2. OBJECTIVES
What is OSI MODEL
What is Network layer in OSI MODEL
About ARP
Address resolution protocol
About Address Resolution
To make a distinction between logical address (IP address) and physical address (MAC
address).
To describe how the mapping of a logical address to a physical address can be static or
dynamic.
To show how the address resolution protocol (ARP) is used to dynamically map a logical
address to a physical address..
6. WHAT ADDRESS ?------ IP ADDRESSE
IP Addressing occurs at layer 2 (data link ) & layer 3 (network )of open system
interconnection (OSI) reference model .
layers (seven) specific particular network function such as addressing , for
control ,error control ,encapsulation and reliable message .
layer 2 addresses used for local /directly connected device.
7. WHAT ADDRESS ?------ IP ADDRESSE
Layer 3 addresses used for inter network /indirectly connected device.
Why How 48 Bit MAC Addresses
Media access protocol
To identify & group devices so that datagram transmition can be send and receive
8. Address Resolution Protocol (ARP)
Definition : Address Resolution Protocol (ARP) is
a protocol for mapping an Internet Protocol
address (IP address) to a physical machine
address(MAC address) that is recognized in the
local network. For example, in IP Version 4, the
most common level of IP in use today, an
address is 32 bits long.
9. How ARP Works
When an incoming packet destined for a host machine
on a particular local area network arrives at a gateway,
the gateway asks the ARP program to find a physical
host or MAC address that matches the IP address. The
ARP program looks in the ARP cache and, if it finds the
address
Server then creates data link Header & Trailer that
encapsulates packets & proceeds to transfer data
10. . If no entry is found for the IP address, ARP broadcasts a
request packet in a special format to all the machines on
the LAN to see if one machine knows that it has that IP
address associated with it. A machine that recognizes
the IP address as its own returns a reply so indicating.
ARP updates the ARP cache for future reference and
then sends the packet to the MAC address that replied.
How ARP Works
11.
12. In an Ethernet local area network, however, addresses for
attached devices are 48 bits long. (The physical machine
address is also known as a Media Access Control or MAC
address.) A table, usually called the ARP cache, is used to
maintain a correlation between each MAC address and its
corresponding IP address. ARP provides the protocol rules for
making this correlation and providing address conversion in
both directions.
Address Resolution Protocol (ARP)
13. Since protocol details differ for each type
of local area network, there are separate
ARP Requests for Comments (RFC) for
Ethernet, ATM, Fiber Distributed-Data
Interface, HIPPI, and other protocols.
How ARP Works
14. Address Resolution
Problem
Router knows that destination host is on its subnet based on
the IP address of an arriving packet
Does not know the destination host’s subnet address, so
cannot deliver the packet across the subnet
Subnet
128.171.17.13
subnet address?
Destination Host
16. ADDRESS MAPPING
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. These can be done
using either static or dynamic mapping.
17. ARP is Level 3 Protocol to perform…… Mapping
Map Addresses must be mapped to an IP addresses.
Some other layer 3 protocols (I)ARP (ii)Reverse ARP
(iii)Serial live ARP (iv)Inverse ARP.
Level 3 devices need ARP to map IP network address
to MAC hardware addresses so that IP packets come
be sent access network.
18. ARP is Level 3 Protocol to perform…… Mapping
Before datagram is send from 1 devices to 2nd. It
1ooks in its ARP cache to see if use is mac add and
corresponding IP addresses for destination device.
Only device with matching IP address replier to
sending device with packet containing mac address
for device.
19. ARP is Level 3 Protocol to perform…… Mapping
MAC address hardware addresses of host.
ARP maintains cache (table) in which MAC add are mapped
to IP address.
