CIM 2465 Intro to TCP/IP1 Introduction to TCP/IP (Topic 5) Textbook: Networking Basics, CCNA 1 Companion Guide, Cisco Press Cisco Networking Academy Program, CCNA 1 and 2, Companion Guide, Cisco Press, Latest Edition

CIM 2465 Intro to TCP/IP2 TCP/IP Model TCP/IP was first developed as part of a contract from the US DoD OSI ModelTCP/IP Model Application PresentationApplication Session Transport NetworkInternet Data Link PhysicalNetwork Access

CIM 2465 Intro to TCP/IP3 TCP/IP Network Access Layer (1) Also known as Network Interface Layer Defines how computers and networking devices should access a physical medium to send bits to others Match OSI Layers 1 and 2 Does not actually define any network access layer standards, but refers to other well-defined standards Note that ARP, proxy ARP, and RARP mainly work at TCP/IP’s internet layer, but they provide an interface to the network access layer

CIM 2465 Intro to TCP/IP4 TCP/IP Network Access Layer (2) Fig 9-2

CIM 2465 Intro to TCP/IP5 TCP/IP Internet Layer Defines how to deliver data from one host to another (over multiple different physical networks) By separating its logic from the underlying networking details, thus allows hosts, networking devices, routers, to use the same processes and logic regardless of the underlying physical networks being used Logical Addressing (IP addresses for each network interface) Routing Defines several protocols, most important being the Internet Protocol (IP)

CIM 2465 Intro to TCP/IP6 Key Internet Layer Protocols ProtocolDescription Internet Protocol (IP)Defines routing, logical IP addressing, the format of IP headers and packets, and interfaces Address Resolution Protocol (ARP) Defines the process by which an IP host dynamically learns the mapping between another host’s IP address and its MAC address Reverse Address Resolution Protocol (RARP) Mostly unused today. Provides a basic method for IP address assignment Internet Control Message Protocol (ICMP) Defines messaging used to manage and control IP (e.g. used by the command ping)

CIM 2465 Intro to TCP/IP7 Basic IP Routing IP routing defines how to forward data, in form of IP packets, from one host to another Fig 9-3

CIM 2465 Intro to TCP/IP8 IP Packets An IP packet is the header defined by the IP protocol, along with any higher-layer protocol headers and the end-user data Basic IP Packet format IP HeaderTCP/IP Transport & Application Layer Headers End-user data

CIM 2465 Intro to TCP/IP9 How IP Routing uses IP Addresses Routers use IP routing tables to tell them out which interfaces to forward packets To make routing efficient –IP addresses for hosts on the same physical network must have the same value in the first part of the addresses (network address) –Each group then need one entry in the routing table Fig 9-5

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CIM 2465 Intro to TCP/IP11 TCP/IP Transport Layer To provide the service of taking data from one application process on one computer and delivering that data to the correct application process on another computer Compare with the Internet Layer, the internet layer delivers data packets from one computer to another, but it does not think about which application sent the data or which application on the receiving computer needs the data

CIM 2465 Intro to TCP/IP12 Fig 9-6 Two main Transport Layer protocols –Transmission Control Protocol (TCP) –User Datagram Protocol (UDP)

CIM 2465 Intro to TCP/IP13 TCP Vs UDP Transport Layer Feature DescriptionTCPUDP Segmentation of data Breaking large chunks of data into network-legal sizes, call segments YN Multiplexing using port numbers Identifying application process (by port) that needs the data YY Error recoveryMonitoring for lost segments and resending them YN In-order delivery of data Monitoring received segments and putting them in correct order YN Flow controlMonitoring network performance and control the flow of data YN

CIM 2465 Intro to TCP/IP14 TCP/IP Application Layer Provides services to applications Fig 9-7

CIM 2465 Intro to TCP/IP15 Application Layer Protocols ProtocolDescriptionTransport Layer Protocol Hypertext Transfer Protocol (HTTP) Defines the commands, headers, and processes by which web servers and web browsers transfer files TCP Trivial File Transfer Protocol (TFTP) A very simple protocol that allows file transfer UDP File Transfer Protocol (FTP) A very robust protocol used for transferring files TCP

CIM 2465 Intro to TCP/IP16 Application Layer Protocols ProtocolDescriptionTransport Layer Protocol Network File System (NFS) A distributed file system protocol suite that allows remote file access across a network UDP Simple Mail Transfer Protocol (SMTP) Defines the process by which my be forwarded and then held for later retrieval TCP Terminal Emulation (Telnet) Defines the protocols used to allow a user to remotely access another computer TCP

CIM 2465 Intro to TCP/IP17 Application Layer Protocols ProtocolDescriptionTransport Layer Protocol Simple Network Management Protocol (SNMP) An application protocol usually used by the network management software to allow a network engineer to monitor and troubleshoot network problems UDP Domain Name System (DNS) A protocol that defines how a computer may refer to another computer by name, instead of the IP address UDP Dynamic Host Configuration Protocol (DHCP) A protocol used to dynamically assign IP addresses to hosts UDP

CIM 2465 Intro to TCP/IP18 TCP/IP Internetworks

CIM 2465 Intro to TCP/IP19 Routing Fundamentals Routers have two main functions –Perform end-to-end delivery of IP packets from the sending host to the receiving host. Receive packets Decide to which router or host to send the packets next Forward them –Maintain a Routing Table with the best routes to reach each possible destination, using some routing protocols

