Question : Can we put 255.255.255.255 as the subnet mask ?

I have seen this configuration anomaly in my Tata-Indicom USB data card, I see
subnet mask is 255.255.255.255 and also IP address and Default gateway is same.


PPP adapter SXC-1080:

        Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : WAN (PPP/SLIP) Interface
        Physical Address. . . . . . . . . : 00-53-45-00-00-00
        Dhcp Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : 121.245.8.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.255
        Default Gateway . . . . . . . . . : 121.245.8.100
        DNS Servers . . . . . . . . . . . : 203.197.12.30
                                            202.54.1.18

Could someone please let me know what is happening here.

Answer : Can we put 255.255.255.255 as the subnet mask ?

This simply means that the network that interface connects you to is a 1-host network, i.e. 121.245.8.100 is the only host and it also happens to be the gateway. As long as the routes are correctly setup and everything is working, there is nothing to worry about.