SOA "minimum" vs "negative ttl"

Jack Tavares j.tavares at
Thu Jan 24 01:05:33 UTC 2013

I believe that RFC 2308 redefines the SOA "minimum" field to be
"negative ttl"

If I create a dynamically updated zone file that looks like so:

$TTL 500 IN SOA 2013012301 10800 3600  604800 86400 IN NS

When a DNS update comes into to add or modify a record and bind eventually re-writes
the master file it will rearrange the SOA and add comments (which is fine) but it labels
the last field as "minimum"

$TTL 500	; 8 minutes 20 seconds			IN SOA (
				2013012302 ; serial
				10800           ; refresh (3 hours)
				3600             ; retry (1 hour)
				604800         ; expire (1 week)
				86400           ; minimum (1 day)
a			A

Is there a reason for this or is it just a hold over?
It is perpetrating a misconception that this is the minimum TTL.


Jack Tavares

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