hello gurus

[Kevin Darcy]

Graham Dinning wrote:

> HI there people.
>
> A few questions
>
> 1) I am setting up a server right now on a new sub class C network and
> need some guru guidance about DNS. Assume the following :-
>
> All masks mask 255.255.255.192
>
> www.firstdomain.com
> ip xxx.xxx.xxx.193   eth0
> www.seconddomain.com
> ip xxx.xxx.xxx.194   eth0
> www.thirddomain.com
> ip xxx.xxx.xxx.195   eth0
> www.forthdomain.com
> ip xxx.xxx.xxx.196   eth0
> www.fifthdomain.com
> ip xxx.xxx.xxx.197   eth0
>
> New server
>
> www.firstdomain.com
> ip yyy.yyy.yyy.193   eth0
> www.seconddomain.com
> ip yyy.yyy.yyy.194   eth0
> www.thirddomain.com
> ip yyy.yyy.yyy.195   eth0
> www.forthdomain.com
> ip yyy.yyy.yyy.196   eth0
> www.fifthdomain.com
> ip yyy.yyy.yyy.197   eth0
>
> Pick one domain SAY www.firstdomain.com.
>
> How can I set up the DNS records to say
>
> www.firstdomain.com TRY yyy.yyy.yyy.193 first and if no luck try
> xxx.xxx.xxx.193.
>
> Is it similar to the MX record priority scheme?
> Is it possible in the first place?
>
> We have a few businesses that need their web sites going 18/7.
> I am trying to figure this out so that there is very little down time if
> possible.

Basically, because of caching, there is currently no good way to provide
address failover in DNS alone. Maybe some day all browsers will support the
SRV record type, but AFAIK so far none of them do. Until then, you're stuck
buying expensive load-balancing devices (some Telecom vendors can sell you
those) to do this job, or not doing failover at all.

(Note: I'm assuming that these are Internet websites, or that you don't
control all of the nameservers that the clients (or their proxies) will use
to resolve the website names. In limited circumstances, where you control
every single one of the nameservers involved, you could configure all of
them with the "rrset-order" or "sortlist" options of BIND to hand out
addresses in a particular order. Even so, not all browsers implement
address failover, or if they implement it at all, they implement it poorly,
e.g. with unacceptably-long timeouts between successive addresses).


- Kevin