Slow connection/dns lookup with some command line applications

felace · 2011-03-27 11:09:11

Hi.

There are similar topics on slow dns lookup problems, but I have yet to find a solution after three months of research. Shortly put, programs such as wget and pacman work really slow, requiring a significant amount of time to establish a connection to the destination. For instance, whenever I try to upgrade some packages or get package lists using pacman, each of them takes about 5-10 seconds before being downloaded.

time pacman -Sy
:: Synchronizing package databases...
core is up to date
extra is up to date
community 431.7K 492.6K/s 00:00:01 [######################] 100%
archlinuxfr is up to date
real 0m22.604s
user 0m0.010s
sys 0m0.013s

time wget www.python.org
--2011-03-27 14:24:46-- http://www.python.org/
Resolving www.python.org... 82.94.164.162, 2001:888:2000:d::a2
Connecting to www.python.org|82.94.164.162|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 19174 (19K) [text/html]
Saving to: “index.html.12”
100%[======================================>] 19,174 104K/s in 0.2s
2011-03-27 14:24:52 (104 KB/s) - “index.html.12” saved [19174/19174]

real 0m5.511s
user 0m0.003s
sys 0m0.003s

Strangely though, ping and dig work without any slowdown :

ping -c 4 www.facebook.com
...
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 155.083/155.515/156.326/0.679 ms

dig google.com a
; <<>> DiG 9.8.0 <<>> google.com a
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45663
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 167 IN A 74.125.87.104
google.com. 167 IN A 74.125.87.99
;; Query time: 75 msec
;; SERVER: 192.168.2.1#53(192.168.2.1)
;; WHEN: Sun Mar 27 14:31:31 2011
;; MSG SIZE rcvd: 60

Packets observed while using pacman (similar results with wget ; it re-queries after ~5 seconds) :

No. Time Source Destination Protocol Info
1 0.000000000 192.168.2.3 208.67.222.222 DNS Standard query A mir.archlinux.fr
2 0.000030000 192.168.2.3 208.67.222.222 DNS Standard query AAAA mir.archlinux.fr
3 0.079779000 208.67.222.222 192.168.2.3 DNS Standard query response A 213.186.62.207
...(some other wireless network traffic)
6 5.004815000 192.168.2.3 208.67.222.222 DNS Standard query A mir.archlinux.fr
7 5.077155000 208.67.222.222 192.168.2.3 DNS Standard query response A 213.186.62.207
8 5.077210000 192.168.2.3 208.67.222.222 DNS Standard query AAAA mir.archlinux.fr
9 5.159977000 208.67.222.222 192.168.2.3 DNS Standard query response
10 5.160091000 192.168.2.3 213.186.62.207 TCP 49408 > http [SYN] Seq=0 Win=5840 Len=0 MSS=1460 SACK_PERM=1 WS=7
11 5.250785000 213.186.62.207 192.168.2.3 TCP http > 49408 [SYN, ACK] Seq=0 Ack=1 Win=5840 Len=0 MSS=1460 SACK_PERM=1 WS=4
...

But dig doesn't indicate such a problem :

No. Time Source Destination Protocol Info
1 0.000000 192.168.2.3 208.67.222.222 DNS Standard query A mir.archlinux.fr
2 0.072413 208.67.222.222 192.168.2.3 DNS Standard query response A 213.186.62.207

I thought of using another router since the problem arose upon changing it, however :

Web browsers work fine : Chromium has no problem, Firefox "fixed" upon disabling its ipv6 option.
Windows and OSX which we have installed on other computers all work fine. I have just tried an Ubuntu live disk on this computer and it worked normally as well. Tested with different dns servers (opendns,google dns,etc) but observed no difference.

Here's what I've done so far :

Disabled ipv6 module for sure. I don't understand why there are AAAA requests, though.

host -6 www.google.com
host: can't find IPv6 networking
ip a | grep inet6
-nothing-

Used options rotate and options single-request in /etc/resolv.conf. The file is immutable, I'm sure they don't get deleted.
Used sysctl -w net.ipv4.tcp_timestamps=0
/etc/nsswitch.conf has hosts: files dns

Any suggestions ?

theringmaster · 2011-03-30 04:28:05

I have wiped my machine and I am now reinstalling arch on it. I too experience this massive slow down with pacman and wget. I couldn't tell at first wither not not that it was the entire system or isolated to net applications.

twarkie · 2011-04-16 20:14:25

I have the exact same problem with my HTPC, which results in really slow pacman updates and xbmc scraping. Seems like a waste of time to reinstall the entire machine so it would be nice to get some help with this. From what I can tell the setup is almost identical to my workstation which works fine.

akawaka · 2011-06-12 15:40:19

Could you post the output of

tcpdump -n port 53

while running wget or some other application that has slow DNS queries?

Arch Linux

#1 2011-03-27 11:09:11

Slow connection/dns lookup with some command line applications

#2 2011-03-30 04:28:05

Re: Slow connection/dns lookup with some command line applications

#3 2011-04-16 20:14:25

Re: Slow connection/dns lookup with some command line applications

#4 2011-06-12 15:40:19

Re: Slow connection/dns lookup with some command line applications

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