TCP/IP Protocols and ARP Address Mapping

MSIT541
Chapter 3 – Part II
TCP/IP Suite and Internet Stack
Protocols
3.II.1

MSIT541
The TCP/IP Protocol Suite
- Internet Protocol Version4 (IPv4)
 Protocols to be discussed in section:
NETWORK LAYER PROTOCOLS:
 ARP
 IPv4
3.II.2

MSIT541
Address Resolution Protocol(ARP)
- Address Mapping
 ARP is the mapping of logical address to its
corresponding physical address and vice versa.
 Anytime a host or a router has an IP datagram
to send to another host or router, it has the
logical (IP) address of the receiver.
 The IP datagram must be encapsulated in a
frame to be able to pass through the physical
network.
 This means that the sender needs the physical
address of the receiver.
3.II.3

MSIT541
- Address Mapping
 ARP accepts a logical address from the IP
protocol, maps the address to the
corresponding physical address and pass it to
the data link layer.
 Address mapping can be done using:
 static mapping or
 dynamic mapping.
3.II.4

MSIT541
- Address Mapping
static mapping
 Creates a table that associates a logical address
with a physical address
 The table is stored in each machine on the
network
 Some limitations because physical addresses
may change.
 To implement these changes, a static mapping
table must be updated periodically.
 This overhead could affect network performance.
3.II.5

MSIT541
- Address Mapping
static mapping
 Physical addresses may change in the following
ways:
 A machine could change its NIC, resulting in a new
physical address.
 In some LANs, such as LocalTalk, the physical
address changes every time the computer is turned
on.
 A mobile computer can move from one physical
network to another, resulting in a change in its
physical address.
3.II.6

MSIT541
- Address Mapping
dynamic mapping
 Each time a machine knows the logical address of
another machine, it can use a protocol to ﬁnd the
physical address
 Two protocols have been designed to perform
dynamic mapping:
 Address Resolution Protocol (ARP) - maps a logical
address to a physical address
 Reverse Address Resolution Protocol (RARP) - maps
a physical address to a logical address
3.II.7

MSIT541
- The ARP Protocol
 Position of ARP in TCP/IP protocol suite
3.II.8

MSIT541
- The ARP Protocol
3.II.9
broadcast
ARP operation
An ARP
request is
broadcast;
an ARP
reply is
unicast.

MSIT541
- The ARP Protocol
3.II.10
ARP packet

MSIT541
- The ARP Protocol
3.II.11
ARP packet

MSIT541
- The ARP Protocol
3.II.12
ARP packet

MSIT541
- The ARP Protocol
3.II.13
Encapsulation of ARP packet
Data
Preamble
and SFD
Destination
address
Source
address
Type CRC
8 bytes 6 bytes 6 bytes 2 bytes 4 bytes
Type: 0x0806
An ARP packet is encapsulated directly into a data link frame.

MSIT541
- The ARP Protocol
3.II.14
Four cases using ARP

MSIT541
- The ARP Protocol
3.II.15
Example - 1
A host with IP address 130.23.43.20 and
physical address B2:34:55:10:22:10 has a
packet to send to another host with IP
address 130.23.43.25 and physical
address A4:6E:F4:59:83:AB. The two
hosts are on the same Ethernet network.
Show the ARP request and reply packets
encapsulated in Ethernet frames.

MSIT541
- The ARP Protocol
3.II.16
The ARP data field in this case is 28 bytes, and that the
individual addresses do not fit in the 4-byte boundary. That is
why we do not show the regular 4-byte boundaries for these
addresses. Also note that the IP addresses are shown in
hexadecimal.

