Transcript Internet Protocol

Internet Protocol
Internetworking Lab 1
Why Internet?
The Internet
Host 1
N1
N2
N3
N4
Host 2
Gateway
/Router
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 Bits in Max # of Bits in Max # of
Class Prefix Networks Suffix Hosts/net
A
7
128
24
16777216
B
14
16384
16
65536
C
21
2097152
8
256
Specific IP addresses
Prefix
Suffix Type of Addr
Purpose
All-0s
All-0s This computer
Used during
bootstrap
Identifies a network
Network All-0s Network
Network All-1s Directed broadcast Broadcast to a
All-1s
All-1s
127
Any
specific network
Limited broadcast Broadcast to local
net
Testing
Loopback
Network Mask
The network mask (subnet mask)
where there are 1’s indicates the network ID
where there are 0’s indicates the host ID
Examples
for a class A address: 255.0.0.0
for a class B address: 255.255.0.0
for a class C address: 255.255.255.0
IP functions
Fragmentation in IP
Host1
Host2
Network 3
MTU = 1400
Network 1
MTU = 1400
Router
Network 2
MTU = 600
Router
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
Fragmentation field
Original datagram
33
000
0
0, 1, 2, ………….1400
Fragmented datagram – fragment 1
33
001
0
0, 1, 2, ………….599
Fragmented datagram – fragment 2
33
001
75
600,601, ………….1199
Fragmented datagram – fragment 1
33
000
150
1200, 1201…….1400
IP properties
• Unreliable
• Connectionless - ?
• Best Effort