Host Records Priority -- Bind 9.2.4

[Chris Buxton]

On Oct 3, 2008, at 1:06 AM, Stephane Bortzmeyer wrote:
> On Mon, Sep 29, 2008 at 11:26:25AM +0530,
> Saju C <csajukuttan at hotmail.com> wrote
> a message of 10 lines which said:
>
>> Please confirm whether we can create A Record PRIORITY using the
>> current bind version or not.
>
> [A records? People still use them? Not everyone is running IPv6?]
>
> The only solution is probably the SRV record, which allows to define
> priorities.
>
> http://en.wikipedia.org/wiki/SRV_record

The SRV record requires that (a) there is a standard definition of how  
SRV is applied to the protocol in question, and (b) the client look  
for SRV records. Most protocols don't have the necessary standard  
definition of how they work with SRV records.

>> If not possible in which version it is available and how?
>
> It is a DNS issue. The DNS protocol does not have provisions for this
> sort of things. No implementation can do it.

That's not strictly true. Look at lbnamed, or the load balancing and  
fault tolerance routine of the old QuickDNS Server for classic Mac OS  
(not Mac OS X). Records are not simply returned in a particular order;  
instead, just one record of the set is returned to any given request,  
based on the state of each server (up, down, loaded, unloaded) and  
possibly on configured traffic ratios.

The mechanism is problematic, but these two examples do show that any  
given implementation can do many things above and beyond the details  
of the DNS protocol.

Chris Buxton
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