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© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

1

Nir Ingbar

Introduction to
Networking

(Routing & Switching)

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

2

Agenda


OSI 7 Layers model


Layer 1 & 2


Frame forwarding & filtering


VLAN, dot1Q Trunking


IP


Routing

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

3

OSI 7 Layers
model
(1977 by
ISO)

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

4

OSI Model Layer’s definitions


Each OSI layer performs unique and
specific task


A layer only has a knowledge of its
adjacent layers


A layer uses the services of a layer below


A layer performs functions and provides
service to the layer above


A layer service is independent of its
implementation

Application

Presentation

Session


Data Link

Physical

Transport

Network

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

5

OSI Model Layers


Physical
: Electrically encodes and physically
transfers messages between nodes


Data Link
: Provides reliable transit of data
across a physical link, handling physical
addressing, link discipline, error detection,
ordered delivery of frames and flow control


Network
: Provides connectivity and path
selection between two end systems that may
be located on geographically diverse sub
-
networks


Transport
: End
-

to
-

end control & information
exchange with a level of reliability required for
the applications

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

6

OSI Model Layers (cont.)


Session
: Manages the connection between
cooperating applications


Presentation
: Transforms data to and from
negotiated standardized formats


Application
: Provides the window between
the application process and OSI

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

7

Data encapsulation

Application

Presentation

Session


Data Link

Physical

Transport

Network

Application

Presentation

Session


Data Link

Physical

Transport

Network

Data

Data

Data Unit

Data Unit

SH

TH

Data Unit

NH

Data Unit

DLH

FCS

Bits

* FCS (Frame Check Sequence)

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

8

Internetworking Devices

Application

Presentation

Session


Data Link

Physical

Transport

Network

Application

Presentation

Session


Data Link

Physical

Transport

Network

Hub/Repeater

Switch/Bridge

Router

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

9

Protocol Suite

Application

Presentation

Session

Transport

Network

Data Link

Physical

Telnet

FTP

SMTP

TFTP

BOOTP

SNMP

TCP

UDP

IP

ICMP

ARP

Ethernet, Token Ring, FDDI,

WAN synchronous

© 2006 Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

10

Layer
1
&
2

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

11

Device Types


Hub
-

multi port repeater, provide connectivity,
allowing attached devices a path between which they
can communicate, works on layer one


Switch


connecting hosts


Bridge


connecting networks, can’t identify different
logical networks




©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

12

Bridge vs. Switch


Bridge usually have two interfaces and can connect to
physical networks


Switches usually have more than that


The main difference between a switch and bridge is the
number of networks each can connect


Switches are often aimed to connect workstations in a single
junction


Both are used inside LAN


Both operates on layers one and two


©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

13

Collision Domain


one of the logical network segments in which the data
packets can collide to each other


Collision domains are often referred as ‘Ethernet
segments'.


defined as a single CSMA/CD network segment in
which there will be a collision if two computers attached
to the system both transmit at the same time


A collision occurs when two or more network devices
are trying to transmit packets at the
exact same
time



©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

14

Collision domain
-

example

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

15

Collision domain
-

example

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

16

Type Of Transmission


Unicast

-

unicast transmission is the sending of
information packets to a single destination


Broadcast

-

broadcasting refers to transmitting a packet
that will be received (conceptually) by every device on the
broadcast domain


Multicast

-

multicast is a network addressing method for
the delivery of information to a group of destinations
simultaneously


Anycast



like multicast but only one address of a set of
addresses is chosen at any given time to receive
information from any given sender

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

17

MAC Address


48
bits (
6
octets) address space representing an unique
identifier to most network adapters or network interface
cards (NIC)


The first three octets identify the organization that
issued the identifier and are known as the
Organizationally Unique Identifier (OUI)


00
-
16
-
D
3
-
C
4
-
55
-
6
A

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

18

Broadcast Domain


represents the systems to which a given broadcast will
travel


broadcasts do not pass routers by default


If one station will broadcast, all the stations in this
domain will get the message


If a station wants to send a message out of the LAN, it
will have to know it’s Default Gateway

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

19

Broadcast domain


simple example

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

20

Collision domain
-

problem



©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

21


One switch can be a Single Point Of Failure


Adding an additional Switch can create broadcast storm.





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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

22


On running this algorithm the LAN is reduced to
an acyclic tree


The main idea of the Spanning Tree is for the
bridges to select the ports over which they will
forward frames


Solution: STP


Spanning tree
Protocol

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

23

Spanning Tree Protocol

With Spanning Tree

B
5

B
3

L
2

L
1

L
3

L
4

L
5

B
1

B
2

B
4

L
4

L
3

Actual Network

L
2

L
5

L
1

B
1

B
4

B
3

B
5

B
2

X

X

Spanning tree is designed to prevent loops in
bridged/switched Ethernet network based on the
root bridge concept, which is selected via
programmable parameters

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

24

Frame
forwarding &
filtering

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

25

Frame forwarding & filtering


The initial MAC address is empty

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

26

Frame forwarding & filtering (cont.)


Station A sends a frame to station C


The switch caches the MAC address of station A to port E
0
by
learning the source address of data frames


The frame from station A to station C is flooded out to all ports
except port E
0

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

27

Frame forwarding & filtering (cont.)


