The document discusses DHCP, NAT, and forwarding of IP packets. It begins by explaining DHCP and how DHCP servers dynamically assign IP addresses and network configuration parameters to devices on a network. It then covers network address translation, how NAT allows private IP addresses to be mapped to public IP addresses. The document concludes by discussing how routers forward IP packets based on the destination address, and methods for routing tables and longest prefix matching to determine the appropriate path for packet forwarding.

1. DCHP,NAT,FORWARDING
OF IP PACKETS
R.Pavithra -MSc(IT)
Department of CS& IT
Nadar saraswathi college of arts &
science

2. CONTENTS
Dynamic host configuration
protocol
Network address resolution
Forwarding of IP packets

3. DYNAMIC HOST CONFIGURATION
PROTOCOL
 The dynamic host
configuration protocol
is a network
management protocol
used on UDP/IP
networks whereby a
DHCP server
dynamically assigns an
IP address and other
network configuration
parameters to each
device on a network so
they can communicate
with other IP networks.

4. DHCP MESSAGE FORMAT:
DHCP Message format hops : Number of
Relay agents a request message traveled .xid :
Transaction ID, a random number chosen by
the client to identify an IP address allocation .
Secs : filed in by the client. The number of
seconds elapsed since the client began address
acquisition or renewal process.

6. DHCP OPERATION
 DHCP works in a
client/server mode and
operates like any other
client/server relationship .
when a PC connects
DHCP server. The server
assigns or lease an IP
address to that PC. Which
enables The PC ,connects
to the network with that
leased IP address until the
lease expire.

7. TWO WELL-KNOWN PORTS
 The DHCP employs a
connectionless service model,
using the user datagram
protocol(UDP) . It is implement
with two UDP port numbers for
its operations which are the
same as for the bootstrap
protocol (BOOTP). UDP port
number 67 is the destination
port of a server, and UDP port
number ^* is used by the client.

8. USING FTP
Software install-FTP/DHCP:
 A dhcpd.conf file on the FTP/DHCP server
tells the 2020 IMG where to go to retrieve the
system software and license file. Once
configured, the 2020 IMG boots from the
FTP/DHCP server and retrieves both the IP
address of software and the CTRL 0 interface
on the 2020 IMG and the location of the
system software and license files.

9. ERROR CONTROL
 IP address allocation
errors in DHCP:
 When a client attempts
obtain or verify an IP
address, you might see
problems logged to
syslog or in server
debugging mode
output. The following
list of common error
message indicates the
possible causes and
solutions.
 Cause:
A client is requesting a
specific IP address or seeking
to extend a lease on its current
IP address. The DHCP server
cannot find the DHCP network
table for that address
o Solution:
The DHCP network table
might have been deleted
mistakenly, you can recreate
the network table by adding
the network again using DHCP
manager or the dhcp configure
command.

10. TRANSITION STATES
 The DHCP has been
devised to provide static
and dynamic address
allocation. To provide
dynamic address
allocation, the DHCP
client acts as a state
machine that performs
transitions from one state
to another depending on
the messages it receives
or sends.

11. NETWORK ADDRESS RESOLUTION
 Network address
translation is a method of
remapping one IP address
space into another by
modifying network
address information in the
IP header of packets
while they are in transit
across a traffic routing
device.

12. ADDRESS TRANSLATION
 Network address translation (NAT) is a method
of remapping one IP address space into another
by modifying network address information in the
IP header of packets while they are in transit
across a traffic routing device. The technique
was originally used as a short cut to avoid the
need to readdress every host when a network
was moved. it has become and essential tool in
conserving global address space in the face of
IPV4 address exhaustion. One internet-routable
IP address of a NAT gateway can be used for an
entire private network.

14. TRANSLATION TABLE
 Translation table A table
of information stored
within a processor or
peripheral that is used to
convert encoded
information into another
form of encode with the
same meaning. A
translation table is used to
make the required
conversion.

15. USING IP ADDRESS
 Network address
translation (NAT)is a
process in which one or
more global Ip address
and vice versa in order to
provide internet access to
the local hosts.

