What is an IP Network? – InetDaemon’s IT Tutorials

Networks provide communication between computing devices. To communicate properly, all computer (hosts)
on a network need to use the same communication protocols. An Internet Protocol network is a network of computer using Internet Protocol for their communication protocol.

All computer within an IP network must have an IP address that uniquely identifies that individual host. An Internet Protocol-based network (an IP Network)
is a group of hosts that share a
common physical connection and that use Internet Protocol for network layer communication.
The IP addresses in an IP network are contiguous,
that is, one address follows right after the other with no gaps.

Address Types in an IP Network

Within a given range of IP addresses used in every IP network are special addresses reserved for

In addition, a IP network has a subnet mask. The subnet mask is a value stored one each computer that allows that computer to identify which IP addresses are within the network to which they are attached, and which IP addresses are on an outside network.

Host address

A host’s IP address is the address of a specific
host on an IP network. All hosts on a network must have a unique IP
address. This IP address is usually not
the first or the last IP address in the range
of network IP addresses as the first IP
address and last IP address in the range
of IP addresses are reserved for special functions.
The host addresses are all the addresses in the IP network range of IP
addresses except the first and last IP addresses.
Host IP addresses allow network hostst to establish
one-to-one direct communication. This one-to-one communication is referred
to as unicast communication.

All host IP addresses can be split into two
parts: a network part and a host part. The network
part of the IP addresses identifies the IP
Network the host is a member of. The host part uniquely identifies
an individual host.

Network Address

The network address is the first IP address
in the range of IP addresses. To be more precise,
the network address is the address in which all binary bits in the host
portion of the IP address are set to zero.
The purpose of the Network Address is to allow hosts that provide special
network services to communicate. In practice, the network address is rarely
used for communication.

Broadcast Address

The broadcast IP address is the last IP
address in the range of IP addresses. To
be more precise, the broadcast address is the IP
address in which all binary bits in the host portion of the IP
address are set to one. The broadcast address is reserved and allows a
single host to make an announcement to all hosts on the network. This is called
broadcast communication and the last address in a network is used
for broadcasting to all hosts because it is the address where the host portion
is all ones. This special address also sometimes called the all hosts
address. Some vendors allow you to set an address other than the last address
as the broadcast address.

Note that each network has its own network and broadcast addresses. Network
addresses do not necessarilly have a zero in the decimal representation of
the host portion of their address.

EXAMPLE 1

Let’s take the example of an IP network that has an address range of 192.168.1.0 – 192.168.1.255 with an address mask of 255.255.255.0, which would be 192.168.1/24 in CIDR block notation:

 
Network
Host
 

Network Address (decimal)
192
.
168
.
1
.
0
All

zeroes

in the host portion

Network Address (binary)
11000000
.
10011000
.
0000001
.
00000000

First host address (decimal)
192
.
168
.
1
.
1

00000001
00000010
00000011
…
11111100
11111101
11111110

First host address (binary)
11000000
.
10011000
.
00000001
.
00000001

…and all the addresses in between.

Last host address (decimal)
192
.
168
.
1
.
254

Last host address (binary)
11000000
.
10011000
.
00000001
.
11111110

Broadcast Address (decimal)
192
.
168
.
1
.
255
All

ones

in the host portion

Broadcast Address (binary)
11000000
.
10011000
.
00000001
.
11111111

HINT: If this table is giving
you trouble, you might need help with binary.

EXAMPLE 2

Example 1 showed a standard “Class C” style range of addresses where the entire
last octet of the IP address is used for one network. Some networks have fewer
hosts and conservation of IP addresses is important, so using a subnet mask
reduces the number of hosts in a range of IP addresses on an IP network.

In example 2, we borrow 2 bits
from what would normally be the host portion and use it as bits that indicate
the network portion. This makes a smaller network of just 64 addresses, of
which 62 are usable for hosts. Remember, the first address in a range of IP
addresses is reserved for the network address. The last address in the IP address range
for the network is reserved for the broadcast address.

CAUTION:The CCNA exam will try to trip you up by asking how many
addresses are usable for hosts, which is always 2 less than the number
of addresses in the range of addresses in the subnet. Read your subnetting
questions carefully on the CCNA exam and understand whether they are talking about
the range of addresses, the number of host addresses, the number of networks,
the network address or the broadcast address.

192.168.1.0 / 255.255.255.192 (192.168.1/26)

 
network
portion
host
portion
 

Network Address (decimal)
192
.
168
.
1
.
64
First two bits reserved for sub-network
use.
Six bits for host use
All zeroes in the host portion.

Network Address (binary)
11000000
.
10011000
.
0000001
.
01000000

First host address (decimal)
192
.
168
.
1
.
65
01000001
01000010
…
01111101
01111110

First host address (binary)
11000000
.
10011000
.
00000001
.
01000001

…and all the addresses in between.

Last host address (decimal)
192
.
168
.
1
.
126

Last host address (binary)
11000000
.
10011000
.
00000001
.
01111110

Broadcast Address (decimal)
192
.
168
.
1
.
127
First two bits reserved for sub-network
use.
Six bits for host use
All ones in the host portion

Broadcast Address (binary)
11000000
.
10011000
.
00000001
.
01111111

HINT: If this table is giving
you trouble, you might need help with binary.

HOW IT WORKS

Your computer uses a a mask in its
network connection that allows it to determine whether the computer
it wants to talk to over the local network is actaully on the local
network or on a network outside the local network. If it is a computer
that is local, it will use a local protocol
to find the other computer’s hardware
address. If the other computer
is not local (it is outside the local network), then it will send the data to
the local gateway (usually called the default
gateway). Your computer will try
to determine the hardware address of the local
default gateway and will use the hardware
address in the Ethernet header
(or FDDI header or Token Ring header etc.). The Ethernet
frame will contain a payload which will be filled with IP data. The IP address
of the remote computer will be in this
payload as part of the IP header. Since the IP
address in the IP datagram is the remote computer,
but the Ethernet frame is addressed
to the local default gateway, the default
gateway will accept the Ethernet
frame, read the IP data, verify the IP address
is indeed outside the local network and then forward the IP
datagram over whatever other network connections the computer
has that will allow it to reach all the other outside networks.

That’s how Internet Protocol makes routing work in
a network with a default gateway.

Fact and Fiction

Routers are NOT used for local communication
on the local IP network. They are bypassed completely and are not required.
Routers are used to forward data into
different networks and to restrict broadcasts on the local network from swamping
external networks with traffic that is important only to the local network.

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