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Presentation Title Subtitle Introduction to IP and Routing Author TM Copyright © 2002 OPNET Technologies, Inc. What is IP? • Connectionless, unreliable, best-efforts packet delivery system • Connectionless Just addresses a packet and sends it (analogous to mailing a letter) Does not need to create a connection to the destination. That is the responsibility of a higher layer (like TCP) • Unreliable Packets may be lost, delayed, duplicated, out of order, or damaged in transmission Up to higher layer to provide reliability • Best-efforts Packets will not be discarded arbitrarily, without good cause • Exhaustion of resources • Failure of lower layer Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 2 OSI vs. TCP/IP • The TCP/IP protocol stack does not match the OSI protocol stack exactly • TCP/IP in use before OSI protocols appeared • ARPANET (research network sponsored by DoD) needed Ability to connect multiple networks together Ability to survive loss of subnet hardware, with no connection loss • Internet layer developed: Can inject packets that travel independently to the • destination One of the first implementation by Berkeley Good implementation Free Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 3 OSI vs. TCP/IP, cont. • OSI model developed before any implementation • TCP/IP model developed after it was implemented • Some companies already had product with TCP/IP • Did not want to support 2 protocols • OSI more complex than TCP/IP Q: What do you get when you cross a mobster with an international standard? A: Someone who makes you an offer you can’t understand • Waited to see how others would use OSI • TCP/IP became more widespread, while nothing really happened with OSI • OSI still used as a first example of a layered protocol stack Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 4 OSI and TCP/IP stacks Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 5 IP Addresses • IP addresses are analogous to postal addresses • Destination is described from the general to the specific Zip code/State -> City -> Street -> Building -> Person Network Address -> Host Address • IP Addresses consist of 4 numbers, separated by periods • Each number ranges from 0 – 255 • Examples: 12.221.14.2 192.15.223.111 • Each machine on a network has a unique IP Address • Numbers assigned by the Network Information Center (NIC) Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 6 IP Addresses Classes • Address classes • Class A: 1.0.0.0 to 127.255.255.255 126 networks with 16 million hosts each • Class B: 128.0.0.0 to 191.255.255.255 16,382 networks with 64K hosts each • Class C: 192.0.0.0 to 223.255.255.255 2 million networks with 254 hosts each • Class D: (multicast) 224.0.0.0 to 239.255.255.255 • Class E: 240.0.0.0 and up: reserved for future use • 127.xx.yy.zz is a “loopback” address Not actually sent on the wire Processed locally, as an incoming packet Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 7 IP Subnets • Subnets are used if you have more machines than IP addresses • Allows a network to be split into several parts for internal use, but still act like a single network to the outside world • IP packets are routed depending on their destination • Other network: forwarded to next router • This network: forwarded to internal destination • Uses “Subnet Mask” to determine internal destination Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 8 Dynamic Host Configuration Protocol • Alternative to “static” IP Addresses • Allows for even more hosts within a subnet • Major downfall is that you cannot host a service easily Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 9 Host names • Familiar names are easier to remember than IP Addresses • Names can be registered (internic) • .net, .com, .gov, .au, .fr, etc • e.g. www.amazon.com, www.opnet.com • “Ping” a host name to get its IP Address Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 10 Domain Name System (DNS) • A DNS server keeps track of the meaning of host and domain names • Even without DNS, you can get to other internet locations, using the IP Address Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 11 IP Quality of Service (QoS) • Some applications require different service than others • Considerations: • Connection establishment delay • Connection establishment failure probability • Throughput • Transit delay • Residual error ratio • Protection • Priority • Delay variation Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 12 IP Security (IPsec) • Developing standard for security at the network layer • Earlier security approaches have inserted security at the application layer • Useful for implementing • Virtual Private Networks (VPNs) • Remote user access through dial-up connection to private networks • Security arrangements can be handled without requiring changes to individual user computers. • Cisco has been a leader in proposing IPsec as a standard (or combination of standards and technologies) and has included support for it in its routers Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 13 IPv6 Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 14 IP Routing • Many different routing algorithms • Static • Routes decided in advance • Not adaptive to network changes • Dynamic • Change routing decisions to reflect changes in topology and traffic • Adaptive to network changes Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 15 Static Routing • Manually assign routes to destinations • Flooding Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 16 Dynamic Routing • DistanceVector • Each router maintains a table giving Best known distance to each destination Which line/interface to use • Tables updated by exchanging with neighbors Bellman-Ford is most well-known algorithm Was the original ARPANET routing algorithm Used by RIP on the internet Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 17 Dynamic Routing, cont. • Link State routing • Discovers neighbors and addresses • Measures cost to neighbor Delay Queue size Bandwidth Etc • Creates a packet with all of this info • Sends packet to all other routers • Computes shortest path to every other router • Table can become quite large Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 18 Hierarchical Routing • Not every possible destination needs to be known by every router • Routers within a subnet • May only need to know internal destinations • Needs to also know “border” routers to get to the outside Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 19 Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 20 Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 21 Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 22 Copyright © 2002 OPNET Technologies, Inc. <Class_Title> - 23