> On Mon, Sep 01, 2003 at 01:49:12PM +0000, Shane Hollis wrote: > > sigh ... i didn't explain myself fully enough ... my concern is not with > > lookups but with changes in caches. I have had a number of situations > > where caching has resulted in DNS changes being a pain in the neck and > > not propogating correctly. This is especially true when working with > > overseas clients. > > > > To sit on the backbone in the USA gives me a quicker dissemination of > > changes to DNS entries. The lookups are heirarchical .. this I know, as > > you have mentioned you look up the closes and work outwards until you > > find it but caching sometimes mucks this up and so to make changes it is > > easier to start with the main servers and work down to the smaller > > servers, not the other way around. >....> > I'm afraid I'm with both Nick and David again... > > I think you've got yourself all confused, since location has no bearing > whatsoever on how fast or slow DNS changes take effect... Yes it does ... the more 'authorative' a dns server the more 'non-authorative' DNs servers it affects. I explain it more fully in another email.
At the risk of repeating myself. .... If I change a DNS entry on a server in my bedroom that affects my domain then the change has to go to another dNS upstream of me ( maybe my ISP ) then that pushes changes upstream ... until eventually it hits someone upstream of your ISP (maybe Waikato) who then tells your isp who then tells you. If I had told the DNS at Waikato then you would have known faster than me teling my server, or isp or their isp. Here is a table of two changes possibilities. I will assume a change time of 1 hour for refreshing cahes on all machines. I will also asume a worst case senario where every downstram server queries an upstream server one minute before the upstream server refreshs its cache. Change time is 00:00 hours. There are five servers involved: My server at home(Me1) My ISP (Me2) Waikato (W) Your ISP (You2) Your server (You1) For me to refresh Me1 and to get changes to you would look like this....no changes pushed, relies on boradcast requests for changes Time Server Time_change_Registers 00:00 Me1 00:00 01:00 Me2 Told by Me1 when asked for changes and queried my DNS 02:00 Waikato Changes as asked me2 or me1 02:59 you2 Told by waikato when asking for changes 03:58 You1 Told when asking you2 Total time for You1 to change is 3:58:00 For me to refresh Me1 and to get changes to you would look like this....with changes pushed to other servers Time Server Time_change_Registers 00:00 Me1 00:00 00:00 you2 No change as asked waikato and waikato didn't know 00:01 Me2 00:01 Told by Me1 - I am being generous and pushing the change 00:02 W 00:02 Told By Me2 - Waikato is being generous and pushing a change 00:59 you1 No change as you have queried You2 01:00 you2 Changes as asked Waikato 01:59 you1 Changes to DNS as you1 asked You2 which is now changed Total time for you1 was 1:59:00 Total time for me1 was 00:00 For me to refresh waikato the change looks like: Time Server Time_change_Registers 00:00 W Changed at 00:00 00:00 you2 Knows as asked Waikato 00:59 you1 Knows as asked you2 Total time for you2 to change is 00:59 Half the time in a short chain of change with no pushes of the changes. In routing terms you normally push a change to the most authorative server first and let it filter down from there. If I want to start a rumour I don't tell Mary Hide at home, I tell Paul I'll broadcast this crud to everyone Holmes. Same way, if I want to make routing changes or major, world wide effective DNS changes start in the most authorative place I can ... for me this would possibly be Pacfic ARIN type server or the US depending on what it caches and how quickly I want changes to replicate. I have changed my domain in the US and been up and running with other clients receiving changes in less than 15 minutes. It wouldn't happen if I only changed things at paradise or at home. It all dpepnds on how authorative the server you are asking and how much you trust their cache.... The other factor in all this is the stability and up time of the network ... the backbone in the US is always up (comparitively), collects more traffic and is faster. There are more users in the US and more important servers there. Same thing as spreading the plague. Better off to do it in a crowded mall in a large density population of a huge city with excellent communting and many connections than in the corner dairy on Goslow Street, Brunner. My numbers above are probably out, I have the headache from hell but they get the point across. Hope this clarifies things... -- Shane Hollis Notes Unlimited New Zealand Ph: 021 465 547 Email: [EMAIL PROTECTED]
