1 / 28

Classful Internet Addresses

Classful Internet Addresses. Chapter 4. Universal Identifiers. For our TCP/IP internet, we need an addressing scheme To hide the physical network details To give the appearance of one, big network Universal Communication Service Allows any host to communicate with any other

alexandra-york
Télécharger la présentation

Classful Internet Addresses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Classful Internet Addresses Chapter 4

  2. Universal Identifiers • For our TCP/IP internet, we need an addressing scheme • To hide the physical network details • To give the appearance of one, big network • Universal Communication Service • Allows any host to communicate with any other • Need a globally accepted method of identifying attached computers

  3. Host identifiers classified as: • Name: identify what an object is • Address: identify where it is • Route: Tell how to get there • Refer to successively lower levels of host identifiers • In general, • People prefer pronounceable names • Machines do better with compact representation • Standardized to compact, binary address

  4. Original Classful Scheme • Each host is assigned a 32-bit integer • Cleverly chosen to make routing efficient • Encode info about the network of the host • Prefix identifies a network • Each address is a (netid, hostid) pair • Each address is self-identifying • Quickly extract netid or host id

  5. What does an address specify? • Said “Address identifies a host” • Like the Hertz commercial (…not exactly!) • Consider a router connecting 2 networks • IP address has a netid and hostid • Can’t have single IP address (must have 2) • Multi-homed hosts • Computer with 2 or more connections IP ADDRESSES SPECIFY A CONNECTION TO A NETWORK (not an individual computer)

  6. Network & Broadcast Addressing • Encoded addresses make routing efficient • Also allows address to refer to networks as well as hosts • Hostid 0 refers to the network itself • Directed broadcast • Hostid of all 1’s (to all hosts of final router) • Due to error in Unix release, hostid of all 0’s is used, too • Has some valid netid • Powerful • Single packet from source (traveling the internet) • Delivered to all hosts on the destination network

  7. Limited broadcast • Broadcast aimed at the local network • Independent of the assigned IP address • Consists of 32 1’s • Host can use this as part of the startup • Before it learns its IP address • Before it learns the IP address for the local network • Once local network IP address is learned, directed broadcast should be used

  8. All-0s Address • Address of thirty-two 0 bits is reserved • Used when host needs to communicate • But does not yet know its IP address • Temporarily at startup • Host will have to obtain its IP address • Send a datagram via limited broadcast • Use address 0 to identify itself • Receiver understands host does not yet know its IP address • Uses a special method to send a reply

  9. Extension to Classful Addressing • Need unique network prefix for each network • In 1980’s, LANs caught on • Address space would soon be exhausted • Developed subnet addressing • Multiple physical networks share a prefix • In 1990’s, came up with supernetting • Classless addressing scheme • Allows prefix/suffix boundary to be arbitrary • Wait until chapter 9…..

  10. Multicast Addressing • Unicast: packet to single computer • Broadcast: packet to all computers on the network • Multicast: • Packet delivered to a subset of hosts • Class D of original scheme is reserved for this • Wait until chapter 16….

  11. Addressing Weaknesses • Addresses refer to network connection • If host computer moves, need new IP address • Bad for laptops! • Chapter 18 covers mobility problems • Chapter 22 covers DHCP • Growing pains • If a Class C network gets more than 255 hosts, must change to Class B address • No way to do gracefully

  12. Causes problems in routing • A host may have two connections • Path taken by packets to same host depends on the address used • Sometimes confusing to humans • Packets to same host will behave differently • Knowing only one IP address for the destination may not be enough

  13. Dotted Quad • 32-bit IP address: 10000000 00001010 00000010 00011110 is written as: 128.10.2.30 • With classful addressing: Class Lowest Address Highest Address A 1.0.0.0 127.0.0.0 B 128.0.0.0 191.255.0.0 C 192.0.0.0 223.255.255.0 D 224.0.0.0 239.255.255.255 E 240.0.0.0 255.255.255.254

  14. Not all possible addresses are used • In particular, 127.0.0.0 • In the Class A range • Reserved for loopback • TCP/IP testing • Inter-process communication on the local computer • When loopback address is the destination: • Protocol software in the computer processes it • Does not send across the network • Hosts and routers should not forward

  15. Summary of Special Addresses 1 2 2 2 3 1 – Invalid dest 2 – Invalid source 3 – Never appear on network

  16. Internet Addressing Authority • Network address prefixes must be unique • Private internet: • Whatever address prefixes you want • Connecting to global Internet: • Can’t duplicate other organizations • Network portion assigned by central authority

  17. Originally done by IANA • Internet Assigned Number Authority • Until fall 1998, Jon Postel ran the IANA • Late 1998 he died • Set up ICANN to take over the job • Internet Corporation for Assigned Names & Numbers • Addresses; names; other constants used in protocols • Usually not interact with central authority • Contact local ISP for prefix • Assigns network portion of addresses • Organizations assign suffixes to hosts as desired

  18. Reserved Address Prefixes • IBM has been assigned 9.0.0.0 • AT&T has been assigned 12.0.0.0 • Private internets can use these on their own networks • Usually not a good idea to use globally assigned prefixes • Most sites eventually connect to Internet • Prefixes have been reserved for private use (Chap 9)

  19. What classes are the networks?

  20. B A B What classes are the networks?

  21. Error in text: should be: 128.10.2.6 ISP9.0.0.0 Error in text: should be: 128.210.0.50

  22. Endianness (byte ordering) • Suppose 32-bit hexidecimal value 12345678 is stored in byte-addressable memory • Two ways to store it: MSB lowest LSB lowest (big-endian) (little-endian)

  23. Direct copying of bytes from one machine to another may change the data • Need a standard for byte-ordering • Must understand addresses, packet lengths, etc. • TCP/IP defines network byte order • Host or router converts binary items to the standard before sending a packet • Re-converts at the other end • User data is exempt; applications do as want • Send MSB first (big-endian)

  24. Summary • TCP/IP uses 32-bit IP addresses • Two parts: network prefix; host suffix • Original scheme used classes • A: _____ networks with up to _______ hosts/net • B: _____ networks with up to _______hosts/net • C:______networks with up to _______hosts/net (not counting reserved prefixes for private nets)

  25. IP addresses refer to network connections • Hosts with multiple connections have multiple IP addresses • Advantage: scheme allows addressing • A specific host • A network • All hosts on a network • Disadvantage: • May need to know multiple addresses for a multi-connected machine • TCP/IP protocols include byte-ordering standard

More Related