Transcript Bridge A

Networking Devices
Bridging the gap, switching the
way we communicate, routing us
to new places, repeating what
needs to be stronger – our hub
for communication!
So what devices are there?
The main players:
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Repeaters
Hubs
Bridges
Switches
Routers
Gateways
Repeaters
7 - Application
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6 - Presentation
5 - Session
4 - Transport
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3 - Network
2 – Data Link
1 - Physical
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Simplest networking device
Operates at Layer 1 of the OSI model
Receives a signal, cleans it up, regenerates it
and passes it on
Extends the coverage of a network
Can only be used with similar networks
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i.e. - 2 Ethernet OR 2 token ring NOT Ethernet to
token ring
Can increase network traffic, so must consider
placement and use
Repeater example:
1. Signal sent
Repeater
2. Signal
repeated to
other section
of network
Hubs
7 - Application
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6 - Presentation
5 - Session
4 - Transport
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3 - Network
2 – Data Link
1 - Physical
A central point of connection for many
nodes/network devices
Essentially a repeater with many ports
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Message comes in on 1 port and is then sent out on
all ports to all attached devices
Pass along all data that they receive no matter
where it is addressed to
Hub example:
Hub
Hub receives
message and
send it to all
attached devices
Bridges
7 - Application
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6 - Presentation
5 - Session
4 - Transport
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3 - Network
2 – Data Link
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1 - Physical
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Can be used to split up a large network and
reduce traffic (2 or more segments)
Operates at Layer 2 of the OSI model
Use MAC addresses for sending packets
Creates a bridging table to track locations of
nodes on the network – learn as they go
Performs filtering and (selective) forwarding
Uses the Spanning Tree Protocol (STP)
Types:
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Transparent
Translating
Filtering and Forwarding
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Filtering
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Examines each frame to decide whether it is on
the correct network – this reduces excessive and
unnecessary traffic often created by repeaters
Forwarding
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Sends frames to the segment designated –
(expressed in frames/second)
Higher filtering and forwarding rates are what indicate
the quality and performance of a bridge!
Spanning Tree Protocol (STP)
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Used to decide whether to forward a packet
to another segment
Two purposes:
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Determines the “root” bridge responsible for
decisions and problems
Prevents bridging loops
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If a bridge repeats to one segment and that bridge
were to repeat back to the original segment a “loop”
would be created that would waste valuable resources
and create unnecessary traffic
Spanning Tree Example:
1. Selects Root bridge
2. Designates root ports for forwarding
3. Other ports block traffic to prevent redundancy
Loop free!!!
Bridge A - ROOT
Bridge C
Forwarding ports
Bridge B
X
http://www.kulnet.kuleuven.ac.be/doc/kulnetdoc/kulnetdoc-2001-5.pdf
Blocking port
Types of bridges
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Transparent
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Connect LANs using the same protocol
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Ethernet/Ethernet OR Token ring/Token ring
Translating
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Connect LANs that use different protocols
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Ethernet/Token ring
Translates between the different protocols
Bridge example:
E
F
G
H
#2
Bridge
A
C
#1 #2 #3
B
1. Packet sent
from B to G
#1
D
2. Bridge knows G
is on #2 so only
sends to #2
A
E
I
B
F
J
C
G
K
D
H
L
I
J
#3
K
L
Pareto principle of networks
Segmentation
80% of LAN traffic stays on local LAN
20% of LAN
traffic travels
between LANs
LAN A
bridge
LAN B
Micro-Segmentation
LAN switch
Source: Internetworking Design Strategies: Segmentation, Goldman, Wiley
Switches
7 - Application
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Allow different nodes to communicate directly
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6 - Presentation
5 - Session
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4 - Transport
3- Network
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2 – Data Link
Reduce traffic by creating separate collision
domains
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1 - Physical
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Connect directly by keeping track of the MAC
addresses of each attached device
Connects 2 nodes long enough to transfer the
current packet
Each port on a switch is its own collision domain
Types:
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Cut-through
Store-and-forward
Most switches operates on Level 2 of the OSI model!
Types of switching
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Cut-through
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Read the MAC address
Store the first 6 bytes (address info.)
Sends packet to destination
Store-and-forward
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Reads the entire packet and stores it in the buffer
Performs error checking
Removes bad packets
Sends the packet to destination
Cut-through is faster than store-and-forward!!!
