Internetworking and Network Layer in Internet

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Oct 29, 2013 (3 years and 8 months ago)

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Internetworking and Network Layer
in Internet





Lecture
-
33
-
35

1.
Tunneling, Internetwork Routing

2.
Fragmentation

3.
IP
-
Protocol

4.
IP
-
Address Classes(A,B,C,D,E), Broadcast address , Multicast address, Network Mask,
Subnetting

5.
Internet control Protocol
-
ICMP,IGMP

6.
OSPF
-
Interior Gateway Routing Protocol

7.
BGP
-
Exterior Gateway Routing Protocol

8.
Internet Multicasting

9.
Mobile
-
IP

10.
IPv6

Tunneling…..









Internetworking two different networks is
difficult


Connecting Networks

How Networks Differ

Some of the many ways networks can differ.

Tunneling a packet from Paris to
London.


Problem: Here source and destination are on same type of network but there is
different kind of network in between.


Solution: Tunneling




Internetwork Routing

(a)
An
internetwork
.
(b)

A graph of the






internetwork.











Once the graph has been constructed, Distance Vector and Link state
routing can be applied to set of multiprotocol routers. This gives a two
level routing algorithm:

1.
Within each network an
interior gateway protocol
is used

2.
But between networks, an
exterior gateway protocol
is used




Internetwork routing



Requires crossing
international boundaries


1.
Various laws come in to
play like :
sweden’s

privacy
law about exporting
personal data about
swedish

citizen from
sweden

2.
Canadian law saying data
originated from can add
and destined in
canada

may not leave the country.

Internetwork routing


COST: within a network
only one algorithm applies
but different networks may
be under different
managements , so there
will be different routes with
different cost and quality of
service


Within a big internetwork it
is difficult to choose best
route as it is time
consuming.

Fragmentation


Network designers are not free to chose any maximum packet
size they wish.( hardware, od, protocols, error handling)


Problem: when a large packet wants
to
travel
through a
network
whose max packet size is too small.

1.
Solution 1: use routing algorithm that avoid sending packets
to route that support small packet size.

2.
Fragmentation: divide the big packet into small


But reverse process is not easy. ( 2
nd

law of
thermodynamic)


There are two schemes to combine the packets again:

a)
Transparent

b)
Non
-

transparent




Fragmentation

(a)

Transparent fragmentation.
(b)

Nontransparent fragmentation.

Fragmentation (2)

Fragmentation when the elementary data size is 1 byte.

(a)

Original packet, containing 10 data bytes.

(b)

Fragments after passing through a network with
maximum packet size of 8 payload bytes plus header.

(c)

Fragments after passing through a size 5 gateway.


The Network Layer in the Internet


The IP Protocol


IP Addresses


Internet Control Protocols


OSPF


The Interior Gateway Routing Protocol


BGP


The Exterior Gateway Routing Protocol


Internet Multicasting


Mobile IP


IPv6

Design Principles for Internet

1.
Make sure it works.

2.
Keep it simple.

3.
Make clear choices.

4.
Exploit modularity.

5.
Expect heterogeneity.

6.
Avoid static options and parameters.

7.
Look for a good design; it need not be perfect.

8.
Be strict when sending and tolerant when receiving.

9.
Think about scalability.

10.
Consider performance and cost.

Collection of Subnetworks

The Internet is an interconnected collection of many
networks.


IP


The

IP

is

the

internetworking

protocol

that

offers

a

service

with

the

following

characteristics
:



It

is

connectionless,

so

units

of

network

layer

data

protocol

,denominated

datagram

in

the

IP

context,

are

dealt

with

in

an

individual

way

from

the

source

host

up

to

the

destination

host


It

is

not

reliable
.

