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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 1
IP Addressing
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IP Addressing
An IP address is a numeric identifier assigned to
each machine on an IP network.
Software address, 32-bit long divided into four
sections, referred to as octets.
4.3 billion address space
written in a format known as dotted decimal.
172.16.30.56
The 32-bit IP address is a structured or hierarchical
address.
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 2
IP Address Structure
IP addressing uses two-level (three-level) hierarchical addressing
structured by network and host, network, subnet and host.
The network address uniquely identifies each network segment
to which one or more hosts are connected.
Every machine on the same network shares that network address
as part of its IP address.
In the IP address 172.16.30.56, for example, 172.16 is the network
address.
The node address or host address is assigned to, and uniquely
identifies, each machine on a network.
This part of the address must be unique because it identifies a
particular machine—an individual— as opposed to a network,
which is a group.
In the sample IP address 172.16.30.56, the 30.56 is the node
address.
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IP Address Classes
The designers of the Internet decided to create classes of
networks based on network size.
For the small number of networks possessing a very large
number of hosts, they created the rank Class A network.
At the other extreme is the Class C network, which is reserved
for the numerous networks with a small number of hosts.
The class distinction for networks between very large and very
small is predictably called the Class B network.
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 3
Class of IP Address – Range
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 4
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 5
IPV4 Address
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Default subnet mask
A subnet mask is a 32-bit value that allows the recipient of IP
packets to distinguish the network ID portion of the IP address
from the host ID portion of the IP address.
The 1s in the subnet mask represent the positions that refer to
the network or subnet addresses.
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 6
Default subnet mask
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Special purpose / Reserved IPs
Some IP addresses are reserved for special purposes- can’t assigned to hosts.
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Link-local Addresses
In case a host is not able to acquire an IP address from the DHCP server and it has
not been assigned any IP address manually, the host can assign itself an IP address
from a range of reserved Link-local addresses. Link local address ranges from
169.254.0.0 — 169.254.255.255.
These IPs are also not routable.
Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 7
97
Link-local Addresses
In case a host is not able to acquire an IP address from the
DHCP server and it has not been assigned any IP address
manually, the host can assign itself an IP address from a range
of reserved Link-local addresses. Link local address ranges
from 169.254.0.0 — 169.254.255.255.
These IPs are also not routable.
Private IPs
These addresses can be used on a private network, but they’re not
routable through the Internet.
If every host on every network had to have real routable IP
addresses, we would have run out of IP addresses.
By using private IP addresses, ISPs, corporations, and home users
only need a relatively tiny group of IP addresses to connect their
networks to the Internet.
This is economical because they can use private IP addresses on their
inside networks.
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 8
Private IPs
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• These private addresses are used within an organization or site to allow devices to
communicate locally. However, because these addresses do not identify any single
company or organization over Internet, therefore, private IPv4 addresses cannot
be routed over the Internet.
Network Address Translation (NAT) is required to convert a private IP to real
(public) IP.
Network Address Translation
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Number of available IPv4 addresses is not enough.
Due to explosion of the Internet and the increase in home networks and
business networks.
The obvious solution is to redesign the address format to allow for more
possible addresses.
IPv6 – developed, but will take several years to implement because it
requires modification of the entire infrastructure of the Internet.
NAT (RFC 1631) comes to the rescue. Network Address Translation allows a
single device, such as a router, to act as an agent between the Internet (or
“public network”) and a local (or “private”) network.
Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 9
NAT
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NAT combined with private IPv4 addresses has
proven to be a useful method of preserving public
IPv4 addresses.
A single, public IPv4 address can be shared by
hundreds, even thousands, of devices, each
configured with a unique private IPv4 address.
Without NAT, the exhaustion of the IPv4 address
space would have occurred well before the year
2000.
NAT-Enabled Router
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NAT-enabled routers can be configured with one or more valid public IPv4 addresses.
These public addresses are known as the NAT pool. When an internal device sends traffic
out of the network, the NAT-enabled router translates the internal IPv4 address of the
device to a public address from the NAT pool.
Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 10
NAT address types
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Addresses used after NAT translations are called global addresses.
These are usually the public addresses used on the Internet
Local addresses are the ones we use before NAT translation.
So, the inside local address is actually the private address of the sending
host that’s trying to get to the Internet
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 11
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NAT working
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 12
Types of NAT
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Static NAT
Dynamic NAT
PAT (Port Address Translation)
Static NAT
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Static NAT uses a one-to-one mapping of local and global addresses. These
mappings are configured by the network administrator and remain
constant.
Basic static NAT configuration:
ip nat inside source static 10.1.1.1 170.46.2.2
Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 13
Dynamic NAT
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Dynamic NAT uses a pool of public addresses and assigns them on a first-
come, first-served basis. When an inside device requests access to an
outside network, dynamic NAT assigns an available public IPv4 address
from the pool.
Dynamic NAT configuration:
ip nat pool todd 170.168.2.2 170.168.2.254
netmask 255.255.255.0
ip nat inside source list 1 pool todd
PAT – NAT Overloading
With PAT, multiple
addresses can be mapped to
one or to a few addresses
because each private
address is also tracked by a
port number.
ip nat pool globalnet
170.168.2.1 170.168.2.1
netmask 255.255.255.0
ip nat inside source list 1
pool globalnet overload
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 14
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Network Address Translation
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 15
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 16
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Subject: Computer Networks 8/16/2024
Subject Teacher: Dr. Adnan Ahmed Arain, Dept.
of Cyber Security, QUEST, Nawabshah 17
Who governs the IP Address
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There are five Regional Internet Registries covering the whole world. They are:
•AFRINIC – African Network Information Centre
•APNIC -Asia-Pacific Network Information Centre
•ARIN – American Registry for Internet Numbers
•LACNIC – Latin America and Caribbean Network Information Centre
•RIP NCC – Réseaux IP Européens Network Coordination Centre
The RIRs are responsible for the allocation and management of IP addresses and AS
(Autonomous System) numbers to their respective local internet registries and the
internet service provider( ISP). The ISP further assigns the IP addresses to the end-users.
