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  1. 1. AddressingThe ‘What’ and ‘Where’ ofCommunication
  2. 2. Addressing Addressing is necessary for any communication – To talk: Appearance, name, … – To call: Telephone numbers – To mail: Postal address – To visit: Postal address + directions – To E-Mail: E-Mail addresses – To instant message: ICQ#, AIM ID, etc. These ‘addresses’ allow us to uniquely identify the entity with which we wish to communicate
  3. 3. Addressing a la Shoch Name/Identifier: What – Names normally identify the entity – If an entity moves, the name/identity will remain the same Address: Where – Addresses identify the location of the entity – If an entity moves, the address will change Route: How to get there – Routes identify the path to get to an entity – If an entity moves, the route will change
  4. 4. Addressing Addressing deals with how to define an entity’s location (uniquely) Addressing is necessary for message delivery – An address is the start and end point for the route • However, routing is another subject – Where do we want the message to go?
  5. 5. Addresses We have already seen MAC addresses (for Ethernet and some other LANs): – e.g. 02-60-8C-08-E1-0C – 6 octet address – Globally unique – Defined statically by the hardware manufacturer Most people are familiar with the IP addresses used by TCP/IP networks: – e.g. – 4 octet address – Not necessarily globally unique – Defined dynamically by DHCP servers or negotiated by the operating system
  6. 6. IP AddressingA Closer Look
  7. 7. IP Addresses TCP/IP networks use IP for the network layer protocol IP defines 4 octet addresses – 4 billion possible addresses Usually written in the form A.B.C.D – A, B, C, and D are each 1 octet (0-255), normally written in decimal notation – Thus, IP addresses fall in the range: –
  8. 8. IP Addresses Originally intended for separate internets (interconnected LANs) – Thus, the 32 bit size was not a concern – 48 bits is generally considered a fairly safe size for globally unique addressing – Computers connected to ARPANET (and later incarnations) were just given consecutive addresses,,, …
  9. 9. IP Addresses Any computer connected to a TCP/IP network (e.g. the Internet) must have an IP address Further, any network interface card (NIC) using TCP/IP to access an network (e.g. the Internet) must have a different IP address
  10. 10. IP Addresses Even though there are 4 billion possible IP addresses, they are running out Here’s why: – Some of the bits are dedicated to header information (discussed later) • ½ the addresses for each lost bit – Addresses are categorized, and some of the categories are running out of addresses (while others are not)
  11. 11. Non-Classed Addresses Part of the address represented the network the computer resided on, and part represented the computer itself – Network: 7 bits (up to 128 networks) – Computer: 24 bits (up to 1.6 million computers on each network) Since there were very few networks on ARPANET originally, this wasn’t a problem
  12. 12. Address Classes When private organizations started joining the Internet, the needs became obvious – Some (fewer) networks have multitudes of computers (thousands) • e.g. The @Home network – Some (many) networks have very few computers (a few hundred or less) • e.g. The Windsor Police Department
  13. 13. Address Classes Quickly, the addresses were separated into 3 classes (plus room for more classes if needed): – Class A: Fewer networks, many nodes – Class B: Medium networks, medium nodes – Class C: Many networks, fewer nodes
  14. 14. IP Address Classes Class A:bit index: 0 1-7 8-31 0 network host (machine) Class B:bit index: 0 1 2-15 16-31 1 0 network host Class C:bit index: 0 1 2 3-23 24-31 1 1 0 network host
  15. 15. IP Address Classes Class A: – Range: – – Networks: 128 max, Machines: 65537-1.6 million – e.g. huge networks, such as large military/government organizations (e.g. FBI), the @Home network, etc… Class B: – Range: – – Networks: 16384 max, Machines: 257-65536 – e.g. Internet service providers (ISPs) (dial-up) Class C: – Range: – – Networks: 2 million max, Machines: 1-256 – e.g. Small businesses
  16. 16. IP Address Classes The IP address classes are self-identifying – Which means that given the address, you can determine what class an address is • Actually, using only the first number – Examples: • ( – 137 -> Class B • (@Home DHCP server) – 24 -> Class A
  17. 17. Other IP Address Classes Class D:bit index: 0 1 2 3 4-31 1 1 1 0 Multicast group address •These addresses are used to represent multicast groups •Discussed later Class E:bit index: 0 1 2 3 4 5-31 1 1 1 1 0 Reserved for future use •These addresses were left open to be used and divided into classes as needed
  18. 18. Special IP Addresses Used to indicate that this machine is without an assigned IP – Used during bootstrapping (e.g. requesting an IP from a DHCP server) <all 0s (binary)><hostID>: Used to send messages to some machine on this network Used to send broadcast messages across this machine’s network <netID><all 1s (binary)>: Used to send broadcast messages to the specified network Used to send messages back to this machine (called loopback or localhost)
  19. 19. IP Addressing Comments In IP addressing: – 0’s usually represent ‘this’ – 1’s usually represent ‘all’ Broadcasting, although discussed here in terms of addressing, will be discussed further