MSIT541
- The ARP Protocol
 Proxy ARP is used to create a subnetting effect
 It is an ARP that acts on behalf of a set of hosts.
 Whenever a router running a proxy ARP receives
an ARP request looking for the IP address of one
of these hosts, the router sends an ARP reply
announcing its own hardware (physical) address.
 After the router receives the actual IP packet, it
sends the packet to the appropriate host or
router.
3.II.17
Proxy ARP

MSIT541
- The ARP Protocol
3.II.18
Proxy ARP
Request

MSIT541
- ATM ARP
3.II.19
ATM ARP
• When IP packets are moving through an
ATMWAN, a mechanism protocol is needed to find
(map) the physical address of the exiting-point
router in the ATM WAN given the IP address of the
router.
• This is the same task performed by ARP on a LAN.
• However, there is a difference between a LAN and
an ATM network.
• A LAN is a broadcast network (at the data link
layer); ARP uses the broadcasting capability of
a LAN to send (broadcast) an ARP request.

MSIT541
- ATM ARP
3.II.20
ATMARP packet

MSIT541
- ATM ARP
3.II.21
ATMARP packet

MSIT541
- ATM ARP
3.II.22
ATMARP packet

MSIT541
- ATM ARP
3.II.23
ATMARP packet

MSIT541
- ATM ARP
3.II.24
ATMARP Operation
The inverse request and inverse reply messages can
bind the physical address to an IP address in a PVC
situation.

MSIT541
- ATM ARP
 There are two methods to connect two routers
on an ATM network:
 through a permanent virtual circuit (PVC) or
 through a switched virtual circuit (SVC).
3.II.25
ATMARP Operation

MSIT541
- ATM ARP
3.II.26
ATMARP Operation - PVC Connection
time time
Two routers connected through PVC
I II III
ATM
Inverse Request
1
Inverse Reply
2

MSIT541
Entering-point
router
Exiting-point
router
ATMARP
Server
Time Time
I III
II
ATM
- ATM ARP
3.II.27
ATMARP Operation
- SVC Connection
Using PVC or SVC
connection
Request
1
Reply
2
or
NACK
2
Finding physical
address

MSIT541
- ATM ARP
3.II.28
ATMARP Operation
• The request and reply message can be
used to bind a physical address to an IP
address in an SVC situation.
• The inverse request and inverse reply
can also be used to build the server’s
mapping table.

MSIT541
- ATM ARP
3.II.29
ATMARP Operation Building a table
A newly connected
router
Time Time
I II III
ATMARP
server
ATM
Inverse request
1
Inverse reply
2

MSIT541
- ATM ARP
 LIS allows an ATM network to be divided into
several logical subnets.
 To use ATMARP, we need a separate server for
each subnet.
 A router can communicate and send IP packets
directly to a router in the same subnet;
however, if it needs to send a packet to a router
that belongs to another subnet, the packet
must ﬁrst go to a router that belongs to both
subnets.
3.II.30
Logical IP Subnet (LIS)

MSIT541
- ATM ARP
3.II.31
Logical IP Subnet (LIS)

MSIT541
- ARP Package
 A simplified ARP software package involves
five components:
 a cache table,
 queues,
 an output module,
 an input module, and
 a cache-control module.
3.II.32

MSIT541
- ARP Package
3.II.33
ARP components

MSIT541
- ARP Package
3.II.34

MSIT541
- ARP Package
3.II.35

MSIT541
- ARP Package
3.II.36

MSIT541
- ARP Package
3.II.37

MSIT541
- ARP Package
3.II.38

MSIT541
- ARP Package
3.II.39
The ARP output module receives an IP datagram (from the IP
layer) with the destination address 114.5.7.89. It checks the
cache table and finds that an entry exists for this destination
with the RESOLVED state (R in the table). It extracts the
hardware address, which is 457342ACAE32, and sends the
packet and the address to the data link layer for transmission.
The cache table remains the same.
Example - 2

MSIT541
- ARP Package
3.II.40
Twenty seconds later, the ARP output module receives an IP
datagram (from the IP layer) with the destination address
116.1.7.22. It checks the cache table and does not find this
destination in the table. The module adds an entry to the table
with the state PENDING and the Attempt value 1. It creates a
new queue for this destination and enqueues the packet. It then
sends an ARP request to the data link layer for this destination.
The new cache table is shown in Table 8.6.
Example - 3

MSIT541
- ARP Package
3.II.41
Example - 3

MSIT541
- ARP Package
3.II.42
Example - 4
Fifteen seconds later, the ARP input module receives an ARP
packet with target protocol (IP) address 188.11.8.71. The
module checks the table and finds this address. It changes the
state of the entry to RESOLVED and sets the time-out value to
900. The module then adds the target hardware address
(E34573242ACA) to the entry. Now it accesses queue 18 and
sends all the packets in this queue, one by one, to the data link
layer. The new cache table is shown in Table 8.7.

