LOKALNE SIECI

KOMPUTEROWE

 Współpraca sieci LAN - urządzenia pośredniczące.
Rola routerów i przełączników.
 Sieci typu VLAN.

MD – Mediation Devices or Connecting Devices
(repeater, bridge, …)

heterogeneous MD

Token Ring

Ethernet

Ethernet

homogeneous MD

MD

MD

LAN interconnection

LAN interconnection by analog telephone lines

LAN 1

Modem

Modem

LAN 2

Analog

telephone line

NT 2

NT 1

LAN A

A 1

NT 1

NT 2

LAN B

A 1

LAN C

A 1

NT 2

NT 1

LAN D

A 1

NT 2

NT 1

ISDN

S

T

U

U

U

U

S

T

T

S

T

S

LAN interconnection by N-ISDN

LAN interconnection by B-ISDN (ATM)

N – ATM Node (switch)
NT1 – Network
Termination

LAN A

N

N

N

N

NNI

NNI

NNI

NNI

NNI

NT1

NT1

NT1

NT1

UNI

UNI

UNI

UNI

LAN B

LAN C

LAN D

Connecting devices

Networking

Devices

Internetworking

Devices

Hub/Repeater

Bridge/

Switch L2

Router/

Switch L3

Gateway

Connection Devices

Router/Switch

•

Repeater is a low-level devices that amplify or regenerate

weak signals

• Repeater is used to join network segments together
to increase the total length of the network
• Act at the physical layer and allow all traffic to cross LAN

segments

What is a Repeater ?

Repeater

(HUB)

REPEATER

S

• Hub is a repeater with fault detection functionality

• It connects nodes (stations/computers) to LAN

(Ethernet) in star topology

What is a Hub?

 Two pairs (emission and reception)
 Node (station, computer, server,…)
 RJ-45 jack

Hub (10 BASE T)

Node
(host)

Nod

e

(hos

t
)

Hub

• It connects LAN (segment) to another LAN

(segment)

that uses the same protocol (for example, Ethernet

or Token Ring)

• A bridge works at the data-link level of a network,
copying a data frame from one network to the next

network

along the communications path.

• Bridges can make minor changes to the frame

before forwarding it

(such as adding and deleting some fields from the

frame header)

What is a Bridge ?

Bridge

BRIDGES

 Simple Bridge (Connects two LANs)
 Multiport Bridge (Connects more than two LANs)
 Transparent Bridge (learn the Forwarding Table)

 Spanning Tree Bridges (guarantee no loops)

Bridges

-

Bridges are

intermediate systems
(Data Link Layer)
- Operate on Ethernet
frames,
examining MAC
addresses
and selectively
forwarding frame
based on its destination
- Bridge isolates

collision

domains

since it buffers frames.

Repeater vs. Bridge connection

Bridge interconnecting two identical LANs

Bridge interconnecting two dissimilar LANs

A data frame moves

from a CSMA/CD LAN to a Token Ring LAN

BRIDGES

SIMPLE BRIDGE

MULTIPORT BRIDGE

Connection LANs by Bridges

INTERNETWORKING

Remote bridges

can be used to interconnect distant LANs.

Point-to-point line

Remote bridge

LAN C

LAN B

LAN A

Two LANs interconnetion by Frame Relay network

with use remote bridge

•

A network device that selects a path or circuit

for sending a unit of data to its next destination.
• A network device processing packets at layer 2 and 3
– Layer 2 Switch:
• Switches frames at the Data Link Layer
• Uses MAC addresses to determine where frames will be

sended.

– Layer 3 Switch:
• Switches packets at the Network Layer
• Uses IP addresses to determine where packets will be

sended.

What is a Switch?

Switch seperates collision domains

Switch

Collisi

on

Domai

n

Switch

Switch

Coolision Domains

– LAN with collision detection

Broadcating Domain

– max. size of the network, in which frame can be transmit

LAN Switch

 Multiport switching devices

 Distribute broadcating domain into collision domains

Collisi

on

Domai

n

Collisi

on

Domai

n

Collisi

on

Domai

n

Collisi

on

Domai

n

Collisi

on

Domai

n

Fast Link

Hub sending a packet form F to C Switch sending a packet from F to C

Switch sending a frame from F
to a broadcast address

With multicast filtering.
The multicast traffic form F
is only forwarded to selected interfaces.
In this case, only E and H.

