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Transcript of Networks I Internet Protocol Instituto Tecnológico y de Estudios Superiores de Monterrey Campus...
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.