Chapter 5 Network and Transport Layers Chapter 5

Chapter 5 Network and Transport Layers

Chapter 5 Outline Transport & Network Layer Protocols § TCP/IP Transport Layer Functions § Linking to the Application Layer § Segmenting § Session management Addressing § Assigning addresses and address resolution Routing § Types of routing, routing protocols, and multicasting TCP/IP Examples Copyright 2010 John Wiley & Sons, Inc

Network Layer Computer 1 Computer 2

5. 4 Routing Process of identifying what path to have a packet take through a network from sender to receiver Routing Tables § Used to make routing decisions § Shows which path to send packets on given destination § Kept by computers making routing decisions Dest. Next B B C B D D E D F D G B to reach a Routers § Special purpose devices used to handle routing decisions on the Internet § Maintain their own routing tables 5 -4

5. 4. 1 Simple Routing Example Possible paths from A to G: • ABCG • ABEFCG • ADEBCG A Routing Table for A Dest. Next B C D E F G Each node has its own routing table 5 -5

5. 4. 1 Routing Example – LAN with Routers 5 -6

5. 4 Routing 5 -7

5. 5. 1 TCP/IP Network Example 5 -8

5. 4. 1 Types of Routing Centralized routing § § Decentralized routing § § § 5 -9

5. 4. 2 Routing Protocols – how tables are set up Static routing: § Uses fixed routing tables developed by network managers • Each node has its own routing table • Changes when computers added or removed Dynamic routing or Adaptive routing: § Uses routing tables at each node that are updated dynamically § Based on routing condition information exchanged between routing devices § Types 5 - 10

5. 4. 2 Dynamic Routing Algorithms Distance Vector § Uses the least number of hops to decide how to route a packet Link State § Uses a variety of information types to decide how to route a packet (more sophisticated) • e. g. , number of hops, congestion, speed of circuit § Links state info exchanged periodically by each node to keep every node in the network up to date § Provides more reliable, up to date paths to destinations 5 - 11

5. 4. 2. 1 Routing Information Protocol (RIP) A dynamic distance vector interior routing protocol Operations: § Manager builds a routing table by using RIP § Routing tables broadcast periodically (every minute or so) by all nodes § When a new node added, RIP counts number of hops between computers and updates routing tables 5 - 12

5. 4. 2. 1 Open Shortest Path First (OSPF) A dynamic link state interior routing protocol Became more popular on Internet § More reliable paths § Less burdensome to the network 5 - 13

5. 5. 1 Sending Messages using TCP/IP Required Network layer addressing information 1. 2. 3. 4. Address information is obtained from a configuration file or provided by a DHCP server What additional information is needed for servers? 5 - 14

5. 5. 1 TCP/IP Configuration Information 5 - 15

5. 5. 1 Subnet Masks Tells the computer what part of an Internet Protocol address to be used to determine whether the destination is on the same subnet or on a different subnet Example § Subnet: 149. 61. 10. x § Subnet mask: 255. 000 Example § Subnets: 149. 61. 10. 1 -128, § Subnet mask 255. 128 5 - 16

5. 5. 1 TCP/IP Network Example 5 - 17

5. 5. 1 Moving Messages - TCP/IP and Layers How layers are handled in a LAN: • Host Computers • Packets move through all layers § Gateways, Routers • Packet moves from Physical layer to Data Link Layer through the network Layer At each stop along the way (e. g. from router to router): § Ethernet packets is removed and a new one is created for the next node § IP and above packets never change in transit (created by the original sender and destroyed by the final receiver) 5 - 18

5. 5. 1 Message Moving Through Layers 5 - 19

5. 5. 2 Known IP Address Transmit from A => E (A knows E’s IP Address) How many Hops will it take? PATH IP Source IP Destination Ethernet Source Ethernet Destination 5 - 20

5. 5. 3 Unknown IP Address Transmit from A => E (A doesn’t know E’s IP address) How do we do this? PATH IP Source IP Destination Ethernet Source Ethernet Destination DNS Request DNS Response 5 - 21

5. 5. 4 Unknown Data Link Address Transmit from A => E (doesn’t know E’s Ethernet address) • An ARP request from D will occur once the message sent by A is received by D. PATH IP Source IP Destination Ethernet Source Ethernet Destination 5 - 22

5. 5. 2 Known IP Address and Ethernet Address Transmit from B => F (B knows F’s IP Address) PATH IP Source IP Destination Ethernet Source Ethernet Destination 5 - 23

5. 5. 3 Unknown IP Address Transmit from B => F (B doesn’t know F’s IP address) PATH IP Source IP Destination Ethernet Source Ethernet Destination 5 - 24

5. 5. 4 Unknown Ethernet Address Transmit from B => F (doesn’t know F’s Ethernet address) PATH IP Source IP Destination Ethernet Source Ethernet Destination 5 - 25

Implications for Management Most organizations moving toward a single standard based on TCP/IP § Decreased cost of buying and maintaining network equipment § Decreased cost of training networking staff Telephone companies with non-TCP/IP networks are also moving toward TCP/IP § Significant financial implications for telcos § Significant financial implications for networking equipment manufacturers 5 - 26