  20. 20. Loopback The address, does not normally exist on the network – Either as the source address or destination address of a packet The address is used internally by NICs – When a NIC receives a message addressed with to be transmitted, it passes the message directly to the receiver hardware – The receiver hardware returns the message to the operating system exactly as if the message were received from the network • However, the message never entered the network medium
  21. 21. Internal IP Addresses Depending on the address class needed by an organization, a range of internal addresses is available: – Class A: – – Class B: – – Class C: – IP routers outside a private (connection- shared) network, will not forward datagrams designated for addresses in these ranges
  22. 22. Multi-homed Machines There is no restriction preventing machines from participating in multiple networks – A machine could have multiple NICs – Each NIC would have its own MAC address – On TCP/IP networks, each of these NICs would be given a different IP address
  23. 23. Routers Routers are multi-homed machines – They have a number of network ports, each of which represents a different path Routers use tables that relate destinations to network paths – Internet routers relate destination network addresses with one of their network ports – When a datagram arrives at a router: • Its destination address is used to determine the network address • The network address is used to look up the destination port in the routing table
  24. 24. Network Addresses An IP address can be used to calculate the address of the network The machine address is passed through a filter (called a subnet filter): – This filter extracts the bits of the address that represent the network and sets the bits that represent the machine to zero – The filter determines which part of the address represent the network address, by using the subnet mask
  25. 25. Subnet Mask The subnet mask is a binary number, that has 0s in the machine portion of the address, and 1s in the network portion Most networks of each type use a constant subnet mask – Class A: (Binary: 11111111000000000000000000000000) – Class B: (Binary: 11111111111111110000000000000000) – Class C: (Binary: 11111111111111111111111100000000)
  26. 26. Using Subnet Masks Example: – Address: – Subnet Mask: 10001001110011110010000000000010Mask: 11111111111111110000000000000000Net Address: 10001001110011110000000000000000 Network address:
  27. 27. IPv6Next Generation Addressingin TCP/IP Networks
  28. 28. IPv6 Due to the limited nature of existing IP addressing (IPv4), a new version of IP addressing was developed This new scheme uses 16 octets for addresses, instead of 4 octets Written using hex notation:3A57:0000:0000:9CD5:3412:912D:6738:1928
  29. 29. IPv6 Features 16 octet addresses (128 bits) Larger numbers of address classes – More accurate control of network/machine counts Variable-sized headers – Optional information can be placed into the header when needed – Reduces header size in most cases Extendible protocol – IPv6 allows for new header information to be added to support different protocols
  30. 30. IPv6 Features Automatically reconfigurable – Addresses can be automatically reassigned dynamically – e.g. when a certain number of nodes join the network, a different address class may be desired Autoconfigurable – The use of autoconfiguration (such as DHCP) allows dynamic private addressing and dynamic public addressing
  31. 31. IPv6 Datagram Format optional header extension headers data
  32. 32. IPv6 Header Format0 4 12 31 version traffic class flow label32 48 56 63 payload length next header hop limit64 96 128 source address destination address
  33. 33. IPv6 Integration Will IPv6 replace IP addresses? – Who knows? Currently, temporary solutions have made IPv4 addresses capable of lasting longer than originally predicted If and when IPv6 is to be integrated, the process must be a transition – Closing the entire Internet down to convert hardware and software to IPv6 not going to happen – Some stations may take longer to transition than other stations • e.g. Bob’s Internet Shack vs. the Telus Network
  34. 34. IPv6 Integration NAT (network address translators) provide one example of such a temporary solution NATs provide three benefits: 1. NATs provide IP masquerading • Messages using these addresses pass through a network address translator (NAT) to be transformed into external IPs 2. NATs provide IP sharing • ISPs for example, have many customers, but significantly less at any given time are logged onto their system – IP addresses can be assigned dynamically to these customers when they log in 3. NATs provide schemes to allow networks to use either IPv4 or IPv6 – Addresses would be converted as they pass through a NAT
  35. 35. IPv6 Integration Another method that may be used for the transition between IPv4 and IPv6 is address inclusion: – IPv4 addresses could be embedded into IPv6 addresses • Translation between the two types of addresses is possible without any other information – Some problems exist with this approach, but in general it simplifies communication between IPv6 networks and IPv4
  36. 36. Special IPv6 Addresses 0:0:0:0:0:0:0:0 Used to indicate that this machine is without an assigned IP – Used during bootstrapping (e.g. requesting an IP from a DHCP server) 0:0:0:0:0:0:0:1 Used to send messages back to this machine (called loopback) – These two addresses are not valid on the actual network medium (same as with IPv4) 00:… Reserved (including IPv4 and IPX address inclusion) FF:… Multicast addresses