- 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 address 127.0.0.0 (a class A network). It is used for traffic local to the computer and does not involve any real network hardware or access physical networks. It is often called "loopback address". A computer may have many IP addresses at the same time; therefore, it typically has the 127.0.0.0 loopback address, as well as another IP address which is individually assigned.
5.5.3 I have problems configuring my ppp dial out
GUI. If I were you, I would install kde and use kppp. kppp is really easy to configure and run. To set up your ppp dial out, run kppp (it is under the "K" menu "Internet, or you can run it from the xterm by typing kppp), press the "setup" button, create an account, and fill out the information required: telephone number, authentication protocol, and your Internet Service Provider's (ISP) domain name and the Domain Name Server (DNS) number of your ISP. All this information should have been provided to you by your ISP.
Next, I check if a device called /dev/modem exists and points to the right port. If necessary, I create it by symbolically linking it to the device /dev/ttyS1 (as root):
ls -l /dev/modem
ln -s /dev/ttyS1 /dev/modem
ttyS1 should work if your modem is on the port that DOS calls COM2. Use ttyS0 for COM1 and ttyS2 for COM3 and ttyS3 for COM4. The modem will not dial at all if a wrong port is chosen. For non-standard serial port setups, see the command setserial.
With old versions of kppp, you may get an error message complaining about a "lock". The solution then is to make sure that the file /etc/ppp/options is empty by editing it (as root):
pico /etc/ppp/options
and deleting the word "lock", then saving the file. This problem does not exist in the more recent versions of kppp.
RedHat 6.0 required one additional step: setting the "suid" ("substitute user id") so that "kppp" runs with the effective user id of root (because it needs to access hardware directly). Without it, kppp complains that "it was not properly set up" and "can't create lock file". This has to be done as root:
cd /usr/bin/
chmod a+s kppp
Troubleshooting. If your modem refuses to dial on the port that you are positive is chosen properly, maybe the modem is not set up properly (or maybe it is a "winmodem"? Then throw it away and buy a proper modem).
For example, in one instance, I had to run kppp setup, edit the "modem commands" and input ATZ1 as the "initialization string" (instead of the default ATZ for a standard Hayes-compatible modem). This
