CSCI 465 D ata Communications and Networks Lecture 24 Martin van Bommel CSCI 465 Data Communications & Networks 1

Internet An interconnected set of networks where each of the constituent networks retains its identity and protocols Consists of – End systems devices attached to a network – Intermediate systems provide a communications path and perform the necessary relaying and routing functions bridges and routers CSCI 465 Data Communications & Networks 2

Bridge vs Router Bridge – intermediate system to connect two LANs that use similar LAN protocols – acts as address filter to transfer packets – operates at layer 2 - network access layer Router – intermediate system to connect two networks that may or may not be similar – operates at layer 3 - internet layer CSCI 465 Data Communications & Networks 3

TCP/IP Concepts 4

Internetworking Requirements Provide a link between networks – At minimum, physical and link control is needed Router J has physical links to N1&N2 - data link protocol Provide for the routing and delivery of data Application X on host A exchanges data with X on host B Provide an accounting service – Track of use and status of networks and routers Provide the services regardless of architectures CSCI 465 Data Communications & Networks 5

Network Differences addressing schemes (but global IP address) maximum packet size – break up for smaller network access mechanisms timeouts error recovery status reporting routing techniques user access control Connection vs connectionless CSCI 465 Data Communications & Networks 6

Connectionless Operation Internetworking is connectionless at IP level – Each network protocol data unit (PDU) is routed independently through series of routers Advantages – Flexible – requires very little from underlying nets – Robust – responds to changing conditions – Less overhead – no connection established CSCI 465 Data Communications & Networks 7

8 IP Operation

IPv4 – Internet Protocol Version 4 Part of the TCP/IP suite Two parts – Specification of interface with higher layer Interaction with e.g. TCP – Specification of actual protocol format and mechanisms CSCI 465 Data Communications & Networks 9

IP Services Service Primitives – send and deliver Parameters – Source and destination address – Protocol – e.g. TCP or UDP – Type of service indicators – Identification – used for reassembly – Don’t fragment identifier – Time to live (TTL) – in seconds – Data length – Option data – specify user options (next slide) – Data itself CSCI 465 Data Communications & Networks 10

IP Options Parameter Security Source routing – Sequence of router addresses Route recording – Sequence of routers visited Stream identification – Identify as stream to gain certain resources Timestamping CSCI 465 Data Communications & Networks 11

IPv4 Header CSCI 465 Data Communications & Networks 12

IPv4 address Formats CSCI 465 Data Communications & Networks 13

IP Addresses – Class A Start with binary 0 Range 0.x.x.x to 127.x.x.x – 0 is reserved – 127 used for loopback 126 Class A network numbers 2 24 = 16.7 million host numbers on each CSCI 465 Data Communications & Networks 14

IP Addresses – Class B Start with binary 10 Range 128.x.x.x to 191.x.x.x – Second octet also used as part of network number 2 14 = 16,384 Class B network numbers 2 16 = 65,536 host numbers on each CSCI 465 Data Communications & Networks 15

IP Addresses – Class C Start with binary 110 Range 192.x.x.x to 223.x.x.x – Second and third octets also used as part of network number 2 21 = 2,097,152 Class C network numbers 2 8 = 256 host numbers on each Network numbers nearly all allocated – IPv6 CSCI 465 Data Communications & Networks 16

Subnets and Subnet Mask Insulate overall internet from growth of network numbers and routing complexity – allows arbitrary complexity of internetworked LANs within organization – site looks to rest of internet like single network Assign single network number to all LANs – simplifies addressing and routing to the site Each LAN on the site assigned subnet number – host portion of IP address partitioned into subnet and host numbers Local routers route on basis of subnet number – Subnet mask used to convert IP address into subnet and host numbers CSCI 465 Data Communications & Networks 17

IP Addresses and Subnet Masks 18 Binary RepresentationDot Notation IP Address Subnet Mask Bitwise AND Subnet Number Host Number = 1305 MasksBinary RepresentationDot Notation Class A Default Class A Example Class B Default Class B Example Class C Default Class C Example