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Module 5.1: Internet Protocol

Module 5.1: Internet Protocol. TCP/IP Suite IP Addressing ARP RARP DHCP. Some Protocols in TCP/IP Suite. Address Types. Address Relations and Encapsulation. IP Addressing. IP address is 32 bits Originally had 2 level of hierarchy: network ID and host ID

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Module 5.1: Internet Protocol

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  1. Module 5.1: Internet Protocol • TCP/IP Suite • IP Addressing • ARP • RARP • DHCP K. Salah

  2. Some Protocols in TCP/IP Suite K. Salah

  3. Address Types K. Salah

  4. Address Relations and Encapsulation K. Salah

  5. IP Addressing • IP address is 32 bits • Originally had 2 level of hierarchy: network ID and host ID • The network ID is assigned by the Internet Network Information Center (InterNIC). • Routers use only network ID • Five classes of IP • Identify class by looking at the first byte • 0-127 gives A, 128-191 gives B, and 192 to 223 gives C • A gives 126 networks with 16 million hosts • B gives 16,382 networks with 64k hosts • C gives 2 million networks with 254 hosts K. Salah

  6. IP Addressing (Cont.) • IP addresses are written in dotted-decimal notations • Subnetting • Calss B address can support 64000 hosts! Hard to manage on a single network. • Adds another hierarchical level called the “subnet”. • Every host has its own IP address and its subnet mask. Hence, this host can determine, if a destination IP address is: • On its own subnet • On different subnet, but same own network • On different network K. Salah

  7. IP Addressing (Cont.) K. Salah

  8. Special Addresses • There are several IP addresses that are reserved for special purposes and are not available for assignment for hosts. • Any address with a first octet value of 127 is a loopback address. • A loopback address is used by a host to communicate with itself through TCP/IP. It is also used for testing and diagnostics. K. Salah

  9. Special Addresses (cont.) • 255 in either the host id or the network id designates a broadcast. • A message sent to 255.255.255.255 is broadcast to every host on the local network. A message sent to 196.1.64.255 is broadcast for every host on network 196.1.64. • 0 in both host id and network id can only appear as a source address in BOOTP protocol in bootstrapping when host is determining its own address. • Address Allocation for Private Intranets: • 10 A single Class A network. • 172.16 through 172.31 16 contiguous class B network • 192.168.0 through 192.168.255 256 contiguous Class C networks. • Any organization can use any address in these ranges without reference to any other organization. • Routers in networks do not use private addresses, e.g. ISP. Routers quietly discard all routing information regarding these addresses. • Hosts having only a private IP address do not have IP layer connectivity to the Internet. They have to go through NAT gateway. K. Salah

  10. ARP • How does a machine map an IP address to its Data Link layer (hardware or MAC) address? • This is needed by the source host (A) who needs to send an IP packet to another host (B) • if B is on same IP network as A, address frame to B • if B on a separate network, address frame to a router • TCP/IP solution: Address Resolution Protocol (ARP). See next figure. • ARP cache or table is used by hosts to avoid sending ARP request every time. ARP table entries age after a certain time (30 seconds). K. Salah

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  12. RARP • How does a diskless machine (X terminal) determine its IP address? • When bootstrap code starts execution on a diskless machine, it must use the network to contact a server to obtain the machine’s IP address • Usually, a machine’s IP address is kept on disk where OS finds it at startup • RARP is the protocol used to solve the reverse problem solved by ARP • Given a physical address, get the corresponding IP address • The RARP server must be located on the same physical network as the host. K. Salah

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  14. Encapsulation of ARP and RARP messages in Ethernet frames Note: The types above are unique. The length field is constant which is 2 bytes. The value of both types are more than 1500 bytes. K. Salah

  15. BOOTP and DHCP • A host requires three elements to connect to the Internet: • IP address • subnet mask • nearby router • BOOTP (Bootstrap Protocol) provided such information to hosts. • DHCP (Dynamic Host Configuration Protocol) builds on the capability of BOOTP. • DHCP is widely used because it provides a mechanism for assigning temporary IP addresses to hosts. • ISP uses DHCP to maximize the usage of their limited IP address space. • Typical messages used by DHCP: • DHCP Discover – broadcast initiated by host • DHCP Offer – reply by DHCP server(s) offering service to host • DHCP request – used by host to request info from a particular server. • DHCP ACK – reply by the selected server to host. K. Salah

  16. Passing of IP packet. K. Salah

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