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SDB:Purpose and practical instruction to use IP addresses
A network has to be installed. Therefore IP addresses are needed.
IP addresses are quite analogous to telephone numbers. Their destination is to identify certain devices, resembling to telephone sets and to enable to dial them up. Analogous to a human beeing, a computer can own none, one or multiple network devices.
The analogue to telephone is much more far-reaching, resembling to the area code network addresses exist. Short area codes correspond to large networks, long area codes correspond to small networks. A significant difference between telephone numbers and IP addresses is the fixed length of all IP addresses. All IP addresses of the current standard have a fixed length of 4 Bytes. They are displayed for convenience as decimal numbers, where every cipher, corresponding to a byte is seperated to the next one by a dot. Examples are:
All those examples are strictly interdicted in self made configurations, and only allowed, if the consequences of their use is very well known.
- 0.0.0.0 is the first educible address and serves to set the default route
- 127.0.0.0 is the loopback network
- 255.255.255.255 is the last representable address and is not in use yet.
Two different computers must not have the same IP address, as two telephone subscribers must not have the same telephone number. To obtain IP addresses without announcement and approvement, three categories of networks are reserved for private use only. They are
- 10.0.0.0 (1 net with 16777214 members)
- 172.16.0.0 until 172.31.255.255 (16 nets with 65534 members each)
- 192.168.0.0 until 192.168.255.255 (256 nets with 254 members each)
All IP addresses have the same length and are similar functionally, therefore something like a area code/subscriber number discrimination is necessary. This discrimination between area code look-alike and subscriber number look-alike is done by the so-called netmask wich reports the designation, the area code is bit by bit set to one, the subscriber number is bit by bit represented by zeroes.
Customarily, the addresses
- from 0.0.0.0 to 127.255.255.255 use netmask 255.0.0.0, called A class net
- from 126.96.36.199 to 188.8.131.52 use netmask 255.255.0.0, called B class nets and
- from 192.0.0.0 to 184.108.40.206 use netmask 255.255.255.0, called C class nets.
In contrast to the classical telephone operation, no flash or ground key is available in the networking environment. To do something like an operator or local telephone switch call, two addresses are reserved, the first and the last in a network. They cannot be commonly used. For example, in net 192.168.33 the addresses 192.168.33.0 (network address, operator call) and 192.168.33.255 (broadcast address, message for all members of that network) are dedicated to that special purpose.
Special attention is to be payed on computers, which own more than one network device, for example a computer with a classical Ethernet card and a modem or ISDN-card. To use telephony allegory, it is member of two different areas. Accordingly, the area codes must differ. If its Ethernet address is 192.168.33.57, it is member of net 192.168.33, and the modem or the ISDN-card respectively must have an address like 192.168.97.28, to be in network 192.168.97.
While using IP based modem connections, special care is to be taken of the use of statical allocated IP addresses (rather rare and often a fee is demanded) or the use of dynamical allocated IP addresses. With statical allocated IP addresses the directions of the provider are to be followed thoroughly. In the case of dynamically allocated IP addresses, the addresses must be taken from one of the above mentioned ranges for private use, preferably the 192.168 A class are used. Never take for the IP address of the dial-in-server the address of the name-server. The best method to select an address is to select an address in the same network as the modem, e.g.:
- 192.168.1.1 for the own modem (or ISDN card)
- 192.168.1.2 for the dial-in-server of the Internet provider
IP addresses are allocated with the configuration program YaST2 to every special network device. YaST2 make proposals for the netmask according to network type, which can be adopted in most cases. YaST2 tabulates the IP addresses of the network devices. This table should be used to compare the network numbers of the devices to avoid interferences.
As IP addresses correspond to telephone numbers, there is a correspondence to the telephone directory service. The inquiry service corresponds to the locally operating DNS (Domain Name Service) or BIND (Berkeley Internet Name Domain), the international inquiry service, which reports numbers not located in the local telephone system, corresponds to the forwarders entries which give the access to superior super-name-servers. Like the number of the inquiry service is needed, the computer needs to get a name-server-entry. This entry is made with YaST2.
The name service assigns symbolic addresses, e.g. www.suse.com to logical addresses, IP numbers, e.g. 220.127.116.11. The assignment of logical addresses, the IP addresses to physical addresses, the real network devices will be configured using YaST2. In the telephony analogue YaST2 is the tool to do the wiring.