DNS Server unknown in Network access

Hi We are using F5 LTM and APM modules. We have created a network access to built a tunnel and access the applications via tunnel(such as SAP application using SAP logon pad). We have chosen the traffic options as split tunnel, and we have added the Ip's individually with subnet and added dns suffix in DNS addres space. We have added the primary and secondary DNS servers in DNS/HOST. While trying to access the application the VPN tunnel is built but we are getting error as hostname unknown. When we check with command prompt the tunnel is built with the lease pool IP we have mentioned but when we try nslookup we are getting dns server unknown. Please help thanks!