srv lookup in record

Grant Taylor gtaylor at
Tue Aug 25 23:48:09 UTC 2020

On 8/21/20 4:26 PM, Marc Roos wrote:
> Is it possible to use srv lookups, like eg cname. I do not want to 
> create SRV record, I just want to 'get' the ip addresses, that I 
> would get vai srv lookup.

I don't know of any over the counter - if you will - way to do what - I 
think - you want to do.

> Say I have this task
> [@temp3]$ dig +short server.test.marathon.mesos

Are these the IP addresses that the names in the following SRV records 
resolve to?

> [@temp3]$ dig +short srv _http-apps._server.test._tcp.marathon.mesos
> 0 1 31024 server.test-usbzr-s3.marathon.mesos.
> 0 1 31852 server.test-z9x84-s3.marathon.mesos.
> 0 1 31790 server.test-k7g8r-s4.marathon.mesos.
> [marc at os0 temp3]$ dig +short srv 
> _http-demo._server.test._tcp.marathon.mesos
> 0 1 31791 server.test-c8g8b-s4.marathon.mesos.
> 0 1 31025 server.test-wtbza-s3.marathon.mesos.
> 0 1 31853 server.test-d0x87-s3.marathon.mesos.
> I would like to only make available the ip addresses that are in the 
> same range. If I would use a cname like this:

What does "same range" mean in this context?

Is it the client's IP range?  Or is it the server's IP range?  Or some 
reference to _http-apps vs _http-demo?

To me, the following three owner names are completely independent of 
each other.

  - server.test.marathon.mesos
  - _http-apps._server.test._tcp.marathon.mesos
  - _http-demo._server.test._tcp.marathon.mesos

I see how we as humans can probably correlate the three.  But I don't 
see how BIND will do it.

> server.local.	CNAME	 server.test.marathon.mesos.

That seems like a simple enough alias.  Simple enough that I think that 
it's existence can largely be ignored and focus on the IP extraction 
from SRV record(s) that I think you're asking about.

> I would get 6 of which 3 ip addresses are not in the same range. So I
> need to have something like
> server.local.	???	 _http-apps._server.test._tcp.marathon.mesos.

How are you going to convey the "???" portion in the owner name of the 
DNS query?

> Is this possible in bind-9.8.2-0.68.rc1.el6_10.3.x86_64?

I don't think what - I'm speculating - you want is possible as is with 
stock BIND.

I do wonder if you might be able to write a custom Dynamic Loadable Zone 
database (?) driver that might be able to do what you want.

Specifically, if you could create a DLZ driver that could take the query 
name, apply some logic to it (to determine the "???" above), perform the 
proper resolution of the SRV record(s), post process, and return the 
desired result to the original DNS query.

$Marc's_Request   IN   CNAME

Link - BIND DLZ Home

Aside:  I think this is atypical of BIND.  But I also think that it 
/may/ be in BIND's wheel house to ... hack a possible solution to.

Further aside:  I have wondered about a custom DLZ that would return the 
client's IP address (as seen by the server).  I'd like to roll my own 
"what's my IP" type service.  }:-)

Grant. . . .
unix || die

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