[Sysadmins] DNS....

Alan Doherty alan at alandoherty.net
Wed Jan 6 14:23:11 GMT 2010

>Date: Wed, 6 Jan 2010 11:36:50 +0000
>From: Harry Duncan <usr.src.linux at gmail.com>
>Subject: [Sysadmins] DNS....
>To: Irish System Adminstrators discussion <sysadmins at lists.stdlib.net>
>        <49c76a811001060336y7539e08dybb01a815f5f175 at mail.gmail.com>
>Content-Type: text/plain; charset=ISO-8859-1
>Hi Guys,
>I have a customer who want to run their web/email/dns all on site
>behind a DSL line. I think its an incredibly dumb thing to do given
>the qos on the lines, but how or never, its what they want and thats
>What I am wondering is, if I add say a third DNS server to their
>domain record, one which is not "on site" behind their ADSL modem,
>which has very short TTL's and have it point the www record to a
>different webserver which would host a friendly customised error page
>saying we're experiencing difficulties at the moment, here are our
>contact numbers and we hope to be back soon ...... what is the
>likelyhood of that being accessed when the main site is available or
>do different systems randomly query DNS servers and not necessarily in
>the order they are listed?
>Are there any other safer schemes that people have used to achieve the same end?

yes it is an incredibly dumb move 
{for DNS} 

as downtime* on their DSL would effectively mean emails sent before the downtime
would likely be rejected by receivers due to their domain being non-existent

email hosting on dsl is a non-issue as senders will re-try {usually for 6 days}
and webservers on dsl {although not so common} are fine too as people expect downtime occasionally

if the customer where mine I would
A host dns externally {authoritive DNS} it costs nothing, their are many reliable high-uptime servers willing to provide DNS secondaries for free {they are free just to dissuade this sort of internet breaking idiocy}
and they can happily host the {hidden} primary internally and thus have changes made/live as fast as their own ttl allows

for additional merit badge

B host their main webserver externally www.example.com

C whatever app/archive/data they were considering important enough to necessitate local hosting {or to expensive to externally host} could be accessible and linked on http://appname.example.com and if they really wanted it to be indistinguishable from their main site they could wrap it in an iframe or traditional framing on/from their main site

thus their contact details and static contact would have 100% uptime and the app/dynamic-content or whatever would just be down when their DSL is

so effectively achieving the dual site without dns updates during downtime* {and obviously no delay due to DNS propagation/caching in recovery after downtime*}

* downtime meaning actual disconnected time and times when response is effectively to slow to be useable due to influx of spam, overloaded line due to users running bad-applications {p2p/skype/etc DDOS ing yourself} surge of site visitors, human+bot 

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