[SOLVED] DNS MX record explanation

Upendra Pratap Singh · 03-11-2015, 12:59 PM

When I write the MX record as

Code:

mydomain.com 14400 IN MX 0 mydomainname.com

What does 14400 indicate in this record?

MensaWater · 03-11-2015, 01:12 PM

It is the TTL (time to live) in seconds. 14400 seconds = 4 hours

This tells people that are checking your zone how long they can cache the record before they should recheck it.

However, just because you say 4 hours doesn't mean they will only cache it 4 hours - they can override in their DNS lookups.

A good discussion of MX records is at:
http://www.zytrax.com/books/dns/ch8/mx.html

I highly recommend that parent link as a good book for understanding DNS and for finding specific answers:
http://www.zytrax.com/books/dns/

Habitual · 03-11-2015, 01:12 PM

http://tools.ietf.org/html/rfc1035

TenTenths · 03-11-2015, 01:36 PM

Quote:

Originally Posted by MensaWater

However, just because you say 4 hours doesn't mean they will only cache it 4 hours - they can override in their DNS lookups.

From (bitter) experience some ISPs can be rather bad about respecting TTL in their cache DNS servers.

(Slightly off-topic I know, but something to be aware of)

MensaWater · 03-11-2015, 02:10 PM

Quote:

Originally Posted by TenTenths

From (bitter) experience some ISPs can be rather bad about respecting TTL in their cache DNS servers.

Yes but on the flip side this occurs because some folks do something psychotic like 30 second TTLs.

TenTenths · 03-12-2015, 03:06 AM

Quote:

Originally Posted by MensaWater

Yes but on the flip side this occurs because some folks do something psychotic like 30 second TTLs.

There are situations where it's a dictated business requirement.