3.1.3 Addresses: IP, Broadcast, Netmask, ...

If you're about to hook your machine up to your company's, school's or university's network (i.e. most probably the real Internet :), go to your local network-administrator and get the following informations:

• your IP-Number
• your host's name, including domain.
• Netmask
• Broadcast-address
• Defaultrouter (IP-number)
• Nameserver (primary and secondary)
• the protocol to use, SLIP or PPP

If you're about to use SLIP or PPP, possibly via a telephone line, you'll probably need the following informations:

• Phone-number of your terminal-server
• Account, password etc. to get access to your terminal-server
• IP-number(s) of the terminal-server's dial-ins
• Whether your provider offers PPP or SLIP, and how to start it

If you just want to run your own little LAN at home, you can choose your own values for most of the things above:

IP-number:

Choose an IP-number from either class B or C. As you're isolated from the internet, it doesn't really matter what address(es) you choose, as long as they are valid addresses (see section 2.2 TCP/IP address format). If you choose a couple of addresses, please pay attention that they are all in the same (sub)net! (see section 2.3 Subnetting and Routing)

Hostname:

Any valid hostname you like, see section 2.4 Name service concepts. You'd better not choose a domainname because you'll only have to type longer hostnames (and believe me, you'll have to type those hostnames quite some times during tuning your network! :-).

Netmask:

Determine this one according to the rules from section 2.2 TCP/IP address format. As you surely don't want to invent subnets, the netmask goes hand in hand with the IP-number(s) you choose.

Broadcast-address:

If there's no 4.2BSD-system on your network, determine your broadcast-address after the rules stated in section 2.2 TCP/IP address format, i.e. set all host-bits to "1". If you've got one or more 4.2BSD-systems on your network, you've to pay attention to set the right broadcast-address, as 4.2BSD has a bug in its networking code, concerning the broadcast address. This bug forces you to set all host-bits in the broadcast-address to "0"!!!

Defaultrouter:

Most probably not needed at home.

Nameserver:

You don't need this for the first steps, and most probably you won't set up DNS at home. See section 2.4.2 The Domain Name Service (DNS), for some details.

To illustrate this, I'll give you two examples.

Example 1: DUSK at the university's network

• IP-number: 132.199.15.99
• Netmask: 255.255.255.0
• Broadcast: 132.199.15.255
• Name: DUSK.RZ.UNI-REGENSBURG.DE
• Defaultrouter: 132.199.15.1 (RZI.RZ.UNI-REGENSBURG.DE)
• Nameserver(1): 132.199.1.2
• Nameserver(2): 132.199.1.1

I got all these values from the local network admin. As the system is connected to the internet, I use the University of Regensburg's class C network (132.199.0.0) and their domainname (UNI-REGENSBURG.DE).

Example 2: DUSK & NOON at home

• DUSK:
  • IP-number: 132.199.15.98
  • Broadcast: 132.199.15.255
  • Name: DUSK
• noon:
  • IP-number: 132.199.15.97
  • Broadcast: 132.199.15.255
  • Name: NOON

I used the second setup at home, with no connection to the internet. Therefore, I have chosen neither domainname nor defaultrouter or nameserver. (I choose those IP-numbers for the case that I'm going to hook up noon to the net, just for fun :-).