[lug] ip address bouncing

[Hugh Brown]

"Nate Duehr"
> 
> Thoughts below...
> 
> On Mon, Oct 22, 2001 at 09:43:45AM -0400, Hugh Brown wrote:
> > We are having a weekend long power outage where I work and I need to move a
> > box to another location.  I am trying to minimize the amount of time it
> > takes for dns to update.  
> 
> Bummer.  Need to move your computers to a data center!  :-)  (Blatant
> plug for my employer here.. heh)

DC to CO is a bit more traumatic a move than a mile down the road :)

> 
> Minimizing DNS downtime is a direct relation to turning your TTL time
> down at least 2*TTL in advance.  If your DNS TTL time is longer than a
> week, you're already hosed if the outage is planned for this coming
> weekend.
> 
> > Is it possible to take the old ip address and redirect all traffic destined
> > to it to a different address?
> 
> Only if something is still answering on the old IP address.

I am doing the move on wednesday evening. so I have all day thursday and
friday to have something answering on the old ip address.

How is this traffic redirect done?

> 
> > If a have two A records for a host and the first ip isn't available will
> > the second ip be tried or will the process return a host not
> > found/unavailabe?
> 
> Multiple A-records officially are handled however the resolver wants to
> handle them.  In practice, they round-robin.  So by adding another A
> record with another IP, 50% of the people coming to your site will get a
> failure on the first try, and have a 50/50 chance of hitting the "up"
> site every time they hit refresh.  There's a rather large warning
> against using DNS for load-balancing in the DNS FAQ at www.isc.org --
> and this is why.

That's what I thought.  Just wanted to be sure.

> 
> I recommend you get your TTL time turned down immediately, and get
> another "mirror" server ready to handle ALL your traffic at another site
> so you can just point your DNS there during your downtime.  That's the
> cleanest way to do it.  Also, don't forget to consider where your DNS is
> hosted.  If it's hosted at the site that is going down and there's no
> off-site slave configuration you'll have an awfully hard time getting
> anyone to your site at all.

I turned it down to an hour from two days so I might be able to manage it.

One of the authoritative hosts for the domain is offsite so I should
hopefully be okay.  We'll see how it all turns out.  Worse comes to worse,
we tell people to point at an ip address.

Thanks much for the help.

Hugh