network tuning and performance troubleshooting

[Bob McIsaac]

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>