DNS expiry time in /etc/resolv.conf

Ted Lemon Ted.Lemon at nominum.com
Thu May 24 14:16:18 UTC 2012

On May 24, 2012, at 4:05 AM, Rudy Zijlstra wrote:
You canot determine that from the resolv entry points. The DNS name server can work with different expiry times even within a single domain. DHCP does not have any knowledge on this, except for dynamic DNS updates where the lease time usualy determines the DNS expiration time

There is no such thing as a "DNS expiration time" except with respect to DNSSEC key lifetimes.   DNS updates set the TTL relative to the lease time (I don't remember the exact details, and they've probably changed anyway since I wrote the code).   I presume that the OP was asking about how to expire entries from /etc/resolv.conf that have been added by the client.   The answer is that if your lease changes, /etc/resolv.conf gets updated, and I _think_ that if your lease expires, it also gets updated.   But if it doesn't get updated until a new lease is acquired, that's okay, because once your lease has expired, you're offline (unless you are running multiple interfaces, a case that is not well handled).

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