Internetworking Technologies EA C451/MBA C451

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Oct 23, 2013 (3 years and 5 months ago)

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Internetworking Technologies

EA C451/MBA C451




Ethernet Technology


Ethernet

is

the

name

given

to

a

popular

packet
-
switched

LAN

technology

invented

at

Xerox

PARC

in

the

early

1970
s


Using

Ethernet,

data

can

be

transmitted

at

10

Mbps
.


Ethernet

versions


l
0
OBase
-
T,

or

Fast

Ethernet
:

100

Mbps


dual
-
speed

Ethernet

or

I
0
/
100

Ethernet
:



1000

Base
-
T,

or

giga

bit

Ethernet
:

1

Gbps



MAC Address


A

Media

Access

Control

address

(
MAC

address
)

is

a

unique

identifier

assigned

to

network

interfaces

for

communications

on

the

physical

network

segment
.


MAC

addresses

are

used

for

numerous

network

technologies

and

most

IEEE

802

network

technologies

including

Ethernet
.

Logically,

MAC

addresses

are

used

in

the

Media

Access

Control

protocol

sub
-
layer

of

the

OSI

reference

model
.


MAC

addresses

are

most

often

assigned

by

the

manufacturer

of

a

network

interface

card

(NIC)

and

are

stored

in

its

hardware,

the

card's

read
-
only

memory,

or

some

other

firmware

mechanism
.



It

may

also

be

known

as

an

Ethernet

hardware

address
(
EHA
),

hardware

address

or

physical

address
.



MAC Address


The

standard

(IEEE

802
)

format

for

printing

MAC
-
48

addresses

in

human
-
friendly

form

is

six

groups

of

two

hexadecimal

digits,

separated

by

hyphens

(
-
)

or

colons

(
:
),

in

transmission

order,

e
.
g
.

01
-
23
-
45
-
67
-
89
-
ab,

01
:
23
:
45
:
67
:
89
:
ab
.



This

form

is

also

commonly

used

for

EUI
-
64
.



Another

convention

commonly

used

by

networking

equipment

uses

three

groups

of

four

hexadecimal

digits

separated

by

dots

(
.
),

e
.
g
.

0123
.
4567
.
89
ab
;

again

in

transmission

order
.


This

48
-
bit

address

space

contains

potentially

2
48

or

281
,
474
,
976
,
710
,
656

possible

MAC

addresses
.


The

IEEE

expects

the

MAC
-
48

space

to

be

exhausted

no

sooner

than

the

year

2100
;

EUI
-
64
s

are

not

expected

to

run

out

in

the

foreseeable

future
.



MAC Address

The following technologies use the MAC
-
48 identifier format:


Ethernet


802.11

wireless networks


Bluetooth


IEEE 802.5

token ring


most other IEEE 802 networks


FDDI


ATM

(switched virtual connections only, as part of an

NSAP
address)


Fibre Channel

and

Serial Attached SCSI

(as part of a

World
Wide Name)




MAC Address
-

Usage


Although

intended

to

be

a

permanent

and

globally

unique

identification,

it

is

possible

to

change

the

MAC

address

on

most

of

today's

hardware,

an

action

often

referred

to

as

MAC

spoofing
.


A

host

cannot

determine

from

the

MAC

address

of

another

host

whether

that

host

is

on

the

same

link

(network

segment)

as

the

sending

host,

or

on

a

network

segment

bridged

to

that

network

segment
.


In

TCP/IP

networks,

the

MAC

address

of

an

interface

can

be

queried

knowing

the

IP

address

using

the

Address

Resolution

Protocol

(ARP)

for

Internet

Protocol

Version

4

(IPv
4
)

or

the

Neighbor

Discovery

Protocol

(NDP)

for

IPv
6
.



On

broadcast

networks,

such

as

Ethernet,

the

MAC

address

uniquely

identifies

each

node

on

that

segment

and

allows

frames

to

be

marked

for

specific

hosts
.



It

thus

forms

the

basis

of

most

of

the

Link

layer

(OSI

Layer

2
)

networking

upon

which

upper

layer

protocols

rely

to

produce

complex,

functioning

networks
.





Ethernet

was

designed

to

be

a



shared

bus
:

because

all

stations

connect

to

a

single,

shared

communication

channel
.


broadcast

technology

because

all

stations

receive

every

transmission,

making

it

possible

to

transmit

a

packet

to

all

stations

at

the

same

time
.



best
-
effort

delivery

mechanism

because

the

hardware

provides

no

information

to

the

sender

about

whether

the

packet

was

delivered
.


Access

control

is

distributed

because

Ethernet

has

no

central

authority

to

grant

access
.

The

Ethernet

access

scheme

is

called

Carrier

Sense

Multiple

Access

with

Collision

Detect

(CSMA/CD)
.




