how ip address works
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TCP/IP Addressing DemystifiedTCP/IP Addressing Demystified - Edited by Alien Coders
Team
Contributed by Souvik
Official Website: http://www.aliencoders.com
Facebook Page: https://www.facebook.com/aliencoders
What you will learn
• How internet addressing works
• Internet Addressing
• Role played by Routing and addressing
• ARP
• TCP/UDP
• IPv6 into the picture
• The Internet Protocol (IP) enables communications across a vast and heterogeneous collection of networks.
• The Internet offers two basic communication services that operate on top of IP:
• TCP Transmission control protocol i.e reliable stream service.
• UDP User datagram Protocol.
The TCP header contains the port number of the client process and the well known port 80 for the HTTP server process.
The IP network address are the logical address because they are defined in terms of logical topology of the routers and the end systems.
Ethernet LAN frames contains physical address that identify the physical endpoints for the sender and the receiver.
• The network interface layer is particularly concerned with the protocols that are used to access the intermediate networks.
• At each gateway the network protocol is used to encapsulate the IP packet into a packet or frame of the underlying link.
• The router must determine the next hop in the route to the destination and then encapsulate the IP packet or frame of the type of the next network or link
IP Packet
• Total Length : With 16 bits , the max packet length = 65,535
• Protocol TCP =6 ; UDP =17 ; ICMP = 1
• Options : Security level , Route to be taken by the packet
• Padding : To make the header field a multiple of 32 bit word.
Network
Internet AddressingHost
An IP address is divided into 2 parts: a) network part 2) host part .
The part of a public IP address that identifies the network is internationally controlled by the Network Information Center (NIC) located in the Stanford Research Institute in California.
The part that identifies the host is controlled locally at a network level.
Internet Addressing
An Internet address is four octets (i.e. 32 bits) long.
The first few bits in the network part of the address helps interpret the address.These bits indicate the class of the address.
When a system wants to communicate over the internet they need to have a public address.
This public address has to be purchased from NIC in Stanford.
Address classes
There are five Internet address classes. They are : Class A / B / C / D / E .
Class A addressing is used for very large networks, that is networks which will have a large number of hosts attached to them.
For class A the MSB is 0.
Each pure class A network can support (224-2) hosts. One address each being reserved for network address (all 0 ) and all one for broad cast.
Class A
24 bits
Host ID
The first bit is 0 and next 7 bits called the Net ID identifies the network . The next field contains the host ID, which identifies the particular host within the specified network.
In a class A address it's 24 bits long and therefore allows for almost 17 million hosts on a network.
For example 10.200.20.5 is a class A address
Class B
Class B addressing is used for medium-sized networks.
If the first two bits in the address are 10, it's a class B address. 14 bits for network Ids and 16 bits for host Ids allowing about 16,000 networks and 64,000 hosts for each network.
The range of first octet of class B address is 128 –191.i.e 128.0.0.0 to 191.255.0.0
Class C
The next address class is class C, probably the most common network class. If the first 3 bits in the address are 110, the address is a class C address.
The net ID is 21 bits long and the host ID is 8 bits long, allowing about 21 million networks and 254 hosts per network.
The range of class C Network is 192.0.0.0 – 223.255.255.0
The 192.0.0.2555 is the broadcast address and 192.0.0.0 is the network address.
Class D
Class D addressing is used for multicasting a number of hosts for applications like audio and video conferencing.
Class D networks have the first 4 bits in the network part = 1110.
The first octet ranges from 224 – 239.
All the addressees from 224.0.0.0 to 239.255.255.255 can be used as multicast address.
All students in Internet Class!
• A host ID that contains all 1s is meant to broadcast the packet to all hosts specified by the network.
• If the network ID also contains all 1s the packet is broadcast on the local network.
• A host ID that contains all 0s refers to the network specified by the network ID , rather than to a host.
• A source may send all 0s in the source address while trying to find out the correct IP address. The machine is then identified by its MAC address.
• These are the IP address ranges reserved for private networks within organizations.
• These addresses will not be allocated by NIC as public IP address for the internet.
• There is no problem of clash because when a packet goes outside the organization the local IP address gets translated into into the public IP address purchased by the organizations.
Private Addressing
– Class A:• 10.0.0.0 to 10.255.255.255---- 1 Class A network
– Class B:• 172.16.0.0 to 172.31.255.255 ---- 16 contiguous Class B networks
– Class C:• 192.168.0.0 to 192.168.255.255--- 255 contiguous Class C networks
• These are IP address ranges reserved for private networks within organizations.
• These addresses will not be allocated by NIC as public IP addresses for the Internet.
• There is no problem of clash because when a packet goes outside the organization the local IP address gets translated into the public IP address purchased by the organization.
