FYI: Mac OS X, Safari (et al), and DNS timeouts

Simon Hobson shobson0309 at
Wed Dec 22 14:10:32 UTC 2004

Just an FYI which I hope might be of help to someone else.

A couple of weeks ago I set up an internal DNS server (BIND on a 
Linux box) on my little home network, and then I started getting 
"this site could not be reached" type errors from Safari - you know, 
the ones where it almost always works second time around. After a bit 
of packet sniffing, and googling it seems that this is a known 
problem engineered into OS X by Apple !

 From observation, when I go to a website, the Mac does (up to) five 
DNS queries, at one second intervals, and with a one second timeout. 
Naturally, some resolutions can take longer than 6 seconds to 
complete and so the user gets many failures - always succeed second 
time around. Thanks a lot Apple !

I found messages on various forums about how switching to using ISPs 
nameservers cured it, and then someone pointed out that in fact the 
real reason for these 'successes' was that by listing two 
nameservers, the timeout got doubled ! Listing my own server twice in 
the DHCP config cured the problem.

I also saw comments about version Mac OS 10.3.7 including a new 
lookup tool (not just DNS) which will have some configurability.



NOTE: This is a throw-away email address which will reach me for as 
long as it stays spam-free, remove date for real address.

Simon Hobson MA MIEE, Technology Specialist
Colony Gift Corporation Limited
Lindal in Furness, Ulverston, Cumbria, LA12 0LD
Tel 01229 461100, Fax 01229 461101

Registered in England No. 1499611
Regd. Office : 100 New Bridge Street, London, EC4V 6JA.

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