Brief History of the Internet

1. Brief History of the Internet • ARPA (Advanced Research Project Agency) – agency of the department of Defense. • In the 1960s funded universities and organizations to research the development of communication systems. • Let to the development of ARPANET – an experimental network that connected computer using packet switching. • Evolved in the Internet (capital I). • http://www.computerhistory.org/internet_history

2. Section 19.1 – Logical addressing • IP address is a 32-bit number usually written in the form w.x.y.z. For example, 143.200.139.98. • There are 128-bit address (IPv6) but we’ll defer those until later. • nslookup can be used to determine the address. • Also dig, host, named on Linux • Example: nslookupwww.uwgb.edu or nslookup www.google.com

3. Devices have a physical address (Ethernet) and an IP address (logical address). • Command ipconfig /all (PC command prompt) • Your IP address is given to you by your ISP and can change; • Network card determines the physical address. Won’t change unless you install a new card.

4. An IP address consists of a Netid and Hostid • Ex: Each campus computer has IP address 143.200.x.y • 143.200 is the network number. • x.y determined the device. • Advantage: • Routers outside the campus network need only know in which direction 143.200 is located rather than tracking every possible machine. • Once on campus, then the specific machine is identified.

5. Address classes for the early Internet • x’s define the Netid • y’s define the Hostid • Class A: 0xxxxxxx.yyyyyyyy.yyyyyyyy.yyyyyyyy • Class B: 10xxxxxx.xxxxxxxx.yyyyyyyy.yyyyyyyy • Class C: 110xxxxx.xxxxxxxx.xxxxxxxx.yyyyyyyy • Class D: 1110……multicast address…………….. • Class determined by the first few bits • Multicast (class D) identifies a group of hosts • Unicast identifies one (Class A, B, C) • 143.200 is a class B address since 14310 =1000 11112

6. Table 19.1 Number of blocks and block size in classful IPv4 addressing NOTE: Block means number of networks (globally) Block size is the number of hosts (devices) in a network

7. Classless addressing • Classful addressing too coarse for today’s needs. • Need more flexibility than just class A, B, or C addresses. • An organization needing 5000 addresses (way too large for a class C network) would be a class B network with ~65000 addresses. • Most would go unused.

8. Internet uses Classless Interdomain Routing (CIDR) • Left most n bits define the Netid, rightmost n-32 bits define the hostid. • Question: how does a router extract the Netid for forwarding?

9. Address mask • Collection of contiguous 1s followed by contiguous 0s • 1’s identify bits in the Netid; 0s the hostid • Alternative way to identify the Netid Table 19.2 Default masks for classful addressing

10. In general the notation x.y.z.t/n defines an IP address in which the leftmost n bits specify the Netid. • See ipconfig /all • Subnet mask = 255.255.192.0 = 1111 1111-1111 1111-1100 0000- 0000 0000 • Netid = logical AND of the IP address and mask • HostID = logical AND of the IP address and mask complement

11. Note that a 16-address block means an address mask of /28. • Host addresses differ ONLY in the rightmost 4 bits.

12. Supernetting • Combining smaller physical networks into a single larger one. • Could combine several class C networks into a single network.

13. Example Class C Network Bit Representation Address Range 211.195.8.0 11010011-11000011-00001000-xxxxxxxx 211.195.8.0 to 211.195.8.255 211.195.9.0 11010011-11000011-00001001-xxxxxxxx 211.195.9.0 to 211.195.9.255 211.195.10.0 11010011-11000011-00001010-xxxxxxxx 211.195.10.0 to 211.195.10.255 211.195.11.0 11010011-11000011-00001011-xxxxxxxx 211.195.11.0 to 211.195.11.255 • Address mask is 255.255.252.0 (11111111.11111111.11111100.00000000) All bits the same

14. Subnetting (reverse of supernetting): • Dividing a network into smaller networks • All hosts in a single subnet share the same subnet number. • Hosts and NetIDs are addressed consecutively • Number of addresses in a subnet is a power of 2.

15. Reasons to subnet • Separate different media (e.g. cable from optical fiber) • Separate devices that provide different functions such as various types of servers. • Security concerns • Better reflect the structure of an organization • Better manage network traffic

16. example • An organization is given a block of 64 addresses defined by 17.12.14.0/26. • This means it has 26=64 IP addresses. • It wants 3 subnets of size 16, 16, and 32. • Subnet mask for the larger subnet has twenty seven 1s followed by five 0s. • The smaller ones have a mask with twenty eight 1’s followed by four 0s • A possible arrangement is

17. Figure 19.7 Configuration and addresses in a subnetted network

18. Last 8 bits of the IP addresses, Net IDs underlined • 0000-0000 thru 0011-1111 (64 addresses) • Subnet 1: 0000-0000 thru 0001-1111 (32 addresses) • Subnet 2: 0010-0000 thru 0010-1111 (16 addresses) • Subnet 3: 0011-0000 thru 0011-1111 (16 addresses)

19. Example 19.10 on page 561.

20. A B LAN 192.168.0.2 internet 192.168.0.3 NAT-based router C 24.164.37.109 192.168.0.4 Addresses assigned by router Assigned by ISP NAT (Network address translation) based router: • If you all buy the same router from Best Buy, chances are your computers will ALL have the same IP address given to it by the router. • For example: • 192.168.x.x is a private address space.