Ethernet Packet Format



Address Resolution Protocol


At

nearly

every

layer

of

a

network

architecture

there

are

several

potential

protocols

that

could

be

used
.

For

example,

at

a

high

level,

there

is

TELNET

and

SUPDUP

for

remote

login
.


Somewhere

below

that

there

is

a

reliable

byte

stream

protocol,

which

might

be

CHAOS

protocol,

DOD

TCP,

Xerox

BSP

or

DECnet
.


The

10
Mbit

Ethernet

allows

all

of

these

protocols

(and

more)

to

coexist

on

a

single

cable

by

means

of

a

type

field

in

the

Ethernet

packet

header
.


However,

the

10
Mbit

Ethernet

requires

48
.
bit

addresses

on

the

physical

cable,

yet

most

protocol

addresses

are

not

48
.
bits

long,

nor

do

they

necessarily

have

any

relationship

to

the

48
.
bit

Ethernet

address

of

the

hardware
.


For

example,

CHAOS

addresses

are

16
.
bits,

DOD

Internet

addresses

are

32
.
bits,

and

Xerox

PUP

addresses

are

8
.
bits
.




Address Resolution Protocol


A

protocol

is

needed

to

dynamically

distribute

the

correspondences

between

a

<protocol,

address>

pair

and

a

48
.
bit

Ethernet

address
.

ARP

is

the

solution
.


The

Address

Resolution

Protocol

(
ARP
)

is

a

computer

networking

protocol

for

determining

a

network

host's

Link

Layer

or

hardware

address

when

only

its

Internet

Layer

(IP)

or

Network

Layer

address

is

known
.


This

function

is

critical

in

local

area

networking

as

well

as

for

routing

internetworking

traffic

across

gateways

(routers)

based

on

IP

addresses

when

the

next
-
hop

router

must

be

determined
.



ARP

was

defined

by

RFC

826

in

1982


ARP

has

been

implemented

in

many

types

of

networks,

such

as

Internet

Protocol

(IP),

CHAOS,

DECNET,

Xerox

PARC

Universal

Packet,

Token

Ring,

FDDI,

IEEE

802
.
11

and

other

LAN

technologies,

as

well

as

the

modern

high

capacity

networks,

such

as

Asynchronous

Transfer

Mode

(ATM)
.


In

the

next

generation

Internet

Protocol,

IPv
6
,

ARP's

functionality

is

provided

by

the

Neighbor

Discovery

Protocol

(NDP)
.





Address Resolution Protocol


To discover the Ethernet MAC address:





Before

sending

an

IPv
4

packet,

the

sender

sends

a

broadcast

message

onto

the

LAN

using

ARP

in

order

to

discover

the

Ethernet

MAC

address

of

an

interface

that

is

listening

for

that

desired

target

IPv
4

address
.

If

operational,

an

appropriate

unit

will

reply

that

it

has

a

network

interface

with

a

certain

MAC

address

that

is

associated

with

the

IPv
4

address

in

question
.

The

original

sender

now

has

the

information

needed

and

can

send

its

IPv
4

packet

to

the

destination,

inserting

it

into

an

Ethernet

frame

with

the

correct

destination

MAC

address

for

the

appropriate

recipient
.



ARP: Packet Structure



ARP: Packet Structure




ARP: Packet Description


Hardware type (HTYPE): This field specifies the Link Layer
protocol type. Example: Ethernet is 1.


Protocol type (PTYPE): This field specifies the upper layer
protocol for which the ARP request is intended. For IPv4, this
has the value 0x0800.


Hardware length (HLEN): Length (in

octets) of a hardware
address. Ethernet addresses size is 6.


Protocol length (PLEN): Length (in octets) of addresses used
in the upper layer protocol. (The upper layer protocol specified
in PTYPE.) IPv4 address size is 4.


Operation:

Specifies the operation that the sender is
performing: 1 for request, 2 for reply.



ARP: Packet Description


Sender

hardware

address

(SHA)
:

Hardware

(MAC)

address

of

the

sender
.


Sender

protocol

address

(SPA)
:

Upper

layer

protocol

address

of

the

sender
.


Target

hardware

address

(THA)
:

Hardware

address

of

the

intended

receiver
.

This

field

is

ignored

in

requests
.


Target

protocol

address

(TPA)Upper

layer

protocol

address

of

the

intended

receiver
.


ARP Probe



An

ARP probe

is an ARP request constructed with an all
-
zero

sender IP address
. The term is used in the

IPv4 Address
Conflict Detection
specification (RFC 5227).


Before

beginning

to

use

an

IPv
4

address

(whether

received

from

manual

configuration,

DHCP,

or

some

other

means),

a

host

implementing

this

specification

must

test

to

see

if

the

address

is

already

in

use,

by

broadcasting

ARP

probe

packets
.