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ICS 156: Lecture 2 (part 1)

ICS 156: Lecture 2 (part 1). Today: IP addressing Data link protocols and ARP Notes about lab. IP Addressing. Addressing defines how addresses are allocated and the structure of addresses IPv4 Classful IP addresses (obsolete)

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ICS 156: Lecture 2 (part 1)

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  1. ICS 156: Lecture 2 (part 1) Today: IP addressing Data link protocols and ARP Notes about lab

  2. IP Addressing • Addressing defines how addresses are allocated and the structure of addresses • IPv4 • Classful IP addresses (obsolete) • Classless inter-domain routing (CIDR) (RFC 854, current standard) • IP Version 6 addresses

  3. What is an IP Address? • An IP address is a unique global address for a network interface. • An IP address uniquely identifies a network location. • Routers forwards a packet based on the destination address of the packet. • Exceptions: • DHCP and NAT (lab 7)

  4. IP Addresses

  5. 32 bits 0x4 0x5 0x00 44 10 9d08 010 0000000000000 2 2 128 0x06 8bff 10 128.143.137.144 128.143.71.21 IP Addresses

  6. An IP address is often written in dotted decimal notation • Each byte is identified by a decimal number in the range [0..255]: 10000000 10001111 10001001 10010000 1st Byte = 128 2nd Byte = 143 3rd Byte = 137 4th Byte = 144 128.143.137.144

  7. Structure of an IP address 31 0 • An IP address encodes both a network number (network prefix) and an interface number (host number). • network prefix identifies a network • the host number identifies a specific host (actually, interface on the network). network prefix host number

  8. How long the network prefix is? • Before 1993: The network prefix is implicitly defined (class-based addressing) • After 1993: The network prefix is indicated by a netmask.

  9. Before 1993: Class-based addressing • The Internet address space was divided up into classes: • Class A:Network prefix is 8 bits long • Class B:Network prefix is 16 bits long • Class C:Network prefix is 24 bits long • Class D is multicast address • Class E is reserved

  10. Classful IP Adresses (Until 1993) • Each IP address contained a key which identifies the class: • Class A:IP address starts with “0” • Class B:IP address starts with “10” • Class C:IP address starts with “110” • Class D:IP address starts with “1110” • Class E:IP address starts wit “11110”

  11. The old way: Internet Address Classes

  12. The old way: Internet Address Classes

  13. Problems with Classful IP Addresses • Fast growing routing table size • Each router must have an entry for every network prefix • ~ 221 = 2,097,152 class C networks • In 1993, the size of routing tables started to outgrow the capacity of routers

  14. Other problems with classful addresses • Address depletion for large networks • Class A and Class B addresses were gone • How many class A/B network prefixes can there be? • Limited flexibility for network addresses: • Class A and B addresses are overkill (>64,000 addresses) • Class C address is insufficient (256 addresses)

  15. Classless Inter-domain routing (CIDR) • Network prefix is of variable length • Addresses are allocated hierarchically • Routers aggregate multiple address prefixes into one routing entry to minimize routing table size

  16. CIDR network prefix is variable length 144 137 128 143 • A network mask specifies the number of bits used to identify a network in an IP address. Addr 10000000 10001111 10001001 10010000 255 255 0 255 Mask 11111111 11111111 1111111 00000000

  17. CIDR notation • CIDR notation of an IP address: • 128.143.137.144/24 • /24 is the prefix length. It states that the first 24 bits are the network prefix of the address (and the remaining 8 bits are available for specific host addresses) • CIDR notation can nicely express blocks of addresses • An address block [128.195.0.0, 128.195.255.255] can be represented by an address prefix 128.195.0.0/16 • How many addresses are there in a /x address block? • 2 (32-x)

  18. CIDR hierarchical address allocation 128.0.0.0/8 • IP addresses are hierarchically allocated. • An ISP obtains an address block from a Regional Internet Registry • An ISP allocates a subdivision of the address block to an organization • An organization recursively allocates subdivision of its address block to its networks • A host in a network obtains an address within the address block assigned to the network ISP 128.195.0.0/16 128.1.0.0/16 128.2.0.0/16 University 128.195.4.150 Foo.com Bar.com CS Library 128.195.1.0/24 128.195.4.0/24

