CSCI 233 Internet Protocols Class 3

1. CSCI 233Internet Protocols Class 3 David C. Roberts

2. First…a little review

3. Internet Protocol Principles • Good Citizen Principle • Scarcest Internet Resource

4. Outline • Internet addresses • Mapping IP addresses to physical addresses

5. Internet addressing

6. The Internet • Is it a physical or virtual network? • It’s a virtual network, defined by protocols that run on hosts and routers. • Internet protocols make the Internet look like a world-wide uniform network, although it encompasses many networks that are very different from each other.

7. Internet Addresses • Each host connection on the Internet has a unique Internet address • The addresses are designed to make forwarding of Internet packets simple • An IP address has two parts: a prefix that identifies a network and a suffix that identifies a host on the network

8. Need for Control • To avoid conflicts in address use, some sort of authority is needed • It makes sense to assign addresses in blocks, not one at a time • ICANN (Internet Corporation for Assigned names and Numbers) oversees IP address assignment • Originally assigned in blocks of Class A, B and C addresses

9. Question • How many Internet addresses can one host have? • As many as it has network adapters 128.211.168.0/21

10. IPv6 Addressing • Each address is 128 bits • Enough addresses for every person on earth to have an internet with three times the addresses of the present Internet! • 1024 addresses per square meter of the earth’s surface

11. IPv6 Address Assignments

12. IPv4 to IPv6 Transition

13. IPv6 Address Split

14. IPv6 and MAC Addresses

16. IP Addresses

17. Functions of Internet Addresses • Provide a unique identification for a particular interface between a device and the network so that a datagram can be delivered to the correct recipient • Enable a path to be found across the Internet to reach the recipient, a process called routing

18. IPv4 Address • 32-bit integer, unique for each host on the network, used in all communication with the host • <IP address> ::= <netid> <hostid> • Netid: identifier of a network • Hostid: identifier of a host on the network

19. Dotted Decimal Notation 32-bit Internet address 10000000 00001010 00000010 00011110 Is written 128.10.2.30

20. Classes of IPv4 Addresses “Classful” addresses—types A, B and C below first 2 bits distinguish 3 primary classes Design of these classes is for efficient routing There have been other refinements—to discuss later

21. Class Determination Algorithm

22. Address Class Characteristics

23. Host Capacities

24. IP Address Split

25. Advantages of Classful Addressing • Simplicity and clarity—addresses and their setup are very easy to understand • Flexibility to accommodate different sizes of networks • Ease of separating host address for routing • Allows for reservation of some addresses for special purposes

26. Classless IPv4 Addressing • Temporary addressing scheme that does away with class A, B, C addresses • Network prefix can be any specified length • Forwarding techniques expanded to account for this: called Classless Inter-Domain Routing (CIDR)

27. Special IP Addresses

28. CIDR Slash Notation

29. Address resolution

30. IP and MAC Addresses • IP address is used to send datagrams across the Internet—that is, between networks, through routers • MAC address is used to deliver a frame of data within a single network • We send a datagram across the Internet with only an IP address • To deliver to a device at the destination network, a MAC address must be used

31. Local Delivery • The router at the destination network has the job of delivering the packet to the appropriate host • The router uses the local physical network to deliver to the local host • The local physical (MAC) address must be used, not the IP address

32. Address Resolution • The process of determining the physical address that corresponds to an IP address is called address resolution • Address resolution must occur at every network the packet encounters in its journey across the Internet

33. Resolution by Direct Mapping HA = f(IA)

34. Resolution by Dynamic Binding • ARP broadcasts a request packet • Host who has IP address in packet replies with physical address

35. ARP Caching • Broadcasting an inquiry is expensive • Every host must have a cache of recently acquired bindings • Results of ARP requests are cached • Before sending request, the cache is checked

36. ARP Cache Timeout • Responsibility for cache correctness is with the host maintaining the cache • Timeout value is set, and addresses from cache are not used if timeout value is exceeded • ARP performance is sensitive to the value of the timeout

37. Soft State • ARP cache is an example of “soft state” • Cache owner keeps record of acquired results, avoids cost of future inquiries • Cache is usually timed out to automatically remove stale values

38. ARP Refinements • Every ARP request has binding of source IP and MAC addresses • Since request is broadcast, all machines can extract sender’s IP to MAC address mapping and cache it • Most computers broadcast a gratuitous ARP request when they start up in case their mapping has changed

39. IPv6 ARP • Describe IPv6 ARP • There isn’t any!!!

40. IPv4 ARP Message Format Hardware type: 1 for Ethernet Protocol type: 0800 for IP addresses Xlen—length of physical and high-level addresses ARP exchanges involve filling in missing addresses 

41. IPv6 Neighbor Discovery • Neighbor is another computer on the same network • NDP allows an IPv6 host to discover all neighbors and routers upon startup • Early binding avoids delays when packets are transmitted

42. Conventions • 1’s refer to “all” • 0’s refer to “this” • Hostid=0 address refers to this network • Hostid=1’s broadcast to all hosts • Directed broadcast—netid of a specific network • Local broadcast—32 1’s—used at startup

43. Address Resolution • Physical addresses are used by hardware devices that can communicate directly (ie, MAC addresses on a LAN) • IP addresses create a massive virtual network • Network layer sends datagrams across the virtual network • Data link layer sends frames between physical devices

44. Need for Address Resolution

45. ARP • Each host has an Internet address, Ia • Each host also has a physical address, Pa • How to route packet to physical address, given its Internet address? • Two instances • Sending packets to routers, which have physical addresses • Sending packets to hosts, which have physical addresses

46. Direct Mapping Resolution • Choose a numbering scheme that makes address resolution efficient PA = f(IA) • If either P’s or I’s can be chosen, a correspondence can be established • Alternatively, lists of P-A pairs can be stored

47. Dynamic Binding Resolution ARP—Address Resolution Protocol • host A broadcasts packet with address IB • Asks host B to respond with PB • B recognizes the packet, responds with PB • A receives response, uses PB to send to B

48. ARP Cache • Cache of recently-acquired physical addresses is kept • ARP is used for packets after the first in a transmission • ARP cache times out after an interval • Example of “soft state”

49. ARP Refinements • Sender includes its own I to P binding in every ARP broadcast, so that receiving site, and others, can update ARP caches • Receivers update I to P binding in ARP cache before processing ARP packet

50. ARP Encapsulation