1. Advanced Computer Networks
CS716
Advanced Computer Networks
By Dr. Amir Qayyum 1

2. Lecture No. 18

3. 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
TCP
UDP IP …
FDDI
Ethernet
ATM

4. Internetwork Concatenation of networks Protocol stack Network 1H6 H7 H1 R3
Network 1
Ethernet
Network 3
FDDI
Network 4
Ethernet R1
Network 2
Point
-to-
point R2 H5 H8 H2 H3 H4 H1 H8
TCP R1 R2 R3
TCP IP IP IP IP IP
ETH
ETH
PPP
PPP
FDDI
FDDI
ETH
ETH

5. IP Addresses More recent classes
Network
Host
7 bits (126 nets)
24 bits (16 million hosts)
Class A:
14 bits (16k nets)
16 bits (64K hosts) 1
Class B:
21 bits (2 million nets)
8 bits (256)
Class C:
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

6. Datagram Format 4-bit version (4 for IPv4, 6 for IPv6)
HLen
TOS
Length
Ident
Flags
Offset
TTL
Protocol
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable) 4 8 16 19 31
Data
4-bit version (4 for IPv4, 6 for IPv6)
4-bit header length (in words, minimum of 5)
8-bit type of service (TOS); more or less unused
16-bit datagram length (in bytes)
8-bit protocol (e.g., TCP=6 or UDP=17)

7. Datagram Format Fragmentation supportV
ersion
HLen
TOS
Length
Ident
Flags
Offset
TTL
Protocol
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable) 4 8 16 19 31
Data
Fragmentation support
16-bit packet ID (identifies packet fragments)
3-bit flags; one bit marks last fragment
13-bit fragment offset into packet (in 8-byte words)
8-bit “time-to-live” (TTL); a hop count until forced destruction of packet

8. Datagram Format 16-bit IP checksum on header 32-bit source IP address
32-bit destination IP address
Options and padding (variable length)
Source-based routing (typically disabled)
Record route
Several others V
ersion
HLen
TOS
Length
Ident
Flags
Offset
TTL
Protocol
Checksum
SourceAddr
DestinationAddr
Options (variable)
Pad
(variable) 4 8 16 19 31
Data