Station D sends a frame to station C


The switch caches the MAC address of station D to port E
3
by
learning the source address of data frames


The frame from station D to station C is flooded out to all ports
except port E
3

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

28

Frame forwarding & filtering (cont.)


Station A sends a frame to station C


The destination is known; the frame is not flooded

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

29

VLAN, dot
1
Q
Trunking

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

30

VLAN, dot
1
Q Trunking

802.1
Q Frame


FCS (Frame Check Sequence) is recalculated

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

31

Importance of native VLANs


VLAN
1
untagged traffic (native VLAN)


An
802.1
Q trunk and its associated trunk ports have a native
VLAN value.
802.1
Q does not tag frames for native VLAN.
Therefore, ordinary stations will be able to read the native
untagged frames, but will not be able to read any other frame
because the frames are tagged

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

32

IP

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

33

Internet Protocol
-

IP


Network Layer


Provides network layer services to TCP/IP
protocol suite


Responsible for forwarding packets
through network based on IP addresses



Best effort” delivery


Connectionless


Unacknowledged


Relies on a transport protocol to
guaranty delivery

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

34

IPv
4
Addressing


Address format: XXX.XXX.XXX.XXX
(
0

XXX

255
)


Addresses are
32
bits long
(
4
,
294
,
967
,
296
IP addresses)


Internet Assigned Numbers Authority
(IANA) assigns IP addresses for the
Internet


Divided into five classes three of which
are available to end
-
user networks


Consists Network and Host identification
fields

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

35

Available IP Addresses


Class D is reserved for multicast groups


Class E is reserved for future use

Class

Assigned Network/

/Host ID

Range of Network IDs

Max. Hosts

Per Network

A /8

NET.X.X.X

1

126

16,777,214

B /16

NET.NET.X.X

128.1


191.254

65,534

C /24

NET.NET.NET.X

192.0.1


223.255.254

254

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

36

Private Networks

Class

Assigned Network/

/Host ID

Range of Network IDs

A

NET.X.X.X

10.0.0.0
-

10.255.255.255

B

NET.NET.X.X

172.16.0.0
-

172.31.255.255

C

NET.NET.NET.X

192.168.0.0
-

192.168.255.255



RFC
1918

addresses

Not routed by Internet routers (filtered by Edge Routers)






RFC
2026

Link Local Addresses

169.254.0.1

169.254.255.255


Auto
-
assigned IP address to local host if DHCP server
cannot be contacted

Not routed by any router


©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

37

Other Reserved Addresses


127.0.0.1

127.255.255.255

Reserved for testing and loopback routines for IP Applications

ping
127.0.0.1

verifies the local host has properly loaded the
IP protocol


224.0.0.1

224.0.0.255

Class D multicast (IANA)

Reserved for well known services and network

topology mechanisms

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

38

Subnetting IP/VLSM/Classless


Allows to divide a single IP network into smaller
divisions


Subnets


Done by borrowing bits from the host portion of the
address


Subnet bits are defined by the Subnet Mask

IP Address

134.125.172.17

1

0

0

0

0

1

1

0

0

1

1

1

1

1

0

1

1

0

1

0

1

1

0

0

0

0

0

1

0

0

0

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

Subnet Mask

255.255.240.0

Or /
20

Subnet Host

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

39

Routing

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

40

Routing

Routing

is the act of moving information across an internetwork
from a source to a destination. Along the way, at least one
intermediate node typically is encountered. Routing is often
contrasted with bridging, which might seem to accomplish
precisely the same thing to the casual observer. The primary
difference between the two is that bridging occurs at Layer
2
(the
link layer) of the OSI reference model, whereas routing occurs at
Layer
3
(the network layer). This distinction provides routing and
bridging with different information to use in the process of moving
information from source to destination, so the two functions
accomplish their tasks in different ways.


The topic of routing has been covered in computer science
literature for more than two decades, but routing achieved
commercial popularity as late as the mid
-
1980
s. The primary
reason for this time lag is that networks in the
1970
s were simple,
homogeneous environments. Only relatively recently has large
-
scale internetworking become popular.

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

41

Routing


Static/Dynamic


IGP (Interior Gateway Protocol)


RIP,
ISIS, OSPF, (E)IGRP


EGP (Exterior Gateway Protocol)
-

BGP

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

42

Routing


Distance Vector


RIP, IGRP


Link State


OSPF, ISIS


Balanced hybrid
-

EIGRP

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2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

43

Distance


Vector Algorithm

A

C

B

D

Sends A’s
Routing Table

Computes B’s
Routing Table

Sends B’s
Routing
Table

Computes C’s
Routing Table

Computes D’s
Routing Table

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

44

Link
-

State Algorithm

A

C

B

D

Sends C’s Info on
Links to all
neighbors

Sends A’s,B’s, C’s
and D’s Info on
Links to all
neighbors

Sends D’s Info on
Links to all
neighbors


All routers calculate “shortest paths” using Djikstra algorithm

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

45

Routing

Route Source

Default Distance

Connected

0

Static

1

eBGP

20

EIGRP

90

IGRP

100

OSPF

110

ISIS

115

RIP

120

iBGP

200

Unknown*

255

* If the administrative distance is
255
, the router does not believe the
source of that route and does not install the route in the routing table

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

46

Q & A

©
2006
Cisco Systems, Inc. All rights reserved.

Cisco Confidential

Presentation_ID

47