MSIT541
- ARP Package
3.II.43
Example - 4

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- ARP Package
3.II.44
Example - 5
Twenty-five seconds later, the cache-control module updates
every entry. The time-out values for the first three resolved
entries are decremented by 60. The time-out value for the last
resolved entry is decremented by 25. The state of the next-to-
the last entry is changed to FREE because the time-out is zero.
For each of the three pending entries, the value of the attempts
field is incremented by one. After incrementing, the attempts
value for one entry (the one with IP address 201.11.56.7) is
more than the maximum; the state is changed to FREE, the
queue is deleted, and an ICMP message is sent to the original
destination. See Table 8.8.

MSIT541
- ARP Package
3.II.45
Example - 5

MSIT541
Internet Protocol Version4 (IPv4)
 In this section :
 Datagrams
 Fragmentation
 Options
 Checksum
 IP over ATM
 IP Package
3.II.46

MSIT541
 The Internet Protocol (IP) is the transmission
mechanism used by the TCP/IP protocols at the
network layer.
3.II.47
Position of IP in TCP/IP protocol suite

MSIT541
IPv4 - Datagrams
 Packets in the network (internet) layer are called
datagrams.
 A datagram is a variable-length packet consisting of
two parts: header and data.
 The header is 20 to 60 bytes in length and contains
information essential to routing and delivery.
 It is customary in TCP/IP to show the header in
4-byte sections.
3.II.48

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Datagram
packet format
IPv4 - Datagrams
3.II.49

MSIT541
IPv4 - Datagrams
3.II.50
Service type
Precedence
interpretation
0 0 0
x
x
x 0
0
1
x
x
x
x
x
x
x
x
x
x
x
x
1
1
Differential service
interpretation
x
Precedence deﬁnes the eight-level priority
of the datagram (0 to 7) in issues such as
congestion. Some datagrams in the Internet
are more important than the others.
If a router is congested and needs to
discard some datagrams, those datagrams
with lowest precedence are discarded ﬁrst.

MSIT541
IPv4 - Datagrams
3.II.51
Service type
Precedence
interpretation
0 0 0
x
x
x 0
0
1
x
x
x
x
x
x
x
x
x
x
x
x
1
1
Differential service
interpretation
x
 24 categories
 16 categories
16 categories

MSIT541
Datagram
packet format
IPv4 - Datagrams
3.II.52
The total length field defines
the total length of the datagram
including the header.
(Max datagram size is 216-1
bits. i.e 65535 Bytes 64KB)

MSIT541
If the size of an IP datagram is less than 46
bytes, some padding will be added to make it 46
bytes.
IPv4 - Datagrams
3.II.53
Encapsulation of a small datagram in an
Ethernet frame

MSIT541
IPv4 - Datagrams
3.II.54
Multiplexing
- An IP datagram can encapsulate data from several higher
level protocols such as TCP, UDP, ICMP, and IGMP.
- The protocol field of the header specifies the final
destination protocol to which the IP datagram should be
delivered.

MSIT541
IPv4 - Datagrams
3.II.55
Protocols

MSIT541
IPv4 - Datagrams
3.II.56
Examples
An IP packet has arrived with the first 8 bits as shown:
The receiver discards the packet. Why?
Solution
There is an error in this packet. The 4 left-most bits (0100)
show the version, which is correct. The next 4 bits (0010)
show the wrong header length (2 × 4 = 8). The minimum
number of bytes in the header must be 20. The packet has
been corrupted in transmission.

MSIT541
IPv4 - Datagrams
3.II.57
Examples
In an IP packet, the value of HLEN is 1000 in binary. How many
bytes of options are being carried by this packet?
Solution
The HLEN value is 8, which means the total number of bytes in
the header is 8 × 4 or 32 bytes. The first 20 bytes are the base
header, the next 12 bytes are the options.

