Advanced Computer Networks: Lecture 18 - Dr. Amir Qayyum
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CS716
Advanced Computer Networks
By Dr. Amir Qayyum
1
Lecture No. 18
Internet Protocol (IP)
• Network protocol for the Internet
• Operates on all hosts and routers (routers connect
distinct networks into the Internet)
FTP
HTTP
NV
TFTP
UDP
TCP
IP
FDDI
Ethernet
…
ATM
3
Internetwork
• Concatenation of networks
H6
H7
H1
R1
Network
Network
11
Ethernet
Ethernet
Network 2
Point
to
point
H3
H2
R3
Network
Network
33
FDDI
FDDI
R2
Network
Network
44
Ethernet
Ethernet
H5
H8
H4
• Protocol stack
H1
H8
TCP
R1
IP
IP
ETH
R2
ETH
R3
IP
PPP
PPP
IP
FDDI
FDDI
TCP
IP
ETH
ETH
4
IP Addresses
7 bits (126 nets)
Class A:
0
24 bits (16 million hosts)
Network
Host
14 bits (16k nets)
Class B:
1
0
16 bits (64K hosts)
Network
21 bits (2 million nets)
Class C:
1
1
0
– 18.10.5.22
– 130.126.143.254
– 192.12.70.111
Network
Host
8 bits (256)
Host
host in class A network (MIT)
host in class B network (UIUC)
host in class C network
• More recent classes
– Multicast (class D): starts with 1110
– Future expansions (class E): starts with 1111
5
Datagram Format
0
4
Version
8
HLen
16
TOS
31
Length
Ident
TTL
19
Flags
Protocol
Offset
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable)
Data
•
•
•
•
•
4bit version (4 for IPv4, 6 for IPv6)
4bit header length (in words, minimum of 5)
8bit type of service (TOS); more or less unused
16bit datagram length (in bytes)
8bit protocol (e.g., TCP=6 or UDP=17)
6
Datagram Format
0
4
Version
8
HLen
16
TOS
31
Length
Ident
TTL
19
Flags
Protocol
Offset
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable)
Data
• Fragmentation support
– 16bit packet ID (identifies packet fragments)
– 3bit flags; one bit marks last fragment
– 13bit fragment offset into packet (in 8byte words)
• 8bit “timetolive” (TTL); a hop count until
forced destruction of packet
7
Datagram Format
•
•
•
•
16bit IP checksum on header
32bit source IP address
32bit destination IP address
Options and padding (variable length)
– Sourcebased routing (typically disabled)
0
4
8
16
– Record route
TOS
Version
HLen
– Several others
Ident
Flags
TTL
Protocol
19
31
Length
Offset
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable)
Data
8
