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CS 447 Networks and Data Communication

CS 447 Networks and Data Communication. ARP (Address Resolution Protocol) for the Internet. Department of Computer Science Southern Illinois University Edwardsville Fall, 2019 Dr. Hiroshi Fujinoki E-mail: hfujino@siue.edu. IP/000. Presentation Agenda. 1. What is ARP?

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CS 447 Networks and Data Communication

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  1. CS 447 Networks and Data Communication ARP (Address Resolution Protocol) for the Internet Department of Computer Science Southern Illinois University Edwardsville Fall, 2019 Dr. Hiroshi Fujinoki E-mail: hfujino@siue.edu IP/000

  2. Presentation Agenda 1. What is ARP? 2. Why ARP is needed? 3. How ARP works? 4. ARP extension to WAN/Internet CS 447 Networks and Data Communication Address Resolution Protocol (ARP) ARP/001

  3. 32-bit address ARP e.g. “146.163.147.59” (IP-MAC Translation) e.g. “1E:32:55:FF:3B:CC” 48-bit address CS 447 Networks and Data Communication Address Resolution Protocol (ARP): 1. It is a mechanism that translates MAC address to IP address IP (Internet Protocol) address (= software address) MAC (Medium Access Control) address (= hardware address) ARP/002

  4. CS 447 Networks and Data Communication 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) Example: Ethernet MAC address 2. Can not be changed ARP/003

  5. We can never change it! Source MAC Address Source MAC Address Frame Preamble Payload 6 bytes 6 bytes 8 bytes 64 - 1518 bytes MAC Frame CS 447 Networks and Data Communication What is MAC address?  It’s a hardware address associated to each NIC (usually hardwired in a ROM chip on a NIC)  The address used in Data-Link layer  Address deeply related to hardware

  6. MAC Address (48 bits) 4E 85 AA 00 00 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits Model # Serial # Vendor ID • 00 A0 24 – 3COM • 00 AA 00 -- Intel • 00 00 C0 -- SMC CS 447 Networks and Data Communication What is MAC address? How does it look like? 47 • 47 – EtherExpress16 • 4E 85 = 20101th card http://standards-oui.ieee.org/oui.txt http://www.coffer.com/mac_find/

  7. Application • The upper 5 layers use IP address Presentation • The lower two layers use MAC address Session Transport IP Address Network Logical Link MAC Address Physical NIC Network CS 447 Networks and Data Communication Host (a terminal computer) ARP/004

  8. NIC can understand ONLY hardware network address Application Presentation Session TCP/IP (IP address) (= software address) Transport Network ARP Logical Link Physical Ethernet (MAC Address) (= hardware address) CS 447 Networks and Data Communication Why ARP is needed? ARP/005

  9. How A can know MAC address of B? IP = 131.123.45.4 MAC = 1012 IP = 131.123.45.1 MAC = 1010 A B LAN Broadcast “ARP Search” message Sender IP “ARP Search” Receiver IP Sender MAC Broadcast MAC CS 447 Networks and Data Communication 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) ARP/007

  10. IP = 131.123.45.4 MAC = 1012 IP = 131.123.45.1 MAC = 1010 A B LAN “ARP Search” 1010 0000 131.123.45.4 131.123.45.1 Broadcast “polling” message Sender MAC Receiver IP Receiver MAC Sender IP “ARP Reply” Sender IP “ARP Search” Receiver IP Sender MAC Broadcast MAC “ARP Reply” 1012 1010 131.123.45.4 131.123.45.1 CS 447 Networks and Data Communication C ARP/008

  11. Host ARP entries will be cached LAN ARP ARP Cache CS 447 Networks and Data Communication If a host has to broadcast ARP search message for each packet, it is not efficient ARP/009

  12. How host A can know MAC address of B? CS 447 Networks and Data Communication ARP spanning more than one LAN: • Now we understand how ARP works for a LAN • How ARP can work for transmissions over more than one LAN? Routers do NOT forward broadcast messages (including “ARP search”) Router Host A Host B WAN/Internet Routers do NOT forward broadcast ARP Search message ARP/010

  13. Routers do NOT forward broadcast messages (including “ARP search”)

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