We plan to have ISP level redundancy. Our webserver as www.xyz.com is published by address as A.B.C.D. Here users are using ISP DNS to resolve the name to ip adress. No we plan to have ISP2 as redundant to ISP 1. So we plan to host GSS ( Global site selector ) in our data center and host DNS on it. So ISP DNS will forward the DNS request to our GSS as a recursive query on port 53.
This query will come from ISP1 as well as ISP2. If ISP1 link is down it will come from ISP2 link , as both IP address will be configured in our ISP DNS. ( i really doubt if this works ). But if it works then when ISP1 link is down GSS will receive a query on port 53 from ISP2 link. In this case it should resolve the IP as P.Q.R.S which is routed by ISP2 and answer the user query with this IP address. So that user will be able to visit URL www.xyz.com from ISP2 link. Attaching PPT slide.
Please check the validity of this design. Mainly can ISP DNS forward the query to second IP address which is reachable by ISP2 link. ( when ISP1 link goes down )
Any configuration example on cisco.com.
Please see slide attached.
Thanks in advance