Switch example:
3. Switch looks up
MAC address and
sends to destination
node
Switch
1. Switch receives
message
2. Switch reads all
or part of message
Routers
7 - Application
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6 - Presentation
5 - Session
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4 - Transport
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3- Network
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2 – Data Link
1 - Physical
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Forward data – but are more advanced than
bridges
Operates at Layer 3 of the OSI model
Use IP addresses (not MAC) to send data
Used to interconnect different types of
networks
Connect LAN segments within a building or
even across the country
Create routing tables (using IP info.) in order
to select the best route to send data
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Static or dynamic routing
Various protocols can be used (RIP, IRGP, OSPF,
etc.)
Router example:
A
Routing table #1
Dest.
Path
N
2
N
3,2
Routing table #3
#3
#1
1. Router receives
message from A
for N and consults
routing table
2. Router sends
message through
alternate path due
to traffic (dynamic
routing)
Dest.
Path
A
1
A
2,1
N
#2
Routing table #3
Dest.
Path
A
1
A
3,1
Gateways
7- Application
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Network point (node) that acts as an
entrance/exit to other networks
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Gateway features:
6 - Presentation
5 - Session
4 - Transport
3- Network
2 – Data Link
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1 - Physical
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Protocol translator
Signal translator
Rate converter
Fault isolator
Gateways
7- Application
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6 - Presentation
5 - Session
Equipped for interfacing with another network
that uses different protocols or communication
methods
4 - Transport
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3- Network
2 – Data Link
Example: Countries or continents can use different
methods for digital transmission as long as gateways
are used to connect them
1 - Physical
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Uses Media Gateway Control Protocol
(MGCP) (a.k.a. H.248 and MEGACO)
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Handling the signaling during a multimedia session
Operates at Layer 7 of the OSI model
WLAN#1
Gateway example:
2. Gateway
receives message
and translates the
protocol due to
different protocols
on LAN#1 and
WLAN#1
Makes connection
possible due to
protocol translator!
K
Gateway
/Hot spot
LAN#1
Internet
Internet
A
Gateway
1. Gateway
receives message
from A for K and
consults gateway
routing table
3. Gateway consults
gateway routing
table and sends the
message to K
LAN#2
Gateway
All of these devices come together in order to make up the
networks that we know today. Without these devices the
Internet would not be possible!
Now, let us examine how the Internet actually works
‘Dem bones, ‘dem bones…
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1969: Kai was born/ARPANET commissioned by DoD
1973: ARPANET goes international (satellite link)
1980: ARPA began converting machines to TCP/IP protocol
1983: Transition to TCP/IP completed
1985: NSF got involved in Internet
1986: Backbone called NSFNET was built, and several regional nets
connected to it (speeds of 56Kbps)
1988: NSFNET backbone upgraded to T1 (~1.5Mbps)
1991: NSFNET backbone upgraded to T3 (~45Mbps)
1995: NSFNET reverts back to research network. Traffic now routed
through interconnected network providers
1996: MCI upgrades backbone to 622Mbps
1999: Internet 2 launched.
1999: MCI starts upgrading backbone to 2.5Gbps
Currently, private carriers such as MCI, Sprint, Qwest, and Level(3)
have emerged for carrying Internet traffic. They exchange traffic
between their respective backbones at peering points located in various
major cities around the country.
Source: http://www.zakon.org/robert/internet/timeline/
Internet Backbones
Internet growth
IP Addressing Schemes
CIDR - Classless Internet Domain Routing does away with this
kind of class system in order to allow better use of address space.
Example: 206.13.01.48/25
Domain name addressing
(DNS)
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[email protected]
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Highest level domain: edu, gov, mil, org, etc.
Colorado is a sub-domain within edu
Rastro is a sub-sub-domain within colorado
John is a user in this host machine.
DNS is like a directory enquiry service on the Internet.
IP: Connectionless Delivery System
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Basic transfer unit is called a IP Packet
Packet header
Data Area
•Service is connectionless because each packet is
treated independently of others
•Service is unreliable because delivery not
guaranteed.
•Uses best-effort delivery because the software
makes an earnest attempt to deliver packets.
IP Header Packet format
Routing IP Packets
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Direct delivery between machines in the same
Area or Autonomous System using OSPF.
Indirect delivery between machines in different
Autonomous Systems using BGP.
Hosts and routers maintain routing tables
containing: (network, router) pairs where
network: destination network number
router: address of next router
Default routes used when no entry in the routing
table.
TCP: Transmission Control Protocol
TCP header
Data
TCP is a software protocol which specifies :
 Format of the data and