Thank You for your response.
The failover action is working correctly in GTM when I am trying from Internal DNS.But when I am trying to access the URLfrom Public Inernet,it is not giving correct results.
We have used a Private IP as the GTM listener.The traffic flow is External DNS-->NAT in Firewall( Public to Private)--->GTM( self IP/Listener IP- private IP space)---> Wide IP---> Wide IP pool --->Active/DR VIP of LTM.......
I have created an NS record for DNS delegation in External DNS and two "A" record (Pubic IP)for active/DR site, CNAME record for the actual URL. Still, am not able to access the URL in externally.
Awaiting your valuable feedback on this.