NS records with different TTL

[Gaurav Pathak]

Hi,

I have a question regarding TTL and NS records. I conducted following
tests on my dns server and found the following.

When you specify 2 NS records as different TTL as below:

xyz.com.        1D      IN      NS      ns1.xyz.com.
xyz.com.        2D      IN      NS      ns.xyz.com.

The dig response is as follows:

xyz.com.                86400   IN      NS      ns1.xyz.com.
xyz.com.                86400   IN      NS      ns.xyz.com.

When the NS records entered as below:

xyz.com.        2D      IN      NS      ns1.xyz.com.
xyz.com.        1D      IN      NS      ns.xyz.com.

The dig response is as follows:

xyz.com.                172800  IN      NS      ns.xyz.com.
xyz.com.                172800  IN      NS      ns1.xyz.com.

Note the TTL value in response, it's the TTL of the first NS record. So
what bind is doing here is parsing the TTL of first NS record and taking
the same value as the TTL value for all the NS records. My question is:

1) Why does bind behave in such fashion?
2) Is it possible to have 2 or more NS records for a zone with different
TTL values?
3) Is this a thumbrule that 2 or more NS records MUST have the same TTL.
If not then how can I make my bind understand different TTLs for NS
records?


Thanks in advance,
Gaurav