The document discusses network layer protocols, focusing on the Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP) which are responsible for mapping IP addresses to MAC addresses and vice versa. It also covers the Dynamic Host Configuration Protocol (DHCP), which dynamically assigns IP addresses to clients, and the Internet Control Message Protocol (ICMP), which handles error reporting for the IP protocol. Overall, it highlights the importance of these protocols in ensuring effective communication across networks.

1. NETWORK LAYER PROTOCOLS

2. ARP

3. INTRODUCTION
Need of ARP and RARP
 The Internet is made of a combination of physical networks
connected by devices such as routers
 A packet from source host may pass through several different
networks and finally reaching the destination host
 At the network level the host and routers are recognized by their IP
addresses
 At the physical network the host and routers are recognized by
their MAC addresses(Physical Addresses)
 IP addresses are chosen by the local system administrator to suit the
local network
 Physical addresses are built into the interface hardware by the
manufacturer

4. INTRODUCTION
 The delivery of a packet to a host or a router requires two levels of
addressing: logical and Physical
 We need to be able to map a logical address to its corresponding
physical address and vice versa
 Mapping Logical to Physical Address
 Mapping Physical to Logical Address
 This can be done by using concept of Address resolution
 Address Resolution Protocol
 Reverse Address Resolution Protocol

5. ARP(ADDRESS RESOLUTION PROTOCOL )
 It is a protocol which is used to mapping the IP address(logical
address ) to MAC address(Physical or Ethernet address)
 ARP is usually considered to be a part of the data link layer

6. ARP IDEA

7. ADDRESS TRANSLATION WITH ARP
 ARP Request:
Argon broadcasts an ARP request to all stations on the network: “What is
the MAC Address of 128.143.71.1?
Argon
128.143.137.144
00:a0:24:71:e4:44
Router137
128.143.137.1
00:e0:f9:23:a8:20
ARP Request:
What is the MAC address
of 128.143.71.1?
ARP Request is Multicast

8. ADDRESS TRANSLATION WITH ARP
 ARP Reply:
Router 137 responds with an ARP Reply which contains the hardware
address
Argon
128.143.137.144
00:a0:24:71:e4:44
Router137
128.143.137.1
00:e0:f9:23:a8:20
ARP Reply:
The MAC address of 128.143.71.1
is 00:e0:f9:23:a8:20
ARP Reply is Unicast

9. ARP OPERATION
 A host or router needs to find the MAC Address of the another host or router
sends the ARP Request packet
 ARP Request packet contains the physical and IP address of the sender and IP
address of the receiver
 ARP request packet is broadcast to the network
 All hosts and router on the local network read the request
 The target host recognises the request for its IP address
 The target sends an ARP Reply packet containing its own physical address and
IP address (the other hosts need do nothing)
 The source gets the reply and reads out the target's physical address
 The source can now use that physical address to send IP packets

11. ARP REQUEST/REPLY FORMAT FIELDS
 Hardware Type field - Type of physical network (e.g., Ethernet)
 Protocol Type field - Higher-layer protocol (e.g., IP)
 HLen (“hardware” address length) and PLen (“protocol” address
length) fields - length of the link-layer address and higher-layer
protocol address, respectively
 Operation field - specifies whether this is a request or a response
 The source and target hardware (Ethernet) and protocol (IP)
addresses

12. ARP(ADDRESS RESOLUTION PROTOCOL )
 It is a protocol which is used mapping the MAC address (Physical or
Ethernet address) to IP address(logical address )
 Some hosts, such as mobile workstations(laptops), do not know their own
IP address when they are booted
 They only knows the MAC(physical) address saved in ROM
 They need IP address to communicate with the internet and create the
IP datagram
 They can use physical address to get the logical address
 The client host creates a RARP request and broadcast on the local
network
 RARP server exist on the network process the request and response with
available IP address(RARP Reply)

13. DYNAMIC HOST CONFIGURATION
PROTOCOL (DHCP)
 The RARP is almost out of date. It is replaced by two protocols
BOOTP and DHCP
 Dynamic Host Configuration Protocol (DHCP) is a protocol that
allows a server to dynamically distribute IP addressing and
configuration information to clients
 DHCP allows IP addresses to be “leased” for some period
of time
 DHCP assigns IP addresses for clients on demand
 DHCP relies on the existence of a DHCP server that is
responsible for providing configuration information to hosts