The

data
-
grams

can

be

lost,

duplicated,

or

disordered,

and

the

network

does

not

detect

or

report

this

problem



Part of TCP/IP


Used by the Internet


Specifies interface with higher layer


e.g. TCP


Specifies protocol format and mechanisms


IPv4


addresses are 32 bits wide


Its header is 20 bytes at minimum


Uses doted
-
decimal notation (e.g. 43.23.43.56)


IPv6


Provides larges address domain; addresses are 128 bits wide


Multiple separate headers are supported


Handles audio and video; providing high quality paths


Supports
unicast
, multicast,
anycast




The IP
Protocol


IP packets all have a
header

as shown


IP Header format


The version field

keeps track of which version of the protocol
the datagram belongs to.



Hlen

is provided to tell how long the header is in 32
-
bit words


The type of service field

allows the host to tell the subnet
what kind of service it wants. Various combinations of
reliability and speed are possible. The three flag bits allow the
host to specify what it cares most about from the net [delay,
throughput, reliability]


The total length

includes everything in the datagram


both
header and data

IP Header Format


The identification field

is needed to allow the destination
host to determine which datagram a newly arrived fragment
belongs to. All the fragments of a datagram contain the same
identification value


DF = Don’t Fragment


MF = More Fragment



The fragment offset

tells where in the current datagram this
fragment belongs



The time to live field

is a counter used to limit packet
lifetimes



The protocol field
tells it which transport process to give it to,
TCP, UDP and some others




IP Header Format


The header checksum verifies the header only. Checksum is useful to
detecting errors generated by bad memory words inside a router


The source address and destination address indicate the network number and
host numbers


The option field was designed to provide an escape to allow subsequent
version of the protocol to include information not present in the original
design

Option

Description

Security

Strict source routing

Loose source routing

Record route

Timestamp

Specifies how secret the datagram is

Gives the complete path to be followed

Gives a list of routers not to be missed

Makes each router append its IP address

Makes each router append its address and timestamp

Internet Control Protocols


IP protocol only deal with the data transfer


We need control protocol to check the
network


ICMP, ARP, RARP, BOOTP, HDCP



Internet Control Message

Protocol (ICMP)


ICMP error messages are used by
routers
and
hosts

to tell a device that
sent a datagram about problems encountered in delivering it


Used to test the network


Messages are encapsulated in the IP packet


Has many message types


ARP (address resolution protocol)


Exploits broadcast property of a LAN


Each host on LAN maintains a a table of IP
subnetwork addresses


If the address can not be found ARP
broadcasts a request


Shouting:

Who know about this IP address?


Other hosts listen and reply


The reply includes IP address and MAC


Any interested host can learn about the new
information


ARP Example


Assume 1 is sending a message to
2

(
rose@sonoma.edu
)



Sonoma.edu is the host


Host
1 sends a message to Domain Name System (DNS): what is the IP address for
Sonoma.edu?


192.31.65.5


What is the MAC address for 192.31.65.5? Use ARP broadcast!


Host 2 respond: it is E2


Host 1 maps IP and MAC; encapsulate the IP message in the Ethernet frame and send it


Cashing can enhance ARP operation




ARP Example


Assume 1 is sending a message to
4

(
rose@sonoma.edu
)



Sonoma.edu is the host


Host
1 sends a message to Domain Name System (DNS): what is the IP address for
Sonoma.edu?


192.31.65.8
What is the MAC address for
192.31.65.8?
ARP cannot pass through the router!



Two choices:


Reconfigure routers to response to ARP (Proxy ARP)


Send the message to the LAN router (E3)

F1

F3

4


Each router looks are the IP address and passes it to
the next node using the routing table




Reverse Address Resolution Protocol
(RARP)


Allows a station to determine its IP address from
its hardware address


A server can be configured to respond to RARP
request automatically allocating IP address across
the network


Not used much nowadays, replaced instead by
more powerful auto configuration protocols such
as DHCP (Dynamic Host Configuration Protocol)

A. S. TanenBaum, "Computer
Networks," Pearson Education,
2003, pp. 453
-
454.

[1]

Remember…


This is My MAC; what is my IP address?
RARP




This
is the destination host name, what it is IP
address?
DNS Server



This
is the IP address, what is your` MAC
address?
ARP

IP Addresses

IP address formats.

IP Addresses (2)

Special IP addresses.