Network Information: Dynamic and Static

If you are on a network, you may need to obtain certain information to configure your interface. Most networks now support dynamic configuration using the Dynamic Host Configuration Protocol (DHCP). In this case, you need only check the DHCP entry in most network configuration tools. However, if your network does not support DHCP, you will have to provide detailed information about your connection. Such connections are known as static connections, whereas DCHP connections are dynamic. In a static connection, you need to manually enter your connection information such as your IP address and DNS servers, whereas in a dynamic connection, this information is automatically provided to your system by a DHCP server when you connect to the network. A DHCP client on each host will obtain the information from a DHCP server serving that network.

In addition, if you are using a DSL, ISDN, or modem connection, you will also have to supply provider, login, and password information, whether your system is dynamic or static. You may also need to supply specialized information such as DSL or modem compression methods, dialup number, or wireless channels to select.

You can obtain most of your static network information from your network administrator or from your ISP (Internet service provider). You would need the following information:

• The device name for your network interface   For LAN and wireless connections, this is usually an Ethernet card with the name eth0 or eth1. For a modem, DSL, or ISDN connection, this is a PPP device named ppp0 (ippp0 for ISDN). Virtual private network (VPN) connections are also supported with Crypto IP Encapsulation devices named cipcb.

• Hostname   Your computer will be identified by this name on the Internet. Do not use localhost; that name is reserved for special use by your system. The name of the host should be a simple word, which can include numbers, but not punctuation such as periods and backslashes. The hostname includes both the name of the host and its domain. For example, a hostname for a machine could be turtle, whose domain is mytrek.com, giving it a hostname of turtle.mytrek.com.

• Domain name   This is the name of your network.

• The Internet Protocol (IP) address assigned to your machine   This is needed only for static Internet connections. Dynamic connections use the DHCP protocol to automatically assign an IP address for you. Every host on the Internet is assigned an IP address. Traditionally, this address used an IPv4 format consisting of a set of four numbers, separated by periods, which uniquely identifies a single location on the Internet, allowing information from other locations to reach that computer. Networks are now converting to the new IP protocol version 6, IPv6, which uses a new format with a much more complex numbering sequence (see Chapter 38).

• Your network IP address   Static connections only. This address is usually similar to the IP address, but with one or more zeros at the end.

• The netmask   Static connections only. This is usually 255.255.255.0 for most networks. If, however, you are part of a large network, check with your network administrator or ISP.

• The broadcast address for your network, if available (optional)   Static connections only. Usually, your broadcast address is the same as your IP address with the number 255 added at the end.

• The IP address of your network's gateway computer   Static connections only. This is the computer that connects your local network to a larger one like the Internet.

• Name servers   Static connections only. The IP address of the name servers your network uses. These enable the use of URLs.

• NIS domain and IP address for an NIS server   Necessary if your network uses an NIS server (optional).

• Login and password information   Needed for DSL, ISDN, and modem connections.