Netmask and subnet mask

[jakemon0709]

Newbie Question: I need to know what our WAN netmask and subnet mask are. Where can I find that information?

[MUHAMMAD SHAHEEN]

Check Serial interface in the config or use show interface command

Shaheen

[jakemon0709]

Does the internet addresss or broadcast address = netmask?

[olorunloba]

The internet address is the ip address of the interface.

The broadcast address is the destination address used by the router for broadcasts out the interface

You mostly likely have gotten the above information from show ip interface command. Instead, try show interface or sh run

For show run, the subnet mask is given after the ip address, in the interface configuration e.g.

interface e0

ip address 1.1.1.1 255.0.0.0

For show interface, it is also given with the ip address but shown in another format i.e.

Internet address is 1.1.1.1/8

where 8 specifies the number of 1s in the subnet mask.

[jakemon0709]

Ok. How do you discover the netmask though?

[olorunloba]

The netmask is the same thing as the subnet mask. If you are referring to the Wildcard mask (often use in the configuration of access-list), for each octet of the subnet mask, subtract it from 255 i.e.

255.255.224.0 becomes 0.0.31.255 and

255.192.0.0 becomes 0.63.255.255