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CS 447 Networks and Data Communication
ARP (Address Resolution Protocol)for the Internet
Department of Computer ScienceSouthern Illinois University Edwardsville
Fall, 2015
Dr. Hiroshi FujinokiE-mail: [email protected]
IP/000
ARP/001
Address Resolution Protocol (ARP)
1. What is ARP?
2. Why ARP is needed?
3. How ARP works?
4. ARP extension to WAN/Internet
Presentation Agenda
CS 447 Networks and Data Communication
ARP/002
Address Resolution Protocol (ARP):
1. It is a mechanism that translates MAC address to IP address
MAC (Medium Access Control) address(= hardware address)
IP (Internet Protocol) address(= software address)
ARP (IP-MAC Translation)
e.g. “146.163.147.59”
32-bit address
e.g. “1E:32:55:FF:3B:CC”
48-bit address
CS 447 Networks and Data Communication
ARP/003
What are the software network address and hardware network address?
Software Network Address:
1. Network address managed by a network protocol
Example:(1) IP address in Internet Protocol (2) “computer name” in Microsoft NetBEUI
2. Network address you can change through OS
Hardware Network Address:
1. Network address “hardwired” in each NIC (assigned at a factory)
2. Can not be changed
Example: Ethernet MAC address
CS 447 Networks and Data Communication
ARP/004
Application
Presentation
Session
Transport
Network
Logical Link
Physical
IP Address
MAC Address
NIC
Network
Host (a terminal computer)
• The upper 5 layers use IP address
• The lower two layers use MAC address
CS 447 Networks and Data Communication
ARP/005
Why ARP is needed?
NIC can understand ONLY hardware network address
Application
Presentation
Session
Transport
Network
Logical Link
Physical
TCP/IP (IP address)(= software address)
Ethernet (MAC Address)(= hardware address)
ARP
CS 447 Networks and Data Communication
ARP/007
How ARP works?- Host A wants to send data to host B- Host A knows IP address of B (but not MAC address of B)
How A can know MAC address of B?
IP = 131.123.45.1MAC = 1010A IP = 131.123.45.4
MAC = 1012B
Broadcast “ARP Search” message
Sender IPSender MACReceiver IPBroadcast MAC“ARP Search”
LAN
CS 447 Networks and Data Communication
ARP/008
IP = 131.123.45.1MAC = 1010A IP = 131.123.45.4
MAC = 1012B
Broadcast “polling” message
Sender IPSender MACReceiver IPBroadcast MAC“ARP Search”
131.123.45.1“ARP Search” 1010131.123.45.40000
Sender IP Sender MAC Receiver IP Receiver MAC “ARP Reply”
131.123.45.1 1010131.123.45.4 1012 “ARP Reply”
LAN
C
CS 447 Networks and Data Communication
ARP/009
LAN
ARP
Host
ARP Cache
If a host has to broadcast ARP search message for each packet, it is not efficient
ARP entries will be cached
CS 447 Networks and Data Communication
ARP/010
ARP spanning more than one LAN:
• Now we understand how ARP works for a LAN
• How ARP can work for a connection spanning more than one LAN?
WAN/Internet
RouterHost A
Host B
Routers do NOT forward broadcast ARP Search message
How host A can know MAC address of B?
CS 447 Networks and Data Communication