MSIT541
IPv4 - Datagrams
3.II.58
Examples
In an IP packet, the value of HLEN is 516 and the value of the
total length field is 002816. How many bytes of data are being
carried by this packet?
Solution
The HLEN value is 5, which means the total number of bytes in
the header is 5 × 4 or 20 bytes (no options). The total length is
40 bytes, which means the packet is carrying 20 bytes of data
(40 − 20).

MSIT541
IPv4 - Datagrams
3.II.59
Examples
An IP packet has arrived with the first few hexadecimal digits as
shown below:
How many hops can this packet travel before being dropped?
The data belong to what upper layer protocol?
Solution
To find the time-to-live field, we skip 8 bytes (16 hexadecimal
digits). The time-to-live field is the ninth byte, which is 01. This
means the packet can travel only one hop. The protocol field is
the next byte (02), which means that the upper layer protocol is
IGMP (see Table 7.2)

MSIT541
IPv4 - FRAGMENTATION
3.II.60
 A datagram can travel through different networks.
 Each router decapsulates the IP datagram from the
frame it receives, processes it, and then
encapsulates it in another frame.
 The format and size of the received frame depend
on the protocol used by the physical network
through which the frame has just traveled.
 The format and size of the sent frame depend on
the protocol used by the physical network through
which the frame is going to travel.

MSIT541
3.II.61
Maximum Transfer Unit (MTU)
N.B :- Only data in a datagram is fragmented.

MSIT541
3.II.62
Fields Related to Fragmentation

MSIT541
3.II.63
Fields Related to Fragmentation
Identification - This 16-bit field identifies a
datagram originating from the source host.
Flags - This is a three-bit field. The first bit is
reserved (not used). The second bit is called the do
not fragment bit. The third bit is called the more
fragment bit.
Fragmentation offset - This 13-bit field shows the
relative position of this fragment with respect to the
whole datagram.

MSIT541
3.II.64
Example
0000 1399
Offset = 0000/8 = 0
1400 2799
Offset = 1400/8 = 175
2800 3999
Offset = 2800/8 = 350
Notice that the value of the offset is measured in units
of 8 bytes. This is because the length of the offset ﬁeld
is only 13 bits long and cannot represent a sequence of
bytes greater than 8191. This forces hosts or routers
that fragment datagrams to choose the size of each
fragment so that the ﬁrst byte number is divisible by 8.

MSIT541
3.II.65
Example
000
4020
14,567
Bytes 0000–3999
Original datagram
0
175
1420
14,567
Bytes 1400–2799
Fragment 2
1
350
1220
14,567
Bytes 2800–3999
Fragment 3
0
175
820
14,567
Bytes 1400–2199
Fragment 2.1
1
Fragment 1
000
1420
14,567
Bytes 0000–1399
1

MSIT541
A packet has arrived with an M bit value of 0. Is
this the first fragment, the last fragment, or a
middle fragment? Do we know if the packet was
fragmented?
Solution
If the M bit is 0, it means that there are no more
fragments; the fragment is the last one. However,
we cannot say if the original packet was
fragmented or not. A nonfragmented packet is
considered the last fragment.
Example
3.II.66

MSIT541
A packet has arrived with an M bit value of 1. Is this the first
fragment, the last fragment, or a middle fragment? Do we
know if the packet was fragmented?
Solution
If the M bit is 1, it means that there is at least one more
fragment. This fragment can be the first one or a middle
one, but not the last one. We don’t know if it is the first one
or a middle one; we need more information (the value of the
fragmentation offset). See also the next example.
Example
3.II.67

MSIT541
A packet has arrived with an M bit value of 1 and a
fragmentation offset value of zero. Is this the first fragment,
the last fragment, or a middle fragment?
Solution
Because the M bit is 1, it is either the first fragment or a
middle one. Because the offset value is 0, it is the first
fragment.
Example
3.II.68