  19. Hierarchical address allocation 128.195.4.0 128.195.4.150 128.195.4.255 • ISP obtains an address block 128.0.0.0/8  [128.0.0.0, 128.255.255.255] • ISP allocates 128.195.0.0/16 ([128.195.0.0, 128.195.255.255]) to the university. • University allocates 128.195.4.0/24 ([128.195.4.0, 128.195.4.255]) to the CS department’s network • A host on the CS department’s network gets one IP address 128.195.4.150 128.0.0.0 128.255.255.255 128.196.255.255 128.195.0.0

  20. I 128.0.0.0/8 ISP1 CIDR allows route aggregation You can reach 128.0.0.0/8 via ISP1 • ISP1 announces one address prefix 128.0.0.0./8 to ISP2 • ISP2 can use one routing entry to reach all networks connected to ISP1 128.0.0.0/8 ISP3 ISP1 128.1.0.0/16 128.2.0.0/16 128.195.0.0/16 University Foo.com Bar.com CS Library

  21. CIDR summary • A network prefix is of variable length: a.b.c.d/x • Addresses are hierarchical allocated • Routers aggregate multiple address prefixes into one routing entry to minimize routing table size.

  22. 204.1.0.0/16 ISP1 128.0.0.0/8 ISP1 What problems CIDR does not solve (I) You can reach 128.0.0.0/8 And 204.1.0.0/16 via ISP1 • An multi-homing site still adds one entry into global routing tables ISP3 ISP1 ISP2 128.0.0.0/8 204.0.0.0/8 204.1.0.0/16 Mutil-home.com 204.1.0.0/16

  23. 204.1.0.0/16 ISP1 What problems CIDR does not solve (II) You can reach 128.0.0.0/8 And 204.1.0.0/16 via ISP1 • A site switches provider without renumbering still adds one entry into global routing tables ISP3 ISP1 ISP2 128.0.0.0/8 204.0.0.0/8 128.0.0.0/8 ISP1 204.1.0.0/16 Switched.com 204.1.0.0/16

  24. Global routing tables continue to grow Source: http://bgp.potaroo.net/as6447/

  25. Special IP Addresses • Reserved or (by convention) special addresses: Loopback interfaces • all addresses 127.0.0.1-127.255.255.255 are reserved for loopback interfaces • Most systems use 127.0.0.1 as loopback address • loopback interface is associated with name “localhost” Broadcast address • Host number is all ones, e.g., 128.143.255.255 • Broadcast goes to all hosts on the network • Often ignored due to security concerns • Test / Experimental addresses • 10.0.0.0 - 10.255.255.255 • 172.16.0.0 - 172.31.255.255 • 192.168.0.0 - 192.168.255.255 • Convention (but not a reserved address) Default gateway has host number set to ‘1’, e.g., 128.195.4.1

  26. IP Addressing • Addressing defines how addresses are allocated and the structure of addresses • IPv4 • Classful IP addresses (obsolete) • Classless inter-domain routing (CIDR) (current standard) • IP Version 6 addresses

  27. IPv6 - IP Version 6 • IP Version 6 • Designed to be the successor to the currently used IPv4 • Specification completed in 1994 • Makes improvements to IPv4 (no revolutionary changes) • One (not the only !) feature of IPv6 is a significant increase in of the IP address to 128 bits (16 bytes) • IPv6 will solve – for the foreseeable future – the problems with IP addressing • 1024 addresses per square inch on the surface of the Earth.

  28. IPv6 Header

  29. IPv6 vs. IPv4: Address Comparison • IPv4has a maximum of 232 4 billion addresses • IPv6 has a maximum of 2128 = (232)4  4 billion x 4 billion x 4 billion x 4 billion addresses

  30. Notation of IPv6 addresses • Convention: The 128-bit IPv6 address is written as eight 16-bit integers (using hexadecimal digits for each integer) CEDF:BP76:3245:4464:FACE:2E50:3025:DF12 • Short notation: • Abbreviations of leading zeroes: CEDF:BP76:0000:0000:009E:0000:3025:DF12  CEDF:BP76:0:0:9E :0:3025:DF12 • “:0000:0000:0000” can be written as “::” CEDF:BP76:0:0:FACE:0:3025:DF12  CEDF:BP76::FACE:0:3025:DF12

  31. IPv4 address in IPv6 • IPv6 addresses derived from IPv4 addresses have 96 leading zero bits. • Convention allows to use IPv4 notation for the last 32 bits. ::80:8F:89:90  ::128.143.137.144

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