Make sure the Netscaler has a correct  Subnet IP Addresses ( SNIP ) IP Address that can ping the DNS server , pinging from the Netscaler IP wont work 

Configuring Subnet IP Addresses (SNIPs) | Networking (citrix.com)

Run the following command to send continuous ping packets with the default data size from a source IP address 10.251.03.59, which is a Subnet IP (SNIP) address of the NetScaler appliance:

root@ns# ping -S 10.251.30.59 10.251.30.105