Address Resolution Protocol (ARP)

1. Address Resolution Protocol (ARP)

2. Internet and Data Link Layer Addresses • Each host and router on a subnet needs a data link layer address to specify its address on the subnet • This address appears in the data link layer frame sent on a subnet • For instance, 48-bit 802.3 MAC layer frame addresses Subnet DA DL Frame for Subnet

3. Addresses • Each host and router also needs an internet address at the internet layer to designate its position in the overall Internet 128.171.17.13 Subnet Subnet Subnet

4. Internet and Data Link Addresses Serve Different Purposes • Internet address (IP address) • To guide delivery to destination host across the Internet (across multiple networks) • Subnet Address • To guide delivery between two hosts, two routers, and a host and router within a single subnet • Single LAN, Frame Relay network, etc.

5. Analogy • In company, each person has a company-wide ID number (like IP address) • In company, person also has a physical office number in a building (like subnet address) • Paychecks are made out to ID numbers. • For delivery, also need to know office number

6. Address Resolution • Problem • Router knows that destination host is on its subnet based on the IP address • Does not know the destination host’s subnet address Destination Host 128.171.17.13 Subnet subnet address?

7. Address Resolution • Needs to know subnet address • IP packet is sent in data field of a subnet (data link layer) frame • Frame must have a subnet address (In Ethernet LAN, 48-bit MAC address) Subnet Frame IP Packet Subnet Destination Address

8. Address Resolution Protocol (ARP) • Router broadcasts an ARP-Request-PDU to all hosts on the subnet. • ARP Request in data field instead of IP packet • On a LAN, MAC address of 48 ones tells all stations to pay attention to the frame Subnet Frame ARPRequest-PDU Subnet DA= 48 ones

9. Address Resolution Protocol (ARP) • Router broadcasts an ARP Request message to all hosts on the subnet. • On a LAN, MAC address of 48 ones tells all stations to pay attention to the frame • Data link layer process in every host on the subnet listens, passes ARP request up to its internet layer process Subnet ARP Request

10. Address Resolution Protocol (ARP) • Host with IP address 128.171.17.13 responds • Sends ARP-Response-PDU • Response contains the destination host’s subnet address (48-bit MAC address on a LAN) ARP Response Subnet

11. Address Resolution Protocol (ARP) • Router can now deliver IP packets to the destination host • Places the IP packet in the subnet frame • Puts the destination host’s subnet address in the destination address field of the frame Deliver IP Packet within a subnet frame Subnet

12. The Internet of the Future • Problems Today • Problems in connecting when call • Congestion • Running out of 32 bit IP addresses • Security • Reliability

13. The Internet of the Future • Needs to Change • Commercial use cannot tolerate these problems • U.S. is no longer dominant. Cannot control management

14. Management of the Internet Today • IETF (Internet Engineering Task Force) • Creates standards • “Rough consensus and running code” • IAB (Internet Architecture Board) • Manages disputes within the IETF • Internet Society (ISOC) • Gets money to fund the IETF, IAB • Appoints IAB members

15. Requests for Comment (RFC) • IETF creates Internet (TCP/IP) Standards • Publications are called Requests for Comment (RFCs) • Listed by number (Original IP = RFC 731) • All RFCs are publicly available • About every 200th RFC is a list of which RFPs are official standards at that time

16. Management of the Internet Today • IANA (Internet Assigned Number Authority) • Controls the distribution of IP addresses • Controls the Domain Name System

17. Management of the Internet Today • IANA (Internet Assigned Number Authority) • Gives IP address blocks to three organizations • ARIN in North and South America and some parts of Africa • RIPE in Europe • APNIC in Asia • These in turn give blocks to large organizations and ISPs

18. Management of the Internet Today • IANA (Internet Assigned Number Authority) • Gives control of “root” domain names to other organizations • InterNIC has worldwide control of • .com, .net, .org • Various country agencies have control over country code roots • .UK, .AU, .JP, .CH

19. Changing Address Assignment • The Emerging Plan • Problem: IANA is U.S. government-funded • Replace IANA with an independent nonprofit agency • Internet Corporation for Assigned Names and Numbers (ICANN)

20. Changing Address Assignment • The Emerging Plan • ICANN will allow competition for the registration of .COM, etc. • ICANN will allow new top-level domain names because .COM is over-used

21. Long-Term Issues • Enforcement of rules • Especially in international context • Settlement charges among Internet backbone firms • Today, they carry one another’s traffic for free • Must work out payments for asymmetric traffic volumes • Enforcement of service conditions

22. IPv6 • Current version of the Internet Protocol is Version 4 (v4) • Earlier versions were not implemented • The next version will be Version 6 (v6) • No v5 was implemented • Informally called IPng (Next Generation) • IPv6 is Already Defined • Continuing improvements in v4 may delay its adoption

23. IPv6 • IPv6 will raise the size of the internet address from 32 bits to 128 bits • Now running out of IP addresses • Will solve the problem • But current work-arounds are delaying the need for IPv6 addresses

24. IPv6 • Improved Security • But, through IPsec, v4 is being upgraded in security as well • Improved Quality of Service (QoS) • But under IETF Differentiated Services (diffserv) initiative, IP v4 is being upgraded in this area as well

25. IPv6 • Improved Autoconfiguration • Can switch ISPs in the middle of a session • Automatic autoconfiguration much better than today’s standards in general • Piecemeal Deployment • Only some routers have to be upgraded • Others will still work but will not get new features

26. Multicasting • Traditionally, unicasting and broadcasting • Unicasting: send to one host • Broadcasting: send to ALL hosts • Multicasting • Send to SOME hosts • 500 stations viewing a video course • 50 computers getting software upgrades • Standards exist and are improving • Not widely implemented yet

27. Mobile IP • IP addresses are associated with fixed physical locations • Mobile IP is needed for notebooks, other portable equipment • Computer still gets a permanent, fixed location IP address • When travels, gets a temporary IP address at its location • This is linked dynamically to its permanent IP address

28. IP Telephony • Conduct telephone calls over the Internet or some other network that uses IP • Instead of using circuit-switched connections • Why? Reduce costs • Voice signals can be compressed • Voice signals can be multiplexed over trunk lines between routers

29. IP Telephony • Growing rapidly • Growing internal corporate use • Carriers are jumping in • May eventually replace traditional circuit-switched service

30. IP Telephony • Concerns • Congestion (Latency) on the Internet (not a major factor if PSDNs are used instead of the Internet) • Reliability. Computer networks are far less reliable than the public switched telephone network • Security • Technological maturity. Standards are still new.

31. Technology Test Beds • Small groups of organizations build advanced network • Link to Internet • Experiment with technology for tomorrow’s Internet • Speeds x10, x100, x1000 The Internet Technology Test Bed

32. Technology Test Beds • Internet2 • Collection of universities, vendors, and commercial firms • At least 10 Mbps to the desktop • 500 Mbps backbone speeds or faster • Multicasting • Advanced routing

33. Technology Test Beds • Internet2 • Member organizations connect at points called GigaPOPs (Gigabit points of presence) GigaPOP Organization GigaPOP Internet2 Organization GigaPOP