Netmask is an important concept to understand.

Do you understand the concept of a binary AND operation? If so, the netmask will be easy to grasp.

Think of an IP address as a single large binary number, 32 bits long. We look at it as four separate "octets" of eight bits each, but it's really just a single large 32 bit number.

The netmask allows you to define the range of addresses that counts as a "subnet". In other words, when the unit broadcasts messages, what subset of IP addresses is considered local and worthy of receiving those messages?

The netmask simply gets AND'ed to the ip address. Everything that passes the AND operation is considered part of the subnet.

So if your subnet is the 255 addresses grouped within 123.456.789.xxx, then your netmask would be 255.255.255.0. If your subnet was larger, say the 65,000 address under 123.456.xxx.xxx, then your netmask would be 255.255.0.0. See how that works?

As for the default gateway, you should be able to leave that blank if you don't have one. That's another lesson for another time. (Anyone want to chime in with the Default Gateway lesson?)

___________
Tony Fabris