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IP topics

CS4550 Computer Networks II IP : internet protocol, part 1: history, basic function, names and addresses, ARP read Feit chapter 5 to 8. brief history (1) basic function (1) names and addresses (1) packet format (2) packet routing, routing tables (2)

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IP topics

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  1. CS4550 Computer Networks IIIP : internet protocol,part 1: history, basic function, names and addresses, ARPread Feit chapter 5 to 8

  2. brief history (1) basic function (1) names and addresses (1) packet format (2) packet routing, routing tables (2) lnternet Control Message Protocol (2) routing (calculation) : RIP, OSPF (2) IPv6 : the IP of the future (2) IP topics

  3. Internet : history • ARPAnet - 1st packet switched network, 1969 • Larry Roberts - packet switching, ARPAnet • BBN - built first IMPs • 1970s - ARPAnet grew rapidly • ethernet - PARC, Robert Metcalf 1970s • token ring, IBM - 1970s • TCP/IP - Vint Cerf - about 1980 • ref: Where wizards stay up late, Hafner and Lyon, Simon & Shuster

  4. IP : basic function • provides a connectionless, best-effort data delivery service to transport layer or applications. Packet delivery not guaranteed. • Makes use of underlying networks technologies (LANs, WANs). • interfaces between transport layer (TCP,UDP,etc.) and the network interface (ethernet, token ring, FDDI, WAN) --> IP is the “workhorse” of the Internet; the “glue” that connects many networks

  5. IP : basics • runs in routers (gateways, layer 3 switches) and hosts (end systems; computers). • routers are network switches which connect networks to other networks. (generally software). [aka gateways] • transport layer (TCP,UDP) - run in hosts only, not in routers. Interfaces to IP.

  6. TCP/IP internet ... TCP/IP IP IP WAN TCP/IP IP WAN IP TCP/IP

  7. TCP/IP protocol suite telnet, FTP, etc. apps TFTP, other apps. TCP UDP ICMP IP IGMP RARP ARP LAN/WAN media

  8. IP : names and addresses • need unique name for every host • hierarchical naming structure used • top level names assigned by InterNIC registration service (Herndon, VA) • lower level names assigned by organizations ex: cs.nps.navy.mil mil is the top level domain, assigned by InterNIC ; navy next level, nps next, etc.

  9. IP : names and addresses • some top level domains -- edu - colleges & universities gov - US fed. gov’t agencies com - commercial organizations in US net - internet service organizations org - non profit institutions mil - U S military countries --> jp, uk,fr, mx, de, etc.

  10. IP : names and addresses • name - series of labels, dots -- bellcore.com www.apple.com taurus.cs.nps.navy.mil • label can have up to 63 characters, and up to 255 characters in a name • worldwide naming tree -- root is top; domain is a node of the tree and its subtree

  11. IP : names and addresses • IP address : a 32 bit number, which is assigned to each “host” (computer) on an IP internet. • switching nodes in the internet - routers - also must have IP addresses. • the IP address actually is assigned to the interface point on the network, not the node itself .... analogous to street and house number for a home address

  12. IP : names and addresses • IP address - 2 main parts, netid and hostid • each part can be 1,2 or 3 bytes (class) • first few bits indicate which class applies • Class A : netid 1 byte, host id 3 bytes • Class B : 2 and 2 • Class C : 3 and 1 netid hostid

  13. IP : names and addresses • dotted decimal notation --> 131.120.1.60 • formats -> 0 (A), 10 (B), 11(C) ... in decimal, if 1st byte : 0-127 --> A, 128-191 --> B, 192-223 --> C. • additional classes : D, 224-239, for multicasting E, 240-255, reserved. • some address blocks reserved for networks not connected to the Internet

  14. IP : names and addresses • how many possible IP addresses, total? • how many class A net addresses exist? B? C? • how many hosts are possible for each class A? B? C? • is this an efficient method of assigning address classes in the Internet?

  15. IP : names and addresses • suppose your organization (eg, NPS) has a class B address; you don’t have 1 big network of 64K hosts; you have numerous smaller networks, mostly LANs. • further -- 65,000 is far too many hosts for a LAN or even a LAN internet, anyway.... • how these be separated into smaller, more manageable networks?

  16. IP : names and addresses --subnets • the host space can be divided further into a subnet part and a host part (or system part). • example: NPS is 131.120.X.Y.... we can make X (3rd byte) the subnet id, and the rest (4th byte) the host id. • This gives room for ~255 subnets of up to 255 hosts each.... “131.120.1” is one of the CS dept subnets...

  17. names and addresses : subnets 131.120.10 Divided into 4 LANS with Subnet mask 255.255.255.192 131.120.1 131.120.20 131.120.5 NPS: 131.120

  18. names and addresses : subnets • these different networks are connected by routers, and the NPS network is connected to the “outside” by a router. • how do the routers “know” which part is the subnet and hostid part? --> subnet mask - a 32 bit string of bits; 1s correspond to the netid part (network and subnet), 0s to the system (host) part IP AND SUBNETMASK = subnet address

  19. names and addresses : subnets some bit patterns are reserved for special purposes (e.g. broadcasting) , so --- 127.0.0.1 loopback 255.255.255.255 broadcast on local LAN • netid, hostid(subnetid) -- should not be all 0s or all 1s • netid, hostid(subnetid) -- must be at least 2 bits

  20. names and addresses : multihoming • recall that IP address has 2 parts, the netid and hostid • routers, and sometimes hosts, may be connected to more than one network; which netid is the correct one? --> both; the IP address corresponds to the network interface, not simply to the host itself. (think of a house on a corner....) • similarly, a host connected to 2 networks may be structured as a router

  21. names and addresses • IP runs on top of ethernet LANs, TR LANs, etc. These rout packets according to a different address, the MAC address (not the IP address). How can IP rout packets on these networks? --> must determine the MAC address which corresponds to a given IP address ARP, address resolution protocol

  22. ARP :address resolution protocol • purpose : obtain MAC (hardware) address of a machine, given its IP address. which MAC address has IP address 127.54.3.4? IP MAC

  23. ARP :address resolution protocol IP frame “fits” into the frame of the underlying network... (“wrapper”) IP frame MAC DA,SA INFO CSMA/CD frame

  24. ARP :address resolution protocol input : IP address, i ; output : MAC address, m; data structure : ARP table: list of (i,m) pairs; begin 1. search ARP table for i ; if found, return (m) else broadcast ARP request (i ); 2. wait for ARP reply (m); 3. when reply received, update ARP table (i,m) & return (m). end

  25. ARP :address resolution protocol • “broadcast request” - a LAN broadcast packet, contains the ARP packet (below) (field lengths shown in bytes) 2 2 1 1 2 6* 4 6* 4 lengths ARP msg type (request,reply) src/dest IP address src/dest MAC address IP/upper layer type ** ethernet length, may vary with other protocols MAC hardware type

  26. ARP :address resolution protocol • receiver part of ARP : upon receipt of an ARP request, if the destination IP address is MA (my address), then 1. update my ARP table, as appropriate, and 2. send ARP reply.

  27. Comments on ARP,Reverse ARP (RARP) • ARP - most systems allow system administrator to view table, make manual entries, or update table from file • Try : arp -a command from a school terminal • RARP • purpose : to find out ones own IP address, from the MAC address. Similar procedure. • useful for diskless workstations, however -- now being replaced by BOOTP and/or DHCP (dynamic host configuration protocol). These provide more info than RARP.

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