Specifications
hg-c.fm
A31003-H3580-M103-2-76A9, 01-2009
HiPath 3000/5000 V8 - HG 1500 V8, Administrator Documentation
C-15
Nur für den internen Gebrauch
WAN/LAN Management
IP Addressing: Subnets
C.2 IP Addressing: Subnets
To circumvent the scarcity of official IP addresses and to divide an IP network into separate
sub-networks, the "sub-netting" procedure can be used.
For the allocation of official IP addresses, for example, sub-netting makes it possible to gener-
ate additional independent IP networks by using existing Class A, B and C network addresses.
Various classes and standard network masks have been agreed upon for networks:
Division into independent subnets also offers the considerable advantage that local network
traffic remains in its own subnet. Access to third-party networks is only possible via a router.
The basic functionality of sub-netting is relatively simple and is based on the "netmask". This
mask is used for defining bits which represent either the network or the host segment within an
IP address. Set bits (1) represent the network segment, while deleted bits (0) represent the host
segment.
The best way to analyze a netmask is in binary format. The Class C standard netmask
"255.255.255.0" is a good example.
In netmask "255.255.255.0", the first 3 bytes represent the network segment (all bits 1) and the
last byte represents the host segment (all bits 0).
The host (router, workstation, etc.) uses this netmask to determine whether the IP address be-
ing addressed is located in the local network. If the destination host is not located in the same
network, packets are forwarded to this address via suitably defined routing mechanisms.
To create customized subnets, you will first need to determine the number of sub-networks to
be established within a class-based network (Class A, B, C). When a network is divided, 2
n
sub-
nets are always created as a result. An example will illustrate this more clearly.
Class Netmask
A 255.0.0.0
B 255.255.0.0
C 255.255.255.0
Table D-1 Network Classes and Standard Network Masks
Network Host
Bytes 1st byte 2nd byte 3rd byte 4th byte
Netmask 255 255 255 0
Binary format 1111 1111 1111 1111 1111 1111 0000 0000
Table D-2 Example of a Class C Standard Network Mask