RBL cache {Scanned by HJMS}

[Antony Stone]

On Saturday 13 September 2003 2:40 pm, Ugo Bellavance wrote:

> I don't want to make a caching DNS. I know how to do that already.  What I
> mean is, for example:

A slight change in terminology might help you understand that what you ask is 
what happens already:

> 1-You get a message from domain.example.com.  Mailscanner checks with the
> RBL.  The RBL finds it is on a spamlist.  Mailscanner identifies the
> message as spam, puts the domain at example.com in a local cache, sets a ttl
> of, say, 4 hours.

MailScanner checks with the RBL.   This is a DNS lookup (that's all RBL 
checks are), so MailScanner is asking your local DNS, which asks the remote 
RBL DNS server.   When the response comes back, your local DNS caches it 
(because that's what DNS servers do), and tells MailScanner the result.   No 
need for MailScanner to do anything else with domain at example.com - it's 
already identified as a spam source.

> 2-Five minutes later, you get another message from domain at example.com.  In
> the current setup, to my knoledge, the RBL must be contacted again.

Well, MailScanner does another RBL check, yes, however just as last time, 
this is just a lookup to your local DNS server, which this time sees that it 
already has the answer, so it doesn't need to contact the remote RBL; it just 
tells MailScanner the same response as last time from its local cache 
(because this is precisely what DNS servers do).

> In my
> suggestion, MailScanner looks in its local cache to see if
> domain.example.com is on the spam list.  It is on the spam list, so it
> won't have to contact the RBL again for this address.

MailScanner doesn't have such a "local cache, but your local DNS server does, 
so either way there's no need for the remote network lookup.

> I think this suggestion would decrease the load on the RBL servers and on
> the network, and it would allow faster processing, since it is faster to do
> a local query than a network query.

The only thing you can't do which you had in your suggestion above was to 
specify the TTL yourself, however (as has already been pointed out here 
recently), the maintainer of the RBL is probably in a better position to 
decide this than you are, so leave it as it is when it hits your local DNS 
server.

Regards,

Antony.

-- 

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Atheists believe there is no God.

Does that make me an agnostic atheist if I do not believe there is no God?