Chapter 5 Network and Transport Layers Part 2

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 Layers Computer 1 Computer 2

Network Layer Functions Addressing Each device on the path between source and destination must have an address Internet Addresses Assignment of addresses Translation between network layer addresses and other addresses (address resolution) Routing Process of deciding what path a packet must take to reach destination Routing protocols Transport Layer Network Layer Data Link Layer

5.3.2 Dynamic Addressing Giving addresses to clients (automatically) only when they are logged in to a network Uses a server to supply IP addresses to computers whenever the computers connect to network

5.3.2 Programs for Dynamic Addressing Protocols: Bootstrap Protocol (bootp) Dynamic Host Control Protocol (DHCP) Different approaches, but same basic operations:

5.3.3 Address Resolution Server Name Resolution Data Link Layer Address Resolution

5.3.3 Server Name Resolution - DNS Used to determine IP address for a given URL Provided through a group of name servers Databases containing directories of domain names and their corresponding IP addresses Large organizations maintain their own name servers smaller organizations rely on name servers provided by their ISPs When a domain name is registered, IP address of the DNS server must be provided to registrar for all URLs in this domain Example: Domain name: uncw.edu URLs: www.uncw.edu, csb.uncw.edu, www.uncw.edu/cas/index.html

5.3.3 How DNS Works – Directory Service Where are address tables located?

5.3.3 How DNS Works (Cont.) If the URL is NOT in the local DNS server Sends DNS request packet to the next highest name server in the DNS hierarchy Usually the DNS server at the top level domain (such as the DNS server for all .edu domains) If the URL is NOT in the name server Sends DNS request packet ahead to name server at the next lower level of the DNS hierarchy

5.3.3 DNS Hierarchy

5.3.3 DNS Hierarchy http://www.root-servers.org/

5.3.3 How DNS Works – Internal Request

5.3.3 How DNS Works – External Request

5.3.4 MAC Address Resolution Problem: Unknown MAC address of the next node (whose IP address is known) Solution: Operation:

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

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

5.4.1 Routing Example – LAN with Routers

5.4 Routing

5.5.1 TCP/IP Network Example

5.4.1 Types of Routing Centralized routing Decentralized routing

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

5.5.1 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?

5.5.1 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: 149.61.10.x Subnet mask: 255.255.255.000 Subnets: 149.61.10.1-128, Subnet mask 255.255.255.128

5.5.1 TCP/IP Network Example

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)

5.5.1 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? PATH IP Source Destination Ethernet

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 Destination Ethernet DNS Request PATH IP Source Destination Ethernet 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. PATH IP Source Destination Ethernet

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

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

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