Networks I

Internet Protocol

Instituto Tecnológico y de Estudios Superiores de Monterrey Campus Estado de México

Prof. MSc. Ivan A. Escobar Broitman

TC1007

Introduction

“Many networks exist in the world, often with different hardware and software. People connected to one network want to communicate with people attached to a different one. This desire requires connecting together different, and frequently incompatible networks, sometimes by using machines called gateways to make the connection and provide the necessary translation, both in the terms of hardware and software. A collection of interconnected networks is called an inter-network or just Internet”

___________

Tananebaum pg16.

Network ArquitectureHow are networks interconnected?

Red 1 GW Red 2

Red 1 GW1 Red 2 GW2 Red3

Network ArquitectureInternet Protocol:

It is the glue that holds together the Internet. It treats all the networks in the same way, for

example a LAN like Ethernet or Token Ring, a Wan like ARPANET and even a point to point link between two computers.

Designed with internetworking in mind.

Network Arquitecture: IP

IP in the OSI MODEL

Aplications

Trustworthy Transport Service

Best Effort no Connection Transfer of Packets

L7

L4 TCP

L3 IP

Ethernet Frames: Data Link Layer

a) DIX Ethernet Frame b)IEEE 802.3 Frame

Frame Demultiplexing in Ethernet

IP ModuleARP Mod. RARP Mod.

Demux Based on Frame Type

Frame Arrival

0X800 0X8350X806

The Internet Protocol (IP)

Provides mechanisms to transport units called IP datagrams.

IP is a “best effort” protocol.

Delivery of datagrams is not guaranteed by this protocol.

IP is made up of 5 parts: Datagram Format. Datagram Routing. Error Control. Fragmentation IP Options.

DATAIP HEADER

The fundamental part of the internet services are the delivery of packets.

IP Frame Format

0 4 8 16 19 24 31

IPv4 Frame Fields Version (4 bits):

Version of the protocol, currently IPv4.

Assures compatibility during transition.

IHL (4 bits): Tells us how long is the

header. Default Value = 5, no

options, header 20 bytes. Max value is 15 which

limits header to 60 bytes.

Type of Service (8 bits): Specifies the way to

process a datagram.

Precedence UnusedRTD

– Precedence: priority from 0 (normal) to 7.

– Three flag bits allow the hosts to specify what they care most about the set (Delay, Throughput, Reliability)

IPv4 Frame Fields Total Length (16 bits):

Includes the length of data and header.

Maximum theoretical length 64Kbytes.

Identification (16 bits): Frame identification.

Unused bit.

DF (1 bit): Don’t Fragment. Avoid small packet

networks.

MF (1 bit): More fragments. Used to acknowledge

when the last fragment has arrived.

All fragments except the last one have it set.

Fragment Offset (13 bits): Tells us where in the

current datagram the fragment is.

Maximum fragments per datagram > 8192.

IPv4 Frame FieldsTime To live (TTL 8

bits): Theoretically marks the

maximum lifetime in seconds of a packet. In practice it counts hops.

Initialised to 255, decremented by one at each hop.

Prevents packets from wondering around the net forever.

Protocol (8 bits): Tells us which protocol to

use to interpret the information in the data area. (TCP,ARP,etc.)

Analogous to the Type Field in Ethernet.

Header Checksum

(16 bits): Used to verify the header

of a packet.

Source and Destination Address (32 bits): Indicate network and host

numbers.

Analogy between Type and Protocol

When Protocol field is initialized to:1 it indicates that in the datagram area we have

encapsulated the ICMP protocol17 it indicates that in the datagram area we have

encapsulated the UPD protocol6 it indicates that in the datagram area we have

encapsulated the TCP protocol

Frame Encapsulation

Datagram

Header Data

DataHeader

Frame

IPv4 Frame FieldsOptions Field (0 40 bytes):

Used to include information not present in the original design.

Information for network test.Rarely used. Variable in length.

IPv4 Frame Fields

Some of the IP Options

IPv4 Frame Fields: Options Security:

How secret the information might be.

Military applications. Monitor specific data.

Strict Source Routing: Establishes complete

path to follow from source to destination.

Useful for emergency packets.

Loose Source Routing: Specifies certain

routers the packet must travel from source to destination.

Allows packets to choose other routers on the way.

Application, send routers through a certain type of route.

IPv4 Frame Fields: OptionsRecord route:

Each router along the path from source to destination writes down its IP address in the options field.

Managers can track down bugs in routing algorithm.

Used to debug and to modify existing routing algorithms.

Ex: packet from ITESM to UNAM.

Timestamp: Similar to record route

option. Routers record both a

32 bit IP address and a 32 bit timestamp.

Used mainly for debugging and algorithm creation.

Are 40 bytes enough?

IP: Options.

Options are included to:Test and Depure the network.

IP OPTIONS FIELD :0 8 16 24 31

0 1 2 3 4 5 6 7

CODE LENGTH POINTER PADDING

COPY OPTION CLASS OPTION NUMBER

IP Options

Class Num Op Long Description

0 3 var Loose source routing

0 7 var Record route

0 9 var Strict source routing

2 4 var Internet timestamp

IP AddressesIP address formats.

IP AddressesNIC:

Network Information Center.Assigns only netid portion of the IP address.Host id is the responsibility of the Network

Administrator.Examples:

Lans.Websites.

IP Addresses Special IP addresses.