DNS 'A" record format question

[Sean OB_1]

Does anyone know if this is a valid entry?

machinename 0 IN A nnn.nnn.nnn.nnn

I have 3 entries in one zone that have a "0" after the machine name.

I've never seen that format before, should I remove the "0" or is it used for something?

TIA,

Sean

[Jeff Schussele]

Hi Sean,

I've never seen that.
Does it resolve properly now?

Test it w/o the 0 - does it resolve properly then?
If not, just put it back.

Rgds,
Jeff

[Sean OB_1]

Sorry I should have mentioned that it is resolving correctly with the "0" in the entry.

[Jordan Bean · Accepted solution]

That zero is the optional TTL for the record and dictates for how long a client will keep the record in cache. A value of zero means never cache it and does not work with some older BIND versions. If absent, it defaults to the TTL of the zone (defined in the SOA or with $TTL at the top of the zone file).

[U.SivaKumar_2]

Hi,

I am using the syntax with zero TTL like this
for DNS failover (Round-robin) .

www 0 IN A 201.1.1.1
www 0 IN A 201.0.2.1
www 0 IN A 203.0.0.0

The zero TTL here prevents the nameserver's caching the above Address records so that the failover will be fast.

regards,
U.SivaKumar

[Jeff Schussele]

Well now I've learned something & I can go home now.

Wait I'm home already.......

Thanks Jordan...that's why I hang out here. You'll always learn something!

Sean..that's a tenner!

Jeff