MSIT541
A packet has arrived in which the offset value is 100. What
is the number of the first byte? Do we know the number of
the last byte?
Solution
To find the number of the first byte, we multiply the offset
value by 8. This means that the first byte number is 800. We
cannot determine the number of the last byte unless we
know the length of the data.
Example
3.II.69

MSIT541
A packet has arrived in which the offset value is 100, the
value of HLEN is 5 and the value of the total length field is
100. What is the number of the first byte and the last byte?
Solution
The first byte number is 100 × 8 = 800. The total length is
100 bytes and the header length is 20 bytes (5 × 4), which
means that there are 80 bytes in this datagram. If the first
byte number is 800, the last byte number must be 879.
Example
3.II.70

MSIT541
3.II.71
 The header of the IP datagram is made of two
parts:
 a fixed part and
 a variable part.
 The fixed part is 20 bytes long and was discussed
in the previous section.
 The variable part comprises the options, which can
be a maximum of 40 bytes.
IPv4 - OPTIONS

MSIT541
3.II.72
 Options, as the name implies, are not required for a
datagram.
 They can be used for network testing and
debugging.
 Although options are not a required part of the IP
header, option processing is required of the IP
software.
IPv4 - OPTIONS

MSIT541
3.II.73
 Option format
IPv4 - OPTIONS
Type Length
8 bits 8 bits
Value
Variable length
Copy
0 Copy only in first fragment
1 Copy into all fragments
Class
00 Datagram control
01 Reserved
10 Debugging and management
11 Reserved
Number
00000 End of option
00001 No operation
00011 Loose source route
00100 Timestamp
00111 Record route
01001 Strict source route

MSIT541
3.II.74
Categories of options
IPv4 - OPTIONS

MSIT541
3.II.75
Option Types - No operation option
IPv4 - OPTIONS
A no-operation option is a 1-byte option used
as a ﬁller between options.

MSIT541
3.II.76
Option Types - Endo-of-option option
IPv4 - OPTIONS
An end-of-option option is also a 1-byte
option used for padding at the end of the
option ﬁeld. It, however, can only be used as
the last option.

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3.II.77
Option Types - Record-route option
IPv4 - OPTIONS
A record-route option is used to record the
Internet routers that handle the datagram.

MSIT541
3.II.78
Option Types - Record-route concept
IPv4 - OPTIONS
67.34.30.6 138.6.25.40
67.14.10.22
140.10.0.0/16
140.10.5.4
200.14.7.9 200.14.7.0/24
200.14.7.14
138.6.22.26
138.6.0.0/16
140.10.6.3
Network Network Network Network
67.0.0.0/24
7 15 7 15
140.10.6.3
7 15 12
140.10.6.3
200.14.7.9
7 16
15
140.10.6.3
200.14.7.9
138.6.22.26
4 8

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3.II.79
Option Types - Strict-source-route option
IPv4 - OPTIONS
A strict-source-route option is used by the
source to predetermine a route for the
datagram as it travels through the Internet.

MSIT541
3.II.80
Option Types - Strict-source-route option
IPv4 - OPTIONS
67.34.30.6 138.6.25.40
67.14.10.22
140.10.0.0/16
140.10.5.4
200.14.7.9 200.14.7.0/24
200.14.7.14
138.6.22.26
138.6.0.0/16
140.10.6.3
67.0.0.0/24
Source: 67.34.30.6
Destination: 67.14.10.22
200.14.7.14
140.10.5.4
4
15
137
138.6.25.40
Destination:140.10.5.4
Source: 67.34.30.6
8
15
137
138.6.25.40
67.14.10.22
200.14.7.14
Source: 67.34.30.6
12
15
137
138.6.25.40
67.14.10.22
140.10.5.4
Source: 67.34.30.6
16
15
137
67.14.10.22
200.14.7.14
140.10.5.4

MSIT541
3.II.81
Option Types - Loose-source-route option
IPv4 - OPTIONS
A loose-source-route option is similar to the
strict source route, but it is more relaxed.
Each router in the list must be visited, but the
datagram can visit other routers as well.

