f5 gtm update check --no response from update server

i have f5 gtm standalone and when i goto software management and press check now it give error --no response from update server and i checked the firewall it working fine and tried nslookup from f5 appliance it working fine also i checked with telnet and woring fine " Trying 104.219.110.134... Connected to .

 

Escape character is '^]'.

Trying 104.219.111.132... Connected to . Escape character is '^]'.

 

any help please