Re: SMTP servers behind firewall....

From: Don Kelloway (dkelloway_at_commodon.com)
Date: 05/28/03 

Date: Wed, 28 May 2003 05:08:10 GMT

"Lars M. Hansen" <badnews@hansenonline.net> wrote in message
news:05p7dvcgm5c2akarf4mj5vskamlsitavgd@4ax.com...
> On Tue, 27 May 2003 21:20:05 GMT, Don Kelloway spoketh
>
> >"Winter" <Respond@InThis.Group> wrote in message
> >news:QZKAa.114$vi4.16924@news0.telusplanet.net...
> >> Would this eliminate problems with the MX records as well?
> >>
> >
> >If the A record that the MX record is specifying is entered into the
> >hosts file, it should alleviate the need to query DNS. This is
because
> >the hosts file is loaded into memory/cache when the system is
restarted.
>
> No, it isn't. If that was true, then changes to the hosts file would
not
> be immediate, but require a reboot. When a request for a lookup is
done,
> normally, the content of the hosts file is scanned, then if it's not
> found there, it'll make the request to the DNS server(s).
>
> With OS's like W2K and XP, there's a local DNS caching service, which
> will cache DNS entries until it's expiration time (or next reboot,
> whichever comes first). It is possible (I've never tested it) that the
> DNS caching service on W2K and XP will read and cache the content of
the
> hosts file on startup, but the file is still checked with every
lookup.
> The order of lookup on these systems are: local cache, hosts, DNS
> server.
>
> Un*x based systems works a little different, as you can specify the
> order of lookup (default is hosts, bind)
>
>
> Lars M. Hansen
> http://www.hansenonline.net
> (replace 'badnews' with 'news' in e-mail address)

As I said. It's been awhile since I have had to play around with
populating hosts files. <grin> When I was playing around. It was with
NT4 and I do remember having to reboot the system in order for it to
incorporate the entries I added or modified. But if you're right about
the process not requiring a reboot. Then I say this is excellent news
as there's one less step involved. 

-- 
Best regards,
Don Kelloway
Commodon Communications
Visit http://www.commodon.com to learn about the "Threats to Your
Security on the Internet".

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