Hello frends,
Again I need your help about DNS server.

My question is not any problem but it is just thinking about possiblity.

My Network Scenario is..
We have two isp. All server now working on ISP1 now what happen if ISP1 link goes down our webserver down .Now we have registered domain in ISP2 ip i.e whenever ISP1 link down, my domain resolved by ISP2 ip. Is that possible through dns server?
how can i do for this pls if have any idea pls share with me.

Any reply will be appreciated.

Thank a lot.

I created Network Diagrame in jpeg format. But cant put here.

Of course that is possible just point your dns secondary to second ISP, but i dont see a point in users being able to resolve your hostname when they are not able to connect to you as your link will be down.

I think you should be looking at some kind of link redundancy.

Thank you very much for replyint.

I understand it. But it is possible thourh slave dns server and slave server is point to second isp?. I dont know it is possible or not but it may be work. please say about this.
Thank you.

in general u need a dynamic DNS solution
i'v heared about some DNS provider for these kind of things
one of them is no-ip.com

correct me guys if im wrong....

Yes that is possible but in that case the second server will not be a slave of the master, as it will have different records.

This is not something that DNS alone can do. As pointed out above, your second DNS box is not a slave if it doesn't have identical data to the master. With 2 ISPs, you can create 2 of any record (2 A records, 2 www records), but if ISP 1 goes down, NS2 will still give out ISP 1 addresses 50% of the time, and those will fail.

To get what you are looking for, you'd need to have something that can test each link, and modify your DNS info so that if one link goes down, it only gives out info for the link that is up. You could do it simply by modifying tools like nagios to activate scripts to change the DNS info.

If you need really super availability, you should look at something like http://linux-ha.org/ which is something like a software load balancer. A hardware load balancer is also excellent, but also extremely expensive.

Also, for you to do a "simple" DNS correction, you have to b e sure your network has an architecture that allows it to still function with one link down.

Peace,
JimBass