Managing an Internet outage

Mike Diggins diggins at
Sun May 11 23:26:31 UTC 2008

On Sun, 11 May 2008, Damien Hull wrote:

> Why not go with a master and slave DNS configuration? This is the way DNS should work.
> 1. The master DNS server is the one that updates all the other DNS servers
> 2. The save gets it's info from the master
> 3. Any changes on the master get pushed or pulled to the slave DNS servers
> 4. Place your save DNS servers off site
> If your internet connection goes down you don't need to do anything to 
> the slave DNS server. It's got the correct info.
> I'm assuming you have a backup email server off site as well. Assuming 
> your MX records are correct the backup email server will start receiving 
> email.
> Your website won't be available while your internet connection is down 
> but I don't see that as a big deal. Unless you are providing something 
> critical.
> When your internet connection comes back you will start receiving email 
> and your website will be available. Any email that was on the backup 
> email server will be delivered to your main email server.
> This is the way things should be configured.

Thanks for the replies. This is what we have already, except for the off 
site DNS server. The point of the project is to provide a web based 
notification to off site customers that we're down (working on the 
problem, ETR, etc). The web server for that will be located off campus as 


> ----- Original Message -----
> From: "Dawn Connelly" <dawn.connelly at>
> To: "Mike Diggins" <diggins at>
> Cc: comp-protocols-dns-bind at
> Sent: Sunday, May 11, 2008 12:46:52 PM GMT -09:00 Alaska
> Subject: Re: Managing an Internet outage
> Best practice is to always make sure that your authoritative DNS servers are
> on physically different networks so your boss is right in thinking this
> needs to happen. Couple things to consider. If your master DNS server is
> down, you'll need to reconfigure the offsite machine to be primary so you
> can change the DNS resolution. Not a big deal but make sure to include that
> step in your DR plan. You have control over your TTLs. You can drop them to
> 10 minutes (or whatever your SLAs dictate) in the event of a network outage
> so you can recover faster but not always have the increased load. Mail will
> queue on the email servers that are trying to send it for awhile if it can't
> contact your mail server so that buys you some time too. You might want to
> leave your MX resolution to the correct machine IP address even in your
> failure state to make sure that mail queues on the remote end and to make
> sure it sends as soon as the network is back up. It would be better if you
> had an email server as your DR site with a higher weight though from a best
> practice stand point. Also some ISPs tend to just cache one authoritative
> DNS server and continually try to hit it over and over even if it's down.
> The only thing you can do to fix that is ask the ISP to clear their cache.
> Road Runner has burned me with that multiple times.
> So your DR plan would look something like this:
> Network outage is detected.
> Stand-by named.conf file swapped on offsite machine to reference outage zone
> files and configure machine as master
> Outage zone files include the following records:
> @ 600 IN A <IP address of "We are broken" webserver>
> @ 3600 IN MX 10 <IP address of email server>
> * 600 IN A <IP address of "We are broken" webserver>
> Once failure has been cleared, stand-by named.conf is swapped back with
> original file and named is restarted.
> You can script this to happen automatically if you have a monitoring system
> in place with some peril scripts or you can do it manually. You can also
> look at products that do all of this for you automagically. The Global
> Traffic Manager by F5 (Big-IP GTM) is the one I'm most familiar with but I'm
> sure other's on this list could give other examples too. The GTM box will
> continually test access to your resources and as soon as they become
> unavailable they will hand out whatever information you have configured as
> your fallback IP address.
> On Sun, May 11, 2008 at 12:31 PM, Mike Diggins <diggins at> wrote:
>> We occasionally have a situation where our Internet access is completely
>> down. My Manager has asked about the viability of locating a DNS server
>> off site, and during a situation when we're down, modifying it so that it
>> resolves my entire domain to a single IP address. Web users would be
>> redirected to that address, and a web page would explain we're off line.
>> Our DNS TTL is set to 1 hour, however, I'm concerned that sites might
>> cache that address for longer than the TTL, and affect things such as mail
>> delivery beyond the outage. Does anyone have an opinion on this plan?
>> Obviously improving our redundancy is a better solution, and that will
>> come in time. Right now this seems like a quick and easy (dirty) solution.
>> -Mike

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