Name server issue

[Speedline Z]

this has nothing to do with the hosting, but maybe someone here could provide some insight on this.

When i migrated to plesk5, i switched all of my domains over to the new IP addy on my Nameservers (xname.org and zoneedit.com) ... on one of my domains, i accidently missed updating the IP on xname, but did on zoneedit... a couple days ago i corrected this on xname.

Today my ISP now has the old IP cached for half the subdomains (including www) and the correct IP for the other half (inlcuding the domain itself)

It was to my understanding that DNS updates occurred instantly and that it takes up to 1 hour for the ISP to update its caches

so why am i still getting the old IP 2 days later

any suggestions?

[admin]

This would depend on what the default TTL is set to on the entries.  It can be one hour, or it could be days.  The "Default TTL" is set in seconds.  If it says 3600, that would be 1 hour.  This would be under your control with the DNS provider you are using.

Also, the ISP may not be honoring the TTL values (some do this to reduce traffic to their nameservers).  It could also be cached via your (or whoever's) OS resolver cache for that nameserver as well.

It could also be that one of your nameservers provided the wrong result for some reason.

The change is made instantly (of course this depends on your DNS provider), but each time you request a record (lookup), it is cached for the duration of the "Default TTL".  This would be the case if anyone that queries your ISP's nameserver requested this record.  This could also be caused by stale cache and/or modified TTL settings that override domain settings in your ISP's server.  This should not be the case, but some providers have been known to do this for their own benefit in the past.