14. DYNAMIC HOST CONFIGURATION PROTOCOL
(DHCP)
DHCP operation
 To contact a DHCP server, a newly booted or attached host sends a
DHCP DISCOVER message to a special IP address (255.255.255.255)
that is an IP broadcast address
 This message will be received by all hosts and routers on that
network.(Routers do not forward such packets onto other networks,
preventing broadcast to the entire Internet)
 The server then reply to the host that generated the discovery message
by DHCP OFFER(all the other nodes would ignore it)
 Not possible to have one DHCP server on every network
 This still creates a potentially large number of servers that
need to be correctly and consistently configured.

15. DYNAMIC HOST CONFIGURATION
PROTOCOL (DHCP)
 Thus, DHCP uses the concept of a relay agent
 There is at least one relay agent on each network, and it is
configured with just one piece of information: the IP address of
the DHCP server
 When a relay agent receives a DHCPDISCOVER message, it
Unicast it to the DHCP server
 Then it get the DHCPOFFER response from the DHCP server and
send back to the requesting client

16. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45

17. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45 180.130.54.45
Here the black computer wants to register
itself on the network. So it sends a request
packet to the DHCP server requesting an
IP address

18. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
It broadcasts
DHCPDISCOVER msg
over local network with
dest address
255.255.255.255

19. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45

20. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
Agent will forward
the message from
black computer to
DHCP server

21. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
The request received from the
black system is processed by
DHCP server or agent. Others
ignore it.
DHCP contains a
pool of IP addresses
that can be leased
to hosts on demand

22. DHCP server
Ip address pool
Various scopes

23. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
Server sends available IP
address

24. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
Relay agent
pass the msg
from server to
the black
computer

25. DHCP
SERVER
RELAY
AGENT
160.50.50.1
160.50.50.2
160.50.50.3
Switch
180.130.54.45
180.130.54.45
Now the client has
a new ip adress. It
has to renew it
time to time.
160.50.50.4

27. INTERNET CONTROL MESSAGE PROTOCOL
VERSION 4 (ICMPV4)
Need of ICMP
 IP provides unreliable and connectionless datagram delivery
 The IP protocol has no error-reporting or error-correcting
mechanism
 What happens if something goes wrong? What happens if a
router must discard a datagram because it cannot find a router
to the final destination, or because the time-to-live field has a
zero value?
 The Internet Control Message Protocol (ICMP) has been designed
to compensate for the above two problems
 ICMP is a companion(friend) to the IP protocol
 ICMP defines a collection of error messages that are sent back to
the source host whenever a router or host is unable to process an IP
datagram successfully

28. POSITION OF ICMP IN THE NETWORK LAYER

29. ICMP ENCAPSULATION

31. General format of ICMP Messages

32. ICMP always reports error messages to the
original source.

33. ERROR REPORTING MESSAGES
Destination-unreachable messages
 When a host cannot deliver a datagram or router cannot route a
datagram, the datagram is discarded and they sends a Destination-
unreachable messages
 Destination-unreachable messages can be created by the destination
host and routers
Source-quench message
 It informs the source that a datagram has been discarded due to
congestion(jamming) in a router or the destination host
 The source must slow down the sending of datagrams until the
congestion is relieved

34. ERROR REPORTING MESSAGES
Time-exceeded Message
 When the final destination does not receive all of the fragments in a
set time, it discards the received fragments and sends a time-
exceeded message to the original source
Parameter-problem Message
 A parameter-problem message can be created by a router or the
destination host

35. TCP/IP
Protocol
Suite
35
Figure 9.10 Redirection concept
IP packet 1
RM
2
IP packet
3
IP packet
4
Error Reporting Messages

36. TCP/IP
Protocol
Suite
36
A redirection message is sent from a router
to a host on the same local network.
Note

37. QUERY MESSAGES
Echo-request and echo-reply Message
 An echo-request message can be sent by a host or router
 An echo-reply message is sent by the host or router that receives
an echo-request message.
 Echo-request and echo-reply messages can test the reach ability of a
host
 Echo-request and echo-reply messages can be used by network
managers to check the operation of the IP protocol.
Time stamp-request and time stamp-reply messages
 Timestamp-request and timestamp-reply messages can be used to
calculate the round-trip time between a source and a destination
machine even if their clocks are not synchronized.