objectives after completing this chapter you will be able to: describe the different types of...
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Objectives
After completing this chapter you will be able to:
Describe the different types of bridging: Transparent, Source Route and Translate
Describe how Transparent Bridges operateOutline the advantages and disadvantages of bridgingDescribe the fundamentals of LAN switches
OSI Model
Repeater
Bridge
Router
Data
Data
Data
Data
101100011110101010010
Data
DataT
A
N
S
P
D
Data
Data
Data
Data
101100011110101010010
Data
DataT
A
N
S
P
D
SYSTEM A SYSTEM B
Repeaters v Routers / Bridges v Routers
REPEATER
Single Broadcast DomainSingle Collision Domain
Network Segment A
C.D. B.D.
BRIDGE orSWITCH
Single Broadcast DomainTwo Separate Collision Domains
Network Segment A
C.D. B.D.
ROUTER
Two Separate Broadcast DomainsTwo Separate Collision Domains
Network Segment A
C.D. B.D.Network Segment A Network Segment B Network Segment B
Different Types of Bridging
Source Route BridgesDeveloped by IBM for use in Token Ring Networks.
The entire route to a destination is predetermined prior to sending data.
Transparent Bridges
Developed by Digital Equipment Corporation (DEC) for use in Ethernet
networks.Frames are forwarded one hop at a time towards the destination
Source Route Bridging
2
3
1
4
5
6
7
8
Discovery
Response
Transparent Bridging
Source Address tableAddress Interface
1 A2 A3 A4 B5 B6 B7 C8 C9 C
A
B 6
5
4
2
3
1BRIDGE
9
8
7
C
Transparent Bridge Operation - Example
AB
6
5
4
2
3
1
BRIDGE
9
8
7
C
Source 1 - Destination 4
Source 4 - Destination 1
Bridging Loops
Packet with unknown destination
Bridge 1 Bridge 2
Preventing Loops
FORWARDING
BLOCKING
FORWARDING
FORWARDING
Packet with unknown destination
Spanning Tree Protocol
A C
JI
H
FEG
D
B2 31 4
98
765
Root Bridge
BLOCKING
LAN
Bridge
Symbols:
Comparison of Source Route and Transparent Bridges
Transparent bridges are connection-less whereas source-route bridging provides connection-oriented networking.
Transparent bridges are completely invisible to the hosts and are fully compatible with all existing 802 products.
With Source-Route bridging, the network manager must manually install the LAN and bridge numbers.
One of the few advantages of source-route bridging is that, in theory, it can use optimal routing.
Source route bridges are more expensive, especially if they use VLSI chips in their interface cards.
Transparent bridges learn about bridge and LAN failures and other topology changes quickly and automatically.
LAN Switches
High Speed Backplane
Switch
HUB
Each network device, for example, a file server, has dedicated bandwidth.
VLANs
Switch
HUB
HUBHUB HUB
Advantages of Bridging
Bridges can connect networks running different protocols without requiring additional software.
Bridges form logically single networks. A bridge makes the movement of network devices, e.g. PCs, within the network easy.
Bridges are simple to install.Bridges are cheaper than routers.The presence of a bridge is transparent to users from the
instant it is first installed, and bridges adapt automatically to network changes.
Disadvantages of Bridging
Bridges cannot load-share traffic over two paths to a single destination, because the STA ensures that one of these paths will block all traffic.
Bridges cannot prevent a ‘broadcast storm’.Bridges do not provide significant support for fault
isolation or other distributed management capabilities.
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