Cidr - Hirschmann Power MICE User Manual

Routing - Basics

2.2 CIDR

The original class allocation of the IP addresses only planned for three ad-
dress classes to be used by the users (see "Basics of IP Parameters" in the
basic configuration of the user manual).
Since 1992, five classes of IP address have been defined in the RFC 1340.
Class Network part
A 1 byte
B 2 bytes
C 3 bytes
D
E
Table 2: IP address classes
Class C with a maximum of 254 addresses was too small, and class B with
a maximum of 65534 addresses was too large for most users, as they would
never require so many addresses. This resulted in ineffective usage of the
class B addresses available.
Class D contains reserved multicast addresses. Class E is reserved for ex-
perimental purposes. A gateway not participating in these experiments ig-
nores datagrams with this destination address.
The Classless Inter-Domain Routing (CIDR) provides a solution to these
problems. The CIDR overcomes these class boundaries and supports class-
less address ranges.
With CIDR, you enter the number of bits that designate the IP address range.
You represent the IP address range in binary form and count the mask bits
that designate the network mask. The network mask indicates the number of
bits that are identical for all IP addresses, the network part, in a given address
range. Example:
Routing L3E
Release 4.2 08/08
Host part Address range
3 bytes 1.0.0.0 to 126.255.255.255
2 bytes 128.0.0.0 to 191.255.255.255
1 byte 192.0.0.0 to 223.255.255.255
224.0.0.0 to 239.255.255.255
240.0.0.0 to 255.255.255.255
2.2 CIDR
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