Networks; Network Addresses And Subnet Masks - HP ProCurve 7000dl Series Basic Management And Configuration Manual

IP Routing—Configuring Static Routes
Overview
11-4
Unlike MAC addresses, IP addresses are not permanent or hardware specific.
A host can change its address, and it can receive a temporary address from a
server. However, public IP addresses must be unique and globally significant.
(Otherwise, hosts could never be certain that data would arrive at the desti-
nation they intended.) Certain IP addresses are reserved for private networks;
these addresses are locally significant and can be used by any number of
different private organizations.

Networks

A network is a group of hosts that share a network address. Traffic between
these hosts can be forwarded by bridges or switches. However, when a packet
must be sent into a new network—that is, when its source and destination
have different network addresses—the packet must be routed.

Network Addresses and Subnet Masks

A network address is the first part of a host's IP address. The second part of
the IP address uniquely identifies the host within that network.
A subnet mask defines which bits identify the network and which identify the
individual host. The subnet mask consists of 32 bits—first, a string of contin-
uous ones; then, a string of continuous zeros.
All bits in the IP address that correspond with a one in the subnet mask are
network bits; all bits that correspond with a zero are the host bits. (See
Figure 11-1.)
Networks can be of varying sizes, depending on how many bits are allocated
for the network address and how many for the host address. The greater the
number of network bits, the fewer the addresses the network contains.
(Because most of the bits define the network, there are fewer bits in which to
store different addresses on that network.)
The first address (all zero host bits) in every network is reserved for identifying
the network, and the last address (all one host bits) for broadcasting.