telnet name_of_the_machine_you_are_sitting_at
After a successful login, you can exit the telnet session by typing
exit
Finally, try to telnet another computer on your network:
telnet name_of_a_remote_machine
If this works on all machines, your eth0 network interface is set up.
After setting up your ppp and connecting to your Internet Service Provider (ISP), you will have another network interface (ppp0) and then will be able to telnet any machine in the world.
Here is a summary of the meaning of IP numbers.
The IP number (sometime called "IP address") is split into four groups of numbers separated by dots. E.g., 123.123.123.123 is a fromally-valid IP number. (All numbers here are shown in their decimal representations.) Within each group of numbers, the value may range from 0 to 255 (8 bits). The group of numbers from dot to dot is often referred to as an "octet" because it has 8 digits in its binary representation. The address contains a "network number" followed by "host number" (a host is an individual computer within a network). The network may be denoted by one, two, or three octets. The host is the trailing balance of the IP number (three, two, or one octet, respectively).
When the host number is filled with zeros (in all octets that denote the host), the resulting IP number is interpreted as referring to this host (therefore, the number is called "the network number"). When the host number is filled with 255 (in all the octets), the IP address is interpreted as all hosts on the network (and called "the broadcast address"). When the network number is filled with zeros (in all the octets that denote the network), it is interpreted as referring to this network. If the network number is filled with 255 (in all its octets), it refers to all networks.
Networks are divided into 6 classes. The most important are class A, B, and C.
Class A networks. Class A networks are networks with numbers between 1.0.0.0 and 127.0.0.0. The network number is contained in the first octet. The host number is contained in the trailing three octets. This division results in 127 big networks, each of which may contain up to about 1.6 million hosts.
Class B networks. Class B neworks are networks with IP numbers between 128.0.0.0 and 191.255.0.0. The network number is contained in the first two octets. The host number is contained in the trailing two octets. This gives 16320 networks, each of which may contain up to 65024 hosts.
Class C networks. Class C networks are networks with IP numbers between 192.0.0.0 and 223.255.255.0. The network number is contained in the first three octets. The host number is contained in the last octet. This results in nearly 2 million networks, each of which may contain up to 254 hosts.
Classes D, E, and F. These networks have addresses in the range from 224.0.0.0 to 254.0.0.0 and are either experimental, or are reserved for future use. They do not specify any network.
Private address spaces. The following IP number ranges are reserved for private internets:
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
From among these, an IP number is selected for a network which is behind firewall (or which has no connection to the world-wide web). The balance of the valid IP addresses are registered and resolved by a DNS server.
Default route. This is a special IP address 0.0.0.0. It is used to mark the default network interface i.e., the hardware to which the traffic will go on default. For example, the default route may be assigned to eth0 (the symbolic name for the first ethernet card) or eth1 (the second ethernet card), or ppp0 (the first point-to-point modem connection), etc.
Local host. This is a special IP
