Question : What's netmask ?

1.   I run "netstat -rn" command , but cannot see which netmask it is ? How to see the netmask ?or which command can tell me ?

2.   Suppose,When I use "route add -net 10.1.0.0 -gateway 203.155.0.1". What is the netmask of 10.1.0.0 in this case ?

Answer : What's netmask ?

Yes, netmasks are only applied on addresses on your interfaces.
Thats why some one can a package to 203.1.155. 76 and
which net it will got to is determined by your configuration of netmasks and internal routing.

HTH