Re: [courier-users] MX randomizing: trying to understand the

Sam Varshavchik wrote:

> Rodrigo Severo writes:
>
>> Sam Varshavchik wrote:
>>
>>> The DNS server already returns DNS records in random order.
>>
>>
>> I believe that by "random order" you mean a different random order
>> for each query. If this is the case I would like to ask to which DNS
>> servers do you refer specifically?
>
>
> Anyone heard of "bind"?

Yeah. Sure...

>> Could you please advise on how can I get a more random MX choosing by
>> Courier?
>
>
> Stop using broken DNS caches.

That's not exactly what I wanted to hear but I can live with it.

> By definition, the only function of a cache is to speed up lookups.
> An application that uses a cache, be it a DNS cache, a web cache, or
> any other kind of cache whatsoever, should NOT be aware that it's
> using a cache, and not the real thing. It should get the same reply
> that it would get from the real thing. Except that it would get the
> reply faster.
>
> Therefore, it is the caching software's complete and full
> responsibility to behave and act in every way like the real thing,
> except that it's faster.

Does anybody knows of any suitable solution for this issue besides bind?
I want by all means not to go back using bind if at all possible.

> Real DNS servers return record in random order. Therefore, a properly
> implemented cache will also return records in random order. If it
> doesn't, it's broken and it needs to be fixed.

Let me suggest that this issue get some explicit treatment in Courier's
documentation. Something like the following observation:

------------------------------------------------------------------------------------------------------------------------------
Courier relies in the randomness of the internal order of the DNS
replies it gets for better load balancing and reliability during message
delivery.

Known non-random (not siutable) DNS caches:
DJB's dnscache;
glibc's nscd.

Known random (suitable) DNS caches:
bind.
------------------------------------------------------------------------------------------------------------------------------


Thanks again for your clarifications,

Rodrigo Severo



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