MSIT541
3.II.82
Option Types - Time-stamp option
IPv4 - OPTIONS
- A timestamp option is used to record the
time of datagram processing by a router.
- The time is expressed in milliseconds from
midnight, Universal Time.
- Knowing the time a datagram is processed
can help users and managers track the
behavior of the routers in the Internet.
- We can estimate the time it takes for a
datagram to go from one router to another.

MSIT541
3.II.83
Option Types - Time-stamp option
IPv4 - OPTIONS

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3.II.84
Use of flags in timestamp
IPv4 - OPTIONS

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3.II.85
Timestamp concept
IPv4 - OPTIONS
67.34.30.6
67.14.10.22
140.10.0.0/16
140.10.5.4
200.14.7.9
200.14.7.0/24
200.14.7.14
138.6.22.26
138.6.0.0/16
140.10.6.3
67.0.0.0/24
68 28 0
5 1 68 28 13 0 1
140.10.6.3
36000000
68 28 21 0 1
140.10.6.3
36000000
200.14.7.9
36000012
68 28 29 0 1
140.10.6.3
36000000
200.14.7.9
138.6.22.26
36000012
36000020

MSIT541
Which of the six options must be copied to each fragment?
Solution
We look at the first (left-most) bit of the type for each option.
a. No operation: type is 1 (i.e - 00000001); not copied.
b. End of option: type is 0 (i.e – 00000000); not copied.
c. Record route: type is 7 (i.e – 00000111); not copied.
d. Strict source route: type is 137 (i.e – 10001001); copied.
e. Loose source route: type is 131 (i.e – 10000011); copied.
f. Timestamp: type is 68 (i.e – 01000100); not copied.
3.II.86
IPv4 - OPTIONS
Examples

MSIT541
Which of the six options are used for datagram control and
which for debugging and managements?
Solution
We look at the second and third (left-most) bits of the type.
a. No operation: type is 00000001; datagram control.
b. End of option: type is 00000000; datagram control.
c. Record route: type is 00000111; datagram control.
d. Strict source route: type is 10001001; datagram control.
e. Loose source route: type is 10000011; datagram control.
f. Timestamp: type is 01000100; debugging and
management control.
3.II.87
IPv4 - OPTIONS
Examples

MSIT541
3.II.88
IPv4 - OPTIONS
Examples
- Run the following command from the windows
command prompt application
tracert www.ethiotelecom.et
- Inspect the various options of the above
command and investigate the result.
The Traceroute command (Tracert on Windows) is a
small network diagnostic software that you have built-in
on your device and servers for tracing the route, hop by
hop to a target.

MSIT541
One of the utilities available in UNIX to check the traveling of
the IP packets is ping. In the next chapter, we talk about the
ping program in more detail. In this example, we want to
show how to use the program to see if a host is available. We
ping a server at De Anza College named fhda.edu. The result
shows that the IP address of the host is 153.18.8.1. The
result also shows the number of bytes used.
3.II.89
IPv4 - OPTIONS
Examples

MSIT541
We can also use the ping utility with the -R option to
implement the record route option. The result shows the
interfaces and IP addresses.
3.II.90
IPv4 - OPTIONS
Examples

MSIT541
The traceroute utility can also be used to keep track of the
route of a packet. The result shows the three routers visited.
3.II.91
IPv4 - OPTIONS
Examples

MSIT541
The traceroute program can be used to implement loose
source routing. The -g option allows us to define the routers
to be visited, from the source to destination. The following
shows how we can send a packet to the fhda.edu server with
the requirement that the packet visit the router 153.18.251.4.
3.II.92
IPv4 - OPTIONS
Examples

MSIT541
The traceroute program can also be used to implement strict
source routing. The -G option forces the packet to visit the
routers defined in the command line. The following shows
how we can send a packet to the fhda.edu server and force
the packet to visit only the router 153.18.251.4.
3.II.93
IPv4 - OPTIONS
Examples

MSIT541
3.II.94
IPv4 - CHECKSUM
 The error detection method used by most TCP/IP
protocols is called the checksum.
 The checksum protects against the corruption that
may occur during the transmission of a packet.
 It is redundant information added to the packet.
 The checksum is calculated at the sender and the
value obtained is sent with the packet.
 The receiver repeats the same calculation on the
whole packet including the checksum.
 If the result is satisfactory (see below), the packet is
accepted; otherwise, it is rejected.