21. Book covers a couple of designs; we’ll cover just their last one • Router has IP address • Each device behind the router has an IP address, BUT router hides them from the Internet world. • A packet sent from a device to the router contains a source IP address (w) and port # (x) • Router replaces them both with a fixed IP address (y) and another port # (z) and forwards packet to the internet. • Returning responses will be sent to y

22. Router maintains a table that relates (w, x) and (y, z) • Packet from Internet arrives at router; router looks up address in the NAT table • It substitutes and forwards the packet.

23. Advantages: • Hides IP addresses from Internet world • allows IP addresses to be reused • eliminates some tasks associated with managing subnets (NAT-based router does it) useful for home networks where consumer does not want to manage IP addresses • NAT-based router looks like a single device to the Internet world

24. Disadvantages: • Purists object to using port numbers to identify addresses (when they were designed to identify applications).Some see it as a kludge (pronounced klooj – nonstandard technique) to solve a problem that should be solved via IPv6 • other

25. IPv6 – section 19.2 but just the highlights • There are not enough IPv4 addresses • IPv6 uses a 128-bit address

26. Figure 19.14 IPv6 address in binary and hexadecimal colon notation

27. Figure 19.15 Abbreviated IPv6 addresses

28. Can specify • Registry: which agency registered the address (INTERNIC for north America, RIPNIC for Europe, APNIC for Asia and Pacific countries) • Provider: e.g. your ISP • Subscriber: e.g. a provider’s customer • Subnet: if the subscriber is an organization, it may have multiple subnets. • Node: the device.

29. IPv6 also provides • Security • Streaming support • Streamlined packets and more flexible packet headers for quicker routing • Authentication • It has been in the process of being phased in for years.

30. Section 20.1 Internetworking • Not a lot here, mostly setting the context and we’ve seen this before.

31. Figure 20.2 Network layer in an internetwork

32. Section 20.2 IPv4

33. Figure 20.4 Position of IPv4 in TCP/IP protocol suite

34. Figure 20.5 IPv4 datagram format

35. IP Packet (also a datagram) contents • See the book for most details but a couple of relevant things follow. • Source & destination addresses. • Time-To-Live (TTL) field – decremented by one each time a router forwards the packet. • When it is 0, it is discarded.

36. Checksum (on header only) – for error detection. • Needs to be recalculated at each router since the header can change. • Checksumming the header only is quicker • Higher level protocols will error check the dataif needed.

37. Fragmentation bits. • The IP protocol allows for the possibility that an IP packet might travel a network that forces an IP packet to divided into smaller pieces. • You can skip this section. • Priority bits – could allow a router to prioritize the packets it has in case of congestion . It was never really used. • Type of service (TOS) bits allow an app to request a type of handling.

38. Table 20.2 Default types of service

39. That same field also allows differentiated services – the ability of a router to examine this field and to determine the quality of service (QoS) expected of the higher layer. E.g. a file transfer or streaming real-time data. • Bits to define the protocol above IP using its services. • Allows the specification of a route to follow or to record the route taken.

40. Sections 20.3 and 20.4 deal with IPv6 and the transition from IPv4 to IPv6. • It’s not difficult reading but I won’t cover it. Be aware of the issues however.

41. Section 21.1 Address mapping • Will cover ARP (address resolution protocol) only – and only a general description of it.

42. The problem • Sender sends an IP packet across the Internet to a remote device. • Intermediate routers will route based solely on destination IP address. • The last router must deliver the IP packet directly to the device, most likely by embedding the IP packet into an Ethernet frame and sending it over the underlying LAN. • How does it determine the physical address?

43. ARP (Address Resolution Protocol). • Router sends a broadcast (containing the IP address) to all devices on a LAN. • Device associated with that IP address responds by sending its MAC address. • Router stores that info and then embeds the IP packet in a MAC frame and sends it. • The following diagram illustrates but I will not go into detail with regard to the ARP packet format or variations of this. It’s accessible to you based on what we’ve covered.

44. Figure 21.1 ARP operation

45. Chapter 22: Delivery, Forwarding, and Routing

46. Network Layer: Routing and IP • Problem • A network may be visualized as a graph • Find a route from S (source address) to D (destination address) • Does it matter which you choose?

47. An edge may have costs • Cost of a route = sum of edge costs • May just treat all edges the same (cost=1) • Cost of route = number of edges (number of hops)

48. Delivery: Section 22.1 • Direct delivery • Packet goes from one device to a destination located on the same physical network • Indirect delivery • Packet goes through multiple devices on its way to its destination. Devices are routers. • Last router is on the same physical network as the destination. From there, it’s direct delivery.

49. Forwarding: Section 22.2 • A router will: receive a packet and send it to some other router or to the destination. • Route method: • Either the router or packet contains the complete route • Can be used by some maintenance protocols to test routes, but not common. • Next Hop method • Router knows ONLY the next router (hop) in a path • Analogies to the US mail

50. In this case, the next node is along a “cheapest path”. • If all costs are 1, then cheapest is shortest. • Other criteria might be used