network tuning and performance troubleshooting
Bob McIsaac
bobmc at bobmc.net
Thu Jan 4 23:07:28 UTC 2007
Doug Hardie wrote:
>
> On Jan 3, 2007, at 22:57, Bob McIsaac wrote:
>
>> Problem: Browser status 'looking up address' for 10 seconds for any
>> web page clicked. Slashdot takes almost a minute to load. But FTP
>> performance is good and running a shoutcast stream is no problem.
>> Sending mail via my ISP is slow.
>>
>> Investigation: - "sysctl -a | grep net | less" shows a ton of
>> variables
>> with values assigned. Ping of nameserver assigned by dhcp takes 0.5ms.
>> Ping of freebsd.org = 90ms. Nothing obvious in loader.conf or
>> rc.conf (defaults). /var/log/messages has only startup info.
>>
>> Question: - How to solve this thorny performance problem? -Bob-
>
> You might want to run tcpdump and monitor one of those slow loads.
> Include the timestamp in the output and see what it is doing during
> that time. I would tend to suspect DNS timeouts.
>
>
tcpdump confirms there is a ten second delay as seen on the browser.
1. there are some UDP packets to/from the nameserver.
2. nothing happens for ten seconds
3. now there is a TCP connection
tcpdump: listening on vr0, link-type EN10MB (Ethernet),
17:34:07.537419 proto: UDP (17)
192.168.1.102.53032 > 192.168.1.254.domain:
45959+ A? www.google.ca. (31)
17:34:07.545218 IP proto: UDP (17)
192.168.1.254.domain > 192.168.1.102.53032:
45959 6/7/4 www.google.ca. CNAME[|domain]
17:34:07.545500 IP proto: UDP (17)
192.168.1.102.64463 > 192.168.1.254.domain:
45960+ AAAA? www.google.ca. (31)
17:34:07.868410 IP proto: UDP (17)
192.168.1.102.61375 > 192.168.1.254.domain:
48085+ PTR? 254.1.168.192.in-addr.arpa. (44)
17:34:12.545947 IP proto: UDP (17)
192.168.1.102.54649 > 192.168.1.254.domain:
45960+ AAAA? www.google.ca. (31)
17:34:12.868866 IP proto: UDP (17)
192.168.1.102.55840 > 192.168.1.254.domain:
48085+ PTR? 254.1.168.192.in-addr.arpa. (44)
<<<<<<<< nothing happens for 10 seconds?? >>>>>>>>>>>>
17:34:22.546051
(tos 0x0, ttl 64, id 226, offset 0, flags [DF],
proto: TCP (6), length: 64)
192.168.1.102.52363 > qb-in-f147.google.com.http: S,
cksum 0x3aa5 (correct),
1762925400:1762925400(0) win 65535 <mss 1460,
nop,wscale 1,
nop,nop,timestamp 1758025 0,sackOK,eol>
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