Reserved and Available IP Addresses
Reserved and Available IP Addresses
Class Address or Range Status
A 0.0.0.01.0.0.0 through 126.0.0.0127.0.0.0
ReservedAvailableReserved
B 128.0.0.0128.1.0.0 through 191.254.0.0191.255.0.0
ReservedAvailableReserved
C 192.0.0.0192.0.1.0 through 223.255.254223.255.255.0
ReservedAvailableReserved
D 224.0.0.0 through 239.255.255.255
Multicast group addresses
E 240.0.0.0 through 255.255.255.254255.255.255.255
ReservedBroadcast
• Subnet Addressing : To add another hierarchical level called the subnet .
• The beauty of the subnet addressing scheme is that it is oblivious to the network outside the organization.
• An organization has many LANs , each consisting of no more than 100 hosts.
• 7 bits for for host identification in a sub network and other 9 bits are used for identifying the subnetwork.
• Packet with destination IP 150.100. 12.176 arrives
• The subnet mask used is 11111111 11111111 11111111 10000000 = 255.255.255.128
• The router performs the AND between the subnet mask and the IP and the subnet number becomes 10010110 01100100 00001100 10000000 : 150.100.12.128
This number is used to forward the packet to the correct subnetwork.
IP Address Classes ExerciseIP Address Classes Exercise
Address Class Network Host
10.2.1.1
128.63.2.100
201.222.5.64
192.6.141.2
130.113.64.16
256.241.201.10
IP Address Classes Exercise Answers
IP Address Classes Exercise Answers
Address Class Network Host
10.2.1.1
128.63.2.100
201.222.5.64
192.6.141.2
130.113.64.16
256.241.201.10
A
B
C
C
B
Nonexistent
10.0.0.0
128.63.0.0
201.222.5.0
192.6.141.0
130.113.0.0
0.2.1.1
0.0.2.100
0.0.0.64
0.0.0.2
0.0.64.16
Subnet MaskSubnet Mask
172172 1616 00 00
255255 255255 00 00
255255 255255 255255 00
IPAddress
DefaultSubnet
Mask
8-bitSubnet
Mask
Network Host
Network Host
Network Subnet Host
Also written as “/16” where 16 represents the number of 1s in the mask.
Also written as “/24” where 24 represents the number of 1s in the mask.
11111111 11111111 00000000 00000000
Decimal Equivalents of Bit Decimal Equivalents of Bit PatternsPatterns
Decimal Equivalents of Bit Decimal Equivalents of Bit PatternsPatterns
1 0 0 0 0 0 0 0 = 128
1 1 0 0 0 0 0 0 = 192
1 1 1 0 0 0 0 0 = 224
1 1 1 1 0 0 0 0 = 240
1 1 1 1 1 0 0 0 = 248
1 1 1 1 1 1 0 0 = 252
1 1 1 1 1 1 1 0 = 254
1 1 1 1 1 1 1 1 = 255
128 64 32 16 8 4 2 1
16
Network Host
172 0 0
10101100
11111111
10101100
00010000
11111111
00010000
00000000
00000000
10100000
00000000
00000000
•Subnets not in use—the default
00000010
Subnet Mask without SubnetsSubnet Mask without Subnets
172.16.2.160172.16.2.160
255.255.0.0 255.255.0.0
NetworkNumber
•Network number is extended by eight bits
Subnet Mask with SubnetsSubnet Mask with Subnets
16
Network Host
172.16.2.160172.16.2.160
255.255.255.0 255.255.255.0
172 2 0
10101100
11111111
10101100
00010000
11111111
00010000
11111111
00000010
10100000
00000000
00000000
00000010
Subnet
Subnet Address
128
192
224
240
248
252
254
255
Subnet Mask with Subnets (cont.)
