Hi i have two ISP and I want to configure failover between them but problem is that their DNS are different form each other so if one link down then other is not working with pervious DNS.

Plz give me any idea or script so that when ISP change then DNS are also changed or any other idea

fill in the dns of both isp's by dhcp servers

you can also use public DNS servers

I am tackled the same kind of issues lately and DNS is not the hardest worries to tackle. You can put both DNS servers into your local DNS and let the local DHCP to send out both of these to your clients. Or just use your local DNS server.

For me the hardest part is actual detection if the ISP connection is indeed down. For example with my cable ISP the MT bundled functionality is pretty much useless (such as the check-gateway option), because they insist on gateway not pingable as not equal to network being down. Also, my setup has different alternative ISP connection attached physically into different MT boxes and usually several hops away from each other. So, I've had several attempts to script around those issues. Hopefully I am successful, soon.

Use public DNS servers and this solution:
http://wiki.mikrotik.com/wiki/Advanced_ ... _Scripting

HTH,

Hello!
The first workaround is to use public DNS servers such as google DNS (8.8.8.8, 8.8.4.4). May be this one is the best variant to You.
The second is to use particular script to switch DNS settings. Visit my site http://mikrotik911.com/en where You will find a solution to Your problem. If You need create a failover access to the Internet You may find this resource is useful.
Best regards!