ZXR10 8900 Series User Manual (Basic Configuration Volume)
Class
Prefix
Characteristic
Bit
Network
Bit
Host Bit
Range
Class
D
1110
Multicast address
224.0.0.0 to
239.255.255.255
Class E
1111
Reserved
240.0.0.0 to
255.255.255.255
Some addresses of Class A, B and C are reserved for private net-
works. It is recommended that the internal network should use
the private network address. They are:
�
Class A: 10.0.0.0 to 10.255.255.255
�
Class B: 172.16.0.0 to 172.31.255.255
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Class C: 192.168.0.0 to 192.168.255.255
This address classification method is to facilitate routing protocol
designing. From this method it can be known the network type just
by the prefix characteristic bit of the IP address. This method,
however, cannot make the best of the address space. With the
dramatic expansion of Internet, problem of address shortage be-
comes increasingly serious.
Network, Subnet
and Host Bit
To make most of IP addresses, network can be divided into multiple
subnets. Borrow some bits from the highest bit of the host bit
as the subnet bit. Remaining part of the host bit still serves as
the host bit. IP address is composed of three parts: network bit,
subnet bit and host bit.
Network bit and subnet bit identify a network uniquely. Subnet
mask is used to decide which parts of IP address are the network
bits, subnet bit and host bit. The part with the subnet mask being
1 corresponds to the network bit and subnet bit of the IP address.
Part with the subnet mask being 0 corresponds to the host bit.
Division of the subnet greatly improves the utilization of the IP
address, and alleviates the problem of IP address shortage.
Some conventions for IP addresses:
�
0.0.0.0 is used when the host without an IP address is started.
Address is obtained through
RARP
,
BOOTP
and DHCP. This ad-
dress is also used as a default route in the routing table.
�
255.255.255.255 is used for the destination address of broad-
cast and cannot be used as a source address.
�
127.X.X.X is called loop-back address. When the actual IP ad-
dress of the host is not known, this address is used to represent
“this host”.
�
Address with only the host bit being 0 indicates the network it-
self. Address with the host bit being 1 is the broadcast address
of the network.
�
Network part or the host part of a valid host IP address cannot
be all 0 or 1.
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