16. USING POOL OF IP ADDRESS
 In the vision client, right-click the device and
choose inventory.
 In the inventory window, choose logical
inventory>context> IP Pools. A list of IP pools are
display in the content pane.
Field name Description
Table types Display the type of
table ,which is IP Pools.

17. USING BOTH IP ADDRESS AND PORT
ADDRESS
 The IP address is numerical label assigned to each device
connected to a computer network that uses the internet
protocol for communication. The port number is used to
direct the data to the correct location within this device .

18. FORWARDING IP PACKETS
 Packet forwarding is done when ulp receives a packet
that has a destination IP address that does not match any
of the IP addresses of the node. A node typically has
multiple addresses: one or more unicast address and at
least one broadcast or multicast address

19. FORWARDING BASED ON DESTINATION
 Forwarding based on
destination address and
label A connectionless
network(datagram
approach),a router
forwards a packet based
on the destination address
in the header of packet. A
connection-oriented
network(virtual-circuit
approach), a switch
forwards a packet based
on the label attached to
packet.

20. ADDRESS AGGREGATION
 It alleviates the
problem of increased
size of the table which
results in an increase
in the amount of time
needed to search the
table.

21. LONGEST MASK MATCHING
 Longest prefix
match(also called
maximum prefix
length match) refers
to an algorithm
used by routers in
internet protocol(
IP) networking to
select an entry from
a forwarding table.

22. HIERARCHICAL ROUTING
 Hierarchical routing is the
procedure of arranging
routers in a hierarchical
manner. A good example
would be to consider a
corporate internet. Most
corporate intranets consist
of a high speed backbone
network. Connected to
this backbone are routers
which are in turn
connected to a particular
workgroup.

23. GEOGRAPHICAL ROUTING
Geographic routing( also called georouting
or positions-based routing)at is a routing
principle that relies on geographic position
information. It is mainly proposed for
wireless networks and based on the idea
that the source sends a message to the
geographic location of the destination
instead of using the network address.

24. FORWARDING TABLE SEARCH
ALGORITHMS
 In Unix operating system there is a routing table
which contains a certain number of tuples. These
tuples are consist of network IP,subnet mask,
gateway IP and interface name. These details are
used to forward a packet to connect to the
outside of its network to connect to the internet.
so this article gives an idea of how the
system takes the decision when a packet is
needed to be forwarded.

25. CONTINUE……..
Input:201.2.2.2
output: 12.23.44.1 eth9
here, there is no network ip entry in the
which starts with”201”. In this case it choose
default path(0.0.0.0,0.0.0.0,12.0.0) still, it will
perform bitwise and operate each entry and
then chooses default path and gateway to
send packet outside. Default interface to
which system is directly continue.

26. FORWARDING BASED ON LABEL
 The packet forwarding process at each router is based on
the concept of label swapping. This concept is similar to
what occurs t each asynchronous transfer mode(ATM)
switch in a permanent virtual circuit(PVC) .each MPLS
packet carries a 4-byte encapsulation header that contains
a 20-bit,fixed-length label arrive

27. MULTI-PROTOCOL LABEL SWITCHING
 Multiprotocol label switching(MPLS) is not a new
technology. It’s been around for several years. Many of
you must be flow the data is transmitted in the network
familiar with how the data is transmitted in the network
from from one place to another in the form of network
packets. These packets contain the source IP address and
the destination IP address .A packet is passed through
several routers contain the routing table which provides
the next-hop information to the packet finally reaches its
destination. This is how the IP forwarding works.

28. A NEW HEADER
 When you use the
platform label
space, the MPLS
ingress node places
labels in shim
header between the
link –layer header
and the
palyload.the shim
header includes the
following bits.

29. ROUTERS AS PACKET SWITCHES
 Packet switching is a
concept in computer
networking about how
data is transmitted over
the write. Router is a
server box(like any other
computer) that does
packet switching. A
switch however sits in the
layer below routers and
filters packets belonging
to a particular LAN
segments.

30. T
H
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