MSIT541
3.II.95
IPv4 - CHECKSUM
 Checksum concept
Checksum
Packet
n bits
n bits
n bits
n bits
n bits
n bits
n bits
Section 1
Sum
Complement
Result
Section 2
Checksum
Section k
Receiver
..............
..............
If the result is 0, keep;
otherwise, discard.

MSIT541
3.II.96
IPv4 - CHECKSUM
 Checksum in one’s complement arithmetic
Sender
Sum : T
Checksum : _T
Datagram
_T
T
Checksum in IP covers only the
header, not the data.

MSIT541
3.II.97
IPv4 - CHECKSUM
The figure on the following slide shows an
example of a checksum calculation at the
sender site for an IP header without options.
The header is divided into 16-bit sections. All
the sections are added and the sum is
complemented. The result is inserted in the
checksum field.
Examples

MSIT541
3.II.98
IPv4 - CHECKSUM
Examples
Example of checksum calculation at the sender

MSIT541
3.II.99
IPv4 - CHECKSUM
The figure on the following slide shows the checking of
checksum calculation at the receiver site (or intermediate
router) assuming that no errors occurred in the header. The
header is divided into 16-bit sections. All the sections are
added and the sum is complemented. Since the result is 16 0s,
the packet is accepted.
Examples

MSIT541
3.II.100
IPv4 - CHECKSUM
Examples
Example of checksum calculation at the receiver

MSIT541
3.II.101
IPv4 - IP OVER ATM
 In the previous sections, we assumed that the
underlying networks over which the IP datagrams
are moving are either LANs or point-to-point WANs.
 In this section, we want to see how an IP datagram
is moving through a switched WAN such as an
ATM.
 We will see that there are similarities as well as
differences.

MSIT541
3.II.102
IPv4 - IP OVER ATM
 The IP packet is encapsulated in cells (not just
one).
 An ATM network has its own definition for the
physical address of a device.
 Binding between an IP address and a physical
address is attained through a protocol called
ATMARP.

MSIT541
3.II.103
IPv4 - IP OVER ATM
An ATM WAN in the Internet
The AAL(ATM Adaptation Layer) layer used by
the IP protocol is AAL5.

MSIT541
3.II.104
IPv4 - IP OVER ATM
Entering-point and exiting-point routers
ATM Network
ATM cell
Entering-point
router
Exiting-point
router
I II III
IP Packet
IP
Packet

MSIT541
3.II.105
IPv4 - IP OVER ATM
Address binding in IP over ATM

MSIT541
3.II.106
IPv4 - IP PACKAGE
 Header-Adding Module
 Processing Module
 Queues
 Routing Table
 Forwarding Module
 MTU Table
 Fragmentation Module
 Reassembly Table
 Reassembly Module
IP components

MSIT541
3.II.107
IPv4 - IP PACKAGE
Relationships
between the
different
concepts
discussed
so far
IP components

MSIT541
3.II.108
IPv4 - IP PACKAGE
IP components

MSIT541
3.II.109
IPv4 - IP PACKAGE
IP components

MSIT541
3.II.110
IPv4 - IP PACKAGE
IP components

MSIT541
3.II.111
IPv4 - IP PACKAGE
IP components

MSIT541
3.II.112
IPv4 - IP PACKAGE
IP components
Reassembly table

MSIT541
3.II.113
IPv4 - IP PACKAGE
IP components - Reassembly table
1. What does “value=0 & M=0” represent?
2.Why return here?
CHECK THE FRAGMENTATION
EXAMPLES FOR CLUES!!
How can the module determine if “all
fragments have arrived”?
CHECK THE FRAGMENTATION
EXAMPLES FOR CLUES!!

TCP/IP Protocols and ARP Address Mapping

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