Hello Bhaskar,
We too facing similar problem, We tried kernel upgrade to 721_EXT PL 300 but no luck.
sapgw00 entry is maintained in service file and also host file entry with FQDN is maintained.
I am able to telnet on port 3300, all other functionalities are working perfectly even RFC communication between this and other system (both way) is working fine.
We have restart the sap instance too.
Saurabh