DNS CACHING

[Simon P White]

I'm not an expert on DNS but have been asked to find out if DNS caching has an automatic timed invalidation? If so is this value configurable?

[Steven E. Protter]

Shalom Simon,

DNS caching is usually determined by the dns records for the domain. If the "release date" as I call it is updated, that usually tells ISP's to get another copy of what they cached.

The timeouts are in the dns record in /var/named by domain.

There is something similar in Windows DNS servers.

SEP

[Sivakumar TS]

Every DNS server has one /etc/named.data/db.domain file for each
domain for which it is authoritative.

This file must contain an A (address) record for every host in the zone.

I have attached the sample ds.domain file for you reference, in which the expiriration if the records can be configured ( in seconds)

604800 ; Expires after a week

[rick jones]

Indeed, the DNS specs include a TTL for resource records - intended to tell caches and the like how long to hold-onto a given resource record.

It is possible I suspect that a specific DNS caching solution could have an additional mechanism that configured it to discard the cached entries in a time less than the TTL in the DNS replies. That would be in the documentation for the specific caching solution.

Heck, I suppose it could offer an option to keep the entry for longer than the TTL, but that would be at best anti-social :)