CIM 2465 Intro to TCP/IP20 IP Routing (1) Layer 2 devices, such as LAN switches, can forward data on only Ethernet links (within the same network), it cannot connect to WAN links (to other networks), as the physical and datalink standards are different Routers, can connect to multiple types of physical network (internetworking) So, routers can receive IP packets sent by computers and send the packets over any physical networks, to deliver the packets to the destinations. This forwarding process is called IP routing or IP forwarding

CIM 2465 Intro to TCP/IP21 IP Routing (2) A router examines incoming packets, looks at the destination IP address, and decides out which interface to forward the packet Routing process relies on each router knowing how to route IP packets based on its IP routing table Routers use routing protocols (e.g. RIP, EIGRP), to dynamically learn the required routes

CIM 2465 Intro to TCP/IP22 Some Key Terms Routing / Forwarding –The process of received packets, deciding where to forward them next, and forwarding them Routed protocol / Routable protocol –A protocol that defines a packet that can be forwarded by a routing process –E.g. IP, IPX (Netware) are routable, NetBEUI is non- routable Routing protocol –A protocol used between routers so that they can dynamically learn routes to add to their routing tables

CIM 2465 Intro to TCP/IP23 Routing between Two Connected LAN Subnets The router has an interface physical attached to each of the two LANs

CIM 2465 Intro to TCP/IP24 IP-Centric Perspective No changes to source and destination IP address

CIM 2465 Intro to TCP/IP25 Note that the router will remove the Ethernet header/trailer and encapsulate a new one Note the changes of MAC addresses

CIM 2465 Intro to TCP/IP26 IP Routing: Host Perspective (1)

CIM 2465 Intro to TCP/IP27 IP Routing: Host Perspective (2) Decision –If the destination IP address is on my same IP network/subnet, send the packet directly to that host –If the destination IP address is not on my same IP network/subnet, send the packet to my default router (default gateway)

CIM 2465 Intro to TCP/IP28 Main steps of IP routing P.400 of the textbook

CIM 2465 Intro to TCP/IP29 More Detailed Routing Steps

CIM 2465 Intro to TCP/IP30 Perspectives on WAN Routing R1, R2 configured to use Serial interface and a data link protocol PPP (Point-to-Point Protocol)

CIM 2465 Intro to TCP/IP31 Important Characteristics of IP IP is Unreliable –The protocol does not attempt to perform any error recovery of data (lost data) –How to have Reliable transmission Uses TCP transport layer protocol, which performs error recovery The application itself performs the error recovery IP is Connectionless

CIM 2465 Intro to TCP/IP32 Connectionless Vs Connection-oriented Connectionless –The sender and receiver do not pre-arrange for communication to occur –E.g. IP, Ethernet, UDP –Analogy: mailing a letter Connection-oriented –The sender and receiver must pre-arrange for communication to occur –E.g. TCP, Frame Relay –Analogy: make a phone call

CIM 2465 Intro to TCP/IP33 Full IP Header Table 10-4 for details

CIM 2465 Intro to TCP/IP34 Routing Protocols Used by routers to learn routes When a collection of routers uses the same IP routing protocol, the routers exchange messages and update their own routing tables HOW? –Connected subnets –Static Routes –Routing protocols

CIM 2465 Intro to TCP/IP35 Learning Connected Routes Subnets to which a router’s interfaces are connected are called connected subnets Routers automatically add routes to their IP routing tables for directly connected subnets means “Connected”

CIM 2465 Intro to TCP/IP36 Static Routes Add routes to routing tables via router configuration E.g. a Cisco router command to R1 (interface FA0/1) of Fig ip route will add an entry to R1 S Fa0/ (S means “Static”)

CIM 2465 Intro to TCP/IP37 Learning by Routing Protocols Each router sends messages to the routers attached to the same subnets, which essentially list all the routing information each router knows. Thus all routers learns all the routes.

CIM 2465 Intro to TCP/IP38 RIP (Routing Information Protocol) R2 knows a connected route to , so RIP then advertises this route to R1

CIM 2465 Intro to TCP/IP39 Using Metrics to Pick the Best Routes Routing protocols must be able to choose between competing alternative routes

CIM 2465 Intro to TCP/IP40 Using Metrics to Pick the Best Routes By Metric, some kind of measurement Allows a router to measure how good each route is –Hop Count (RIP) –Bandwidth, Delay, Loading, Reliability (IGRP, EIGRP) –Cost (OSPF) –Clock Ticks (Novell IPX)

CIM 2465 Intro to TCP/IP41 Routing Protocol Metrics

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CIM 2465 Intro to TCP/IP44 Routing Protocol Algorithms Distance Vector Algorithms –“distance to neighboring routers” as the metric (e.g. Hop count in RIP) –No information about the topology of the network beyond the neighboring routers Link State Algorithms –Advertise information about the entire topology –Shortest Path Algorithm Hybrid Algorithms

CIM 2465 Intro to TCP/IP45 Classless Vs Classful Routing Protocols Variable-length Subnet Masking (VLSM) –Provides a great deal of flexibility when subnetting a single Class A, B, or C network –Different subnet masks can be used on different subnets of the same Class A, B, or C network –Allows network engineers to reduce the number of wasted IP addresses A Classful routing protocol does not send subnet masks in routing updates, so it cannot support VLSM A Classless routing protocol does send subnet masks in routing updates, so it does support VLSM

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