Hub vs. Switch functionality

Cut-through vs. Store-and-Forward Switching

DA

SA

PAYLOAD

CRC

incoming
frame

DA

SA

PAYLOAD

CRC

DA

SA

PAYLOAD

CRC

outgoing
frame

48 bit Destination Address + Switching Delay
~30us at 10 Mbit/s

Frame Length + Store-and-Forward Delay
~ 2ms at 10 Mbit/s

outgoing
frame

Frame Switching

Three methods of switching:
- Cut –Through (C-T),
- Store-and-Forward (S-F),
- Inteligent (IS) – hybrid uses C-T or S-F switching.

Workstations connected to a shared segment of a LAN

Workstations connected to a dedicated segment of a LAN

Switch functionality

(simultaneous access to each server)

• Routers determine the next network point
to which a packet should be forwarded
on the way to its final destination

• Routers use the Network Layer Protocol Information
within each packet to "route" it from one destination or

LAN to another.

This means that a router must be able to recognize all

the different devices

that may be used on the networks it is linking together

• Routers communicate with one another
to determine the best route through the complex

connections of many LANs

to increase speed and cut down on network traffic

What is a Router?

Router

ROUTER

LAN A

LAN B

LAN

C

LANs interconnection by Bridge and Router

ROUTERS

Interconnection between LANs and WANs

Switch vs. Router connection

TRANSPORT GATEWAYS AND GATEWAYS

 TRANSPORT GATEWAYS

– Operate at Transport Layer
– Connect two or more station

that use different connection-oriented transport layer

protocols

 GATEWAYS

– Operate at Application Layer
– Translate one format into another

Sieci typu VLAN

(Virtual LAN)

Why VLAN ?

S

a

le

s

M

a

rk

e

ti

n

g

E

n

g

in

e

e

ri

n

g

What is VLAN?



Virtual LAN (VLAN) is a group of devices that can be located anywhere on a network,

but which communicate as if they are on the same physical segment.


With VLANs, we can easily segment your network logically without being restricted

by physical connection

 VLANs ease network changes
It

allow you to group devices as if they are connected by

physical connections.

You do not need to do anyre-cabling.

 VLANs enhance network security

Devices within each VLAN can only communicate with

other devices

on the same VLAN.

 VLANs help control traffic

Increases efficiency by separating traffic from different

groups to prevent

wasting unwanted broadcast/multicast packets.

Benefits of a VLAN

Virtual LANs



VLANs are a logically-independent LANs (which co-exist on

a switch).

It consists of a number of station (computers) that behave

as if they are

in the same collision domain.
 One of the biggest advantages of VLANs
- physically moving a computer to another location:
it can stay on the same VLAN without the need for any

hardware reconfig.

 IEEE 802.1Q is the major protocol for the VLAN.
(Several other proprietary protocols such as Cisco's ISL and

3Com VLT exist)

 Nowadays VLAN configuration tends to reducing the size
of the broadcast domain at the MAC layer.
 Virtual LANs operate at layer 2.
However, administrators often configure a VLAN to map

directly

to an IP network or subnet - involving to layer 3.

A Layer-2 VLANs can be implemented in three ways:

- Open VLANs (use a single MAC address database for all VLANs)
- Closed VLANs (use a separate MAC address database for each VLAN)
- Mixed-Mode VLANs (can be configured as Open or Closed on a VLAN basis)

VLAN - Virtual LAN

LAN  VLAN

 Keep the advantages of Layer 2 interconnection
(addresses, topology - Spanning Tree, switching)
 Enhance with functionalities of Layer 3
(spanning large distances, traffic filtering)
 Limit broadcast domains
 Security (separate sub-networks)
 VLANs build on bridges or switches

explicit & implicit VLAN ID mechanisms

explicit

implicit

tag

headers

MAC

address

switch

port

protocol

type

IP

subnet

Virtual LANs

VLAN can be configured in various ways:

Two methods of establishing a VLAN:



Frame-tagging

It changes the information contained within the layer-2 frame,
so that switches may forward the VLAN traffic to its correct VLAN

destination

and return the frame to its normal format.



