• PC.
• LDP HOWTO Index, section 4.4 : categorized list of HOWTOs about general networking, protocols, dial-up, DNS, VPNs, bridging, routinfg, security and more.
  
• The /usr/share/doc/iproute-<version>ip-cref.ps file, viewable with for instance gv .
  

10.1.2.4. Network interface names

On a Linux machine, the device name lo or the local loop is linked with the internal 127.0.0.1 address. The computer will have a hard time making your applications work if this device is not present; it is always there, even on computers which are not networked.

The first ethernet device, eth0 in the case of a standard network interface card, points to your local LAN IP address. Normal client machines only have one network interface card. Routers, connecting networks together, have one network device for each network they serve.

If you use a modem to connect to the Internet, your network device will probably be named ppp0 . This is normally also the case for connections using a cable modem.

There are many more names, for instance for Virtual Private Network interfaces (VPNs), and multiple interfaces can be active simultaneously, so that the output of the ifconfig or ip commands might become quite extensive when no options are used. Even multiple interfaces of the same type can be active. In that case, they are numbered sequentially: the first will get the number 0, the second will get a suffix of 1, the third will get 2, and so on. This is the case on many application servers, on machines which have a failover configuration, on routers, firewalls and many more.

10.1.2.5. Your host configuration

Apart from the ip command for displaying the network configuration, there's the common netstat command which has a lot of options and is generally useful on any UNIX system.

Routing information can be displayed with the -nr option to the netstat command:

   

bob:~>netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 192.168.42.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo 0.0.0.0 192.168.42.1 0.0.0.0 UG 40 0 0 eth0
This is a typical client machine in an IP network. It only has one network device, eth0 . The lo interface is the local loop.

When this machine tries to contact a host that is on another network than its own, indicated by the line starting with 0.0.0.0, it will send the connection requests to the machine (router) with IP address 192.168.42.1, and it will use its primary interface, eth0, to do this.

Hosts that are on the same network, the line starting with 192.168.42.0, will also be contacted through the primary network interface, but no router is necessary, the data are just put on the network.

Machines can have much more complicated routing tables than this one, with lots of different "Destination-Gateway" pairs to connect to different networks. If you have the occasion to connect to an application server, for instance at work, it is most educating to check the routing information.

10.1.2.6. Other hosts

An impressive amount of tools is focused on network management and remote administration of Linux machines. Your local Linux software mirror will offer plenty of those. It would lead us too far to discuss them in this document, so please refer to the program-specific documentation.

We will only discuss some common UNIX/Linux text tools in this section.

To display information on hosts or domains, use the host command:

   

[emmy@pc10 emmy]$host www.eunet.be www.eunet.be. has address 193.74.208.177[emmy@pc10 emmy]$host -t any eunet.be eunet.be. SOA dns.eunet.be. hostmaster.Belgium.EU.net.2002021300 28800 7200 604800 86400 eunet.be. mail is handled by 50 pophost.eunet.be. eunet.be. name server