Internet Protocol

Internetworking Lab 1

Why Internet?

The Internet

Host 1

Gateway /Router Host 2

N1

N4

N2

N3

Protocols for Inter-network

• TCP/IP protocol suite– TCP /UDP – layer 4 – Transport layer– IP network layer

• Forward packets from network to network

• Unique address which is globally recognized– Why not MAC/Physical addresses

• Routing ( algorithms, decisions, tables )

Internet Protocol - Goals

• Single seamless communication• Physical network details to be hidden from

applications– Hardware details– Software details

• Addressing mechanism to locate the network/machine (independent of MAC/Phy address)

Internet Protocol Goals

• Based on the location of the network – forward the packets

• For this purpose use – routing algorithms and tables

Solution – IP functions

• Provide an addressing mechanism– IP addresses

• IP layer ( network layer) to provide Routing and forwarding mechanisms

• Is not Reliable – No guarantees

• Best Effort Delivery

IP Address

• 32 bits or 4 bytes• Each byte – 255 decimal – FF (hex)• Typical address 129.21.21.3

– Dotted quad, dotted decimal

• Two parts – – Network id – locates the network – used in

routing– Host id – identifies the host in the network

Classes of IP address

• Class A– Network id is in 1st byte, host id in the rest 3

• Class B– Network id is in first two bytes, host id in the last 2

• Class C– Network id is in the first three bytes, host id in the last

byte

• Class D and E – special cases

Classes of IP addresses

Identifying class

CLASS Range of Values

A 0-127

B 128-191

C 192-223

D 224-239

E 240-255

Number of networks and hosts

Address Class

Bits in Prefix

Max # of Networks

Bits in Suffix

Max # of Hosts/net

A 7 128 24 16777216

B 14 16384 16 65536

C 21 2097152 8 256

Specific IP addressesPrefix Suffix Type of Addr Purpose

All-0s All-0s This computer Used during bootstrap

Network All-0s Network Identifies a network

Network All-1s Directed broadcast Broadcast to a specific network

All-1s All-1s Limited broadcast Broadcast to local net

127 Any Loopback Testing

Network Mask

The network mask (subnet mask)where there are 1’s indicates the network IDwhere there are 0’s indicates the host ID

Examplesfor a class A address: 255.0.0.0for a class B address:255.255.0.0for a class C address:255.255.255.0

IP functions

Fragmentation in IP

Network 1 MTU = 1400

Network 2 MTU = 600

Network 3 MTU = 1400

Router Router

Host1 Host2

Fragmentation in IP

• Identification– used to determine which fragments belong to each

other

• Flag– D flag =0– data may be fragmented

– =1 data may not be fragmented

• Fragment offset– indicates where a fragment belongs in the complete

message – measured in octets

Fragmentation field

ID 16bits

FLAGS 3bits

Offset 13 bits

33 000 0 0, 1, 2, ………….1400

33 001 0 0, 1, 2, ………….599

33 001 75 600,601, ………….1199

33 000 150 1200, 1201…….1400

Fragmentation field

Original datagram

Fragmented datagram – fragment 1

Fragmented datagram – fragment 2

Fragmented datagram – fragment 1

IP properties

• Unreliable

• Connectionless - ?

• Best Effort