Subnet Mask with Subnets (cont.)Network Host
172.16.2.160172.16.2.160
255.255.255.192 255.255.255.192
10101100
11111111
10101100
00010000
11111111
00010000
11111111
00000010
10100000
11000000
10000000
00000010
Subnet
•Network number extended by ten bits
16172 2 128
SubnetAddress
128
192
224
240
248
252
254
255
128
192
224
240
248
252
254
255
Subnet Mask ExerciseSubnet Mask Exercise
Address Subnet Mask Class Subnet
172.16.2.10
10.6.24.20
10.30.36.12
255.255.255.0
255.255.240.0
255.255.255.0
Subnet Mask Exercise AnswersSubnet Mask Exercise Answers
Address Subnet Mask Class Subnet
172.16.2.10
10.6.24.20
10.30.36.12
255.255.255.0
255.255.240.0
255.255.255.0
B
A
A
172.16.2.0
10.6.16.0
10.30.36.0
Broadcast AddressesBroadcast Addresses
172.16.1.0
172.16.2.0
172.16.3.0
172.16.4.0
172.16.3.255(Directed broadcast)
255.255.255.255(Local network broadcast)
XX
172.16.255.255(All subnets broadcast)
Addressing Summary ExampleAddressing Summary Example16172 2 160
10101100 00010000 1010000000000010 Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
4
1
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
00000010 Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
00000010 Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
7
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
10000000
00000010 Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
4
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
10000000
00000010
10111111
Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
4
56
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
10000000
00000010
10111111
10000001
Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
4
56
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
00010000
11111111 11111111
10100000
11000000
10000000
00000010
10111111
10000001
10111110
Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
4
56
7
16172 2 160
Addressing Summary ExampleAddressing Summary Example
10101100
11111111
10101100
00010000
11111111
00010000
11111111
00000010
10100000
11000000
10000000
00000010
10101100 00010000 00000010 10111111
10101100 00010000 00000010 10000001
10101100 00010000 00000010 10111110
Host
Mask
Subnet
Broadcast
Last
First
172.16.2.160
255.255.255.192
1
2
3
4
56
7
8
16172 2 160
Routing Demonstration
ARP
192.168.89.20
192.168.89.40
192.168.88.20
192.168.88.40
192.168.89.2
192.168.88.2
192.168.90.2
192.168.90.3
192.168.91.3
192.168.91.4
Router BRouter C
Router A
Layer 2
Layer 2
Routing done by HostNetwork Destination
Netmask Gateway Interface
0.0.0.0 0.0.0.0 192.168.88.2 192.168.88.40
192.168.88.0 255.255.255.0 192.168.88.40
192.168.88.40
192.168.88.40 255.255.255.255
127.0.0.1 127.0.0.1
Let assume IP packet received by network layer of
host have destination IP 192.168.88.20 and source IP: 192.168.88.40
192.168.88.20
AND
255.255.255.255
192.168.88.20
192.168.88.20
AND
255.255.255.0
192.168.88.0
Routing done by HostNetwork Destination
Netmask Gateway Interface
0.0.0.0 0.0.0.0 192.168.88.2 192.168.88.40
192.168.88.0 255.255.255.0 192.168.88.40
192.168.88.40
192.168.88.40 255.255.255.255
127.0.0.1 127.0.0.1
Let assume IP packet received by network layer of
host have destination IP 192.168.89.4 and source IP: 192.168.88.40
192.168.89.4
AND
255.255.255.255
192.168.89.4
192.168.89.4
AND
255.255.255.0
192.168.89.0
192.168.89.4
AND
0.0.0.0
0.0.0.0
Network Destination
Netmask Gateway Interface
0.0.0.0 0.0.0.0 192.168.90.3 192.168.90.2
192.168.88.0 255.255.255.0
192.168.88.2 192.168.88.2
192.168.89.0 255.255.255.0
192.168.89.2 192.168.89.2
192.168.90.0 255.255.255.0
192.168.90.2 192.168.90.2
192.168.91.0 255.255.255.0
192.168.90.3 192.168.90.2
Let assume IP packet received by layer 3
have destination IP 192.168.89.4 and source IP: 192.168.88.40
192.168.89.4
AND
255.255.255.0
192.168.89.0
Routing Done Router A
Network Destination
Netmask Gateway Interface
0.0.0.0 0.0.0.0 192.168.91.4 192.168.91.3
192.168.88.0 255.255.255.0 192.168.90.2 192.168.90.3
192.168.89.0 255.255.255.0 192.168.90.2 192.168.90.3
192.168.90.0 255.255.255.0 192.168.90.3 192.168.90.3
192.168.91.0 255.255.255.0 192.168.91.3 192.168.91.3
Routing Done by Router B
Let assume IP packet received by Router A
have destination IP 192.168.92.5 and source IP: 192.168.88.40
192.168.92.5
AND
255.255.255.0
192.168.92.0
192.168.92.5
AND
0.0.0.0
0.0.0.0
Dynamic Routing
Routing Protocol
Interior Gateway Protocol Exterior Gateway Protocol
Open Shortest Path First Routing Information Protocol
Border Gateway Protocol
Dijkstra Algorithm Bellman Ford Algorithm
Link State Protocol Distance Vector Protocol
Address Resolution Protocol• The address resolution protocol (ARP) is used when
one host wants to get the physical address of
another host on the same network.
Address Resolution Protocol
Ignored
Ignored
Address Resolution Protocol
Address Resolution
Fragmentation and Reassembly
IPv6
USER DATAGRAM PROTOCOL
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