Backup DNS

Ok I have been reading about DNS and maybe someone can shed some light onto this for me.

I was told the following which I think is not right:

Have domain mydomain.com (lets say)

Have namer sever mydomain.net
Namservers ns1.mydomain.net and ns2.mydomain.net

That points to the IP addresses that the host provided to me.

Now what I want to happen is if ns1 and ns2 are not avail. for whatever reason I want them to fall to another server.

So can I say go to another host create an account for mydomain.com. Get two new nameservers say ns3.mydomain.net and ns4.mydomain.net. Log into my domain registrant and add those nameservers to the DNS of mydomain.net and put up a page on this server that says Please come back soon as we are doing maint. or something like that?

Can DNS fall-over if you will like that?

I know this is not the best explination but if anyone can clerify if this will work or not that would be a big help.

K.

question. Will this "maintanance" page be on the same computer as the website that goes down?

No maybe I can explain it better I have host a and host b. Host A has the real web site on it. If host A's DNS or site goes down I want to display the site that is on Host B.

So yes they are on different machines in different data centers.

There's no way to automatically switch from plan A to plan B if plan A fails. Well, not easily anyway.

Plan A is the data center with your main website and dns server.
Plan B is the data center with your "maintenance" website and backup dns server.

1) One option is to go to your registrar and change the name servers to plan B if plan A is down. There is a downside however. With each change it may take up to 48 hours for the change to take effect. So for switching to plan B then back to plan A can spell out 4 days of downtime. yuck.

2) Possibly the best option is to always use plan B's name servers. Just point the domains to plan A's webserver when it is up. When it is down point the domains to plan B's webserver. It is easier to make this process automatic. You can have a script on plan B's server monitoring the webserver on plan A. If it detects that plan A has gone down, it will then modify the zone file on plan B's name server and reload the zones so that changes take effect. This process is nearly instantaneous with very little downtime - depending on how long you let caching servers cache your domains.