Transcript Introduction to IP Part I Neil Tang 10/24/2008

Introduction to IP
Part I
Neil Tang
10/24/2008
CS440 Computer Networks
1
Overview
 Overview of IP
 Fragmentation
 IP Address
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Major Issues
 Heterogeneity
 Scalability
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Internet
Internet is a network of networks
Netw ork 1 (Ethernet)
H1
H2
H7
H3
R3
H8
Netw ork 4
(point-to-point)
Netw ork 2 (Ethernet)
R1
R2
H4
Netw ork 3 (FDDI)
H5
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H6
4
Internet Protocol
H1
H8
TCP
R1
IP
ETH
R2
IP
ETH
R3
IP
FDDI
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FDDI
IP
PPP
PPP
TCP
IP
ETH
ETH
5
IP Service Model
 Datagram Delivery Scheme: Best effort
 Addressing Scheme
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Datagram Delivery Scheme
 Best Effort
 Out-of-Order Delivery: IP will not attempt to resolve it. The
upper layer protocol (e.g., TCP) will handle that.
 Design Philosophy: Simple.
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IP Packet Format
0
4
Version
8
HLen
16
TOS
31
Length
Ident
TTL
19
Flags
Protocol
Offset
Checksum
SourceAddr
DestinationAddr
Options (variable)
Data
Pad
(variable)
Min header length = 5 words
= 20bytes=160bit
TTL: It is initialized to 64 and
will be deducted by one
every time the packet passes
a router.
Protocol: Specify the upper
layer protocols.
Address Field: 32bit
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Fragmentation and Reassembly
 Every kind of network has a Maximum Transmission Unit
(MTU), which is the largest IP datagram that it can carry in
a frame.
 Fragmentation typically occurs in a router when it receives
a datagram that it wants to forward over a network that
has an MTU smaller than the received datagram.
 The receiving host will reassemble the datagrams with the
same identifiers in the “ident” field.
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Fragmentation and Reassembly
H1
R1
R2
R3
R1
R2
R3
ETH IP (1400)
FDDI IP (1400)
H8
PPP IP (512)
ETH IP (512)
PPP IP (512)
ETH IP (512)
PPP IP (376)
ETH IP (376)
 Ethernet MTU = 1500 bytes
 FDDI MTU = 4500 bytes
 PPP MTU = 532 bytes
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Fragmentation and Reassembly
Start of header
Ident = x
0 Offset = 0
Rest of header
(a)
1400 data bytes
Start of header
Ident = x
1 Offset = 0
Rest of header
512 data bytes
(b)
Start of header
Ident = x
1 Offset = 64
Rest of header
512 data bytes
Start of header
Ident = x
0 Offset = 128
Rest of header
376 data bytes
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IP Address
 Hierarchical Address: An IP address consists of two parts,
network part and host part.
 A router (gateway) usually has multiple IP address, each
of which corresponds to a particular Network Interface
Card (NIC).
 IP addresses are usually divided to five classes.
 An IP address is usually represented as four decimal
integers separated by dots, e.g., 72.14.207.99
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IP Address Classes
7
(a)
0
24
Network
14
(b)
1
0
16
Network
Host
21
(c)
1
1
0
1/2 of addresses belong
to class A
Host
Network
1/4
8
Host
1/8
28
(d)
1
1
1
0
Host
1/16 Multicast
28
(e)
1
1
1
1
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Host
1/16 Experimental use
13