S305 – Network Infrastructure 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 1Computer 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 to reach a given destination  Kept by computers making routing decisions Routers  Special purpose devices used to handle routing decisions on the Internet  Maintain their own routing tables Dest. B C D E F G Next B D B

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

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

5.4.2 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

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

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

5.5.1 Sending Messages using TCP/IP Required Network layer addressing information Address information is obtained from a configuration file or provided by a DHCP server What additional information is needed for servers?

TCP/IP Configuration Information

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: x  Subnet mask: Example  Subnets: ,  Subnet mask

5.5.1 TCP/IP Network Example

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)

5.5.1 Message Moving Through Layers

5.5.2 Known IP Address Transmit from A => E (A knows E’s IP Address) How many Hops will it take? PATHIP Source IP Destination Ethernet Source Ethernet Destination

5.5.3 Unknown IP Address Transmit from A => E (A doesn’t know E’s IP address) How do we do this? PATHIP Source IP Destination Ethernet Source Ethernet Destination DNS Request PATHIP Source IP Destination Ethernet Source Ethernet Destination DNS Response

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 PATHIP Source IP Destination Ethernet Source Ethernet Destination

Known IP Address and Ethernet Address Transmit from B => F (B knows F’s IP Address) PATHIP Source IP Destination Ethernet Source Ethernet Destination

Unknown IP Address Transmit from B => F (B doesn’t know F’s IP address) PATHIP Source IP Destination Ethernet Source Ethernet Destination

Unknown Ethernet Address Transmit from B => F (doesn’t know F’s Ethernet address) PATHIP Source IP Destination Ethernet Source Ethernet Destination

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