361Chapter 12Running Yellow (Freelance web design) Dog Linux IP Address A four-octet number
361Chapter 12Running Yellow Dog Linux IP Address A four-octet number that uniquely identifies your com- puter address. Your system will have a unique IP on your LAN or WAN(wide area network) connection. Netmask Identifies the Host and network portions of the IP address. Aclass A network is 255.0.0.0, a class B is 255.255.0.0, and a class C is255.255.255.0 by default (if no subnet masking is in place). Click OK and, if you aren t using DHCP, set your hostname by selectingHostname.Manually. This can be any name you want to represent your computer. If this is a server, follow your company s naming convention. If youprefer to have DHCP set your hostname, select the Automatically via DHCPradio button. The last options are grayed out if you have selected DHCP. If you chose tomanually configure your network options, enter the following: Gateway IP address The IP address of the machine that is the gatewayor router between your network and the outside networks. For instance, 192.168.1.1 might be your gateway if you have a Linksys or D-Link routerbetween your computer and your cable or DSL connection. Primary, secondary, and tertiary DNS The server that your systemuses for address name translation (converting a hostname into an IPaddress). Your ISP usually gives you this information. 10.Configure the firewall. A firewall acts as a conduit between your computer andother computers that request access to the services it is providing. If you areconnected to the Internet or other networks, enable your firewall. Even if youare not connected to an untrusted network, you should enable the firewall incase you connect at a later date. Two choices are available in this section: No firewall Don t choose this option because it does not checkagainst requests for services. Even if your system is not currently pro- viding services, it s best to not select this option (things can change asthe system grows). Enable firewall The preferred selection. It provides a modicum ofsecurity against malicious entities that may want to attack your systems. Only the default services are allowed at this level, and you can configureaccess for more services as needed. Some of the defaults are: Remote login (SSH).An encrypted protocol that replaces the vulnerabletelnet protocol. With SSH you can log in to the system with an interactiveshell, as well as securely transfer files interactively (SFTP) or noninterac- tively (SCP). For more information on this, type man sshat the commandline after installation. When SSH is unchecked, you can still use these utilities on outgoing connections. This only controls incoming requests from outside your computer. If you need toaccess your system remotely, you can choose this, but it is best to leave it uncheckedfor security reasons. The same applies to the other options presented. Note19_