>>>
>>> Mike
>>