Frame-filtering

Frame-filtering involves the switch looking for certain criteria in

the layer-2 frame

and using this matching system to forward the traffic to its

correct VLAN and destination.

Virtual LANs

VLAN Red

= Ports 1,2,7,8

VLAN Blue

= Ports 3,4,5,6

A. VLAN based on ports
(called port-grouped

VLAN)

140.113.200.xxx

1

2

3

4

8

7

6

5

Layer 3

switch

140.113.200.xxx

140.113.200.xxx

140.113.200.xxx

140.113.225.xxx

140.113.225.xxx

140.113.225.xxx

140.113.225.xxx

B. VLAN based on IP subnet

VLAN Red

- Subnet 140.113.200.xxx

VLAN Blue

- Subnet 140.113.225.xxx

1

2

3

4

8

7

6

5

Layer 2
Switch

Virtual LANs



In a switched network, it is difficult to determine the broadcast domain.

 A station may belong to the same or multiple broadcast domain.
 We have to examine configuration files in a VLAN environment to determine
the boundaries of the broadcast domain.

Switched Network

Broadcast Domain 2

Broadcast Domain 1



Although VLANs

A

and

B

are in the same switch,

traffic from VLAN

A

(

B

)

cannot pass directly to VLAN

B

(

A

) within the switch.



Two VLANs will become one large VLAN if a bridge is used to connect them.

 Layer 3 internetworking devices must be used to connect these two VLANs

.

Virtual LANs

VLAN A

VLAN B

Bridge

According to IEEE definition, VLAN is a group of devices
participating in the same Layer 2 domain. All devices in the
domain can communicate with each other without needing to
go through a router.
 Layer 2 switching VLANs
It is based on source / destination MAC address.
 Layer 3 switching VLANs
It is based on both source / destination MAC addresses
and source / destination IP addresses - Multi-Layer
Switching (MLS)
 Layer 4 switching VLANs
It is based on Layer 3 criteria and Layer 4 source /
destination port values.

Virtual LANs

IEEE 802.1Q VLAN Model

Mapping

Redistribution

/resolution

Configuration

Management

information base

VLAN mapping

protocol

request/response

Explicit tagging

Implicit tagging

• special config files in station

• specialised config server

• use of distribution protocol

• frames associated with VLAN

• associations distributed to all

• VLAN Mapping Protocol (VLMP)

• implicit tagging by frame content

• explicit tagging adds new header

IEEE 802.1Q VLAN Frame

Since there are various approaches to create VLANs,
administrators must be carefully handle multi-vendor VLAN.
Due to this deficiency, IEEE develop a vendor-independent method in 802.1Q
to create interoperable VLANs.

802.1Q Frame over Ethernet

TPID - 8 bits, Tag Protocol Identifier (802.1Q Tag Type which is
set to 0x8100)
PRI

- 3 bits, User Priority Field

(8 priorities are defined in

802.1p)
CFI - 1 bit, Canonical Format Indicator
(indicates presence of a Routing Information
Field)
VID - 12 bits, VLAN Identifier (identifies the VLAN)

DA

SA

Tag Len/Type Data

FCS

TPID

PRI

VID

C

F

I

Switch connecting three LANs

Switch using VLAN software

VLAN architectures

Two switches in a backbone using VLAN

VLAN architectures

Single-switch VLAN architecture

Computers can be assigned to VLANs in four ways:

- Port-based VLANs assign computers according to the VLAN switch port
to which they are attached (layer 1)
- MAC-based VLANs assign computers according to each computer’s
data link layer address (layer 2)
- IP-based VLANs assign computers using their IP-address (layer 3)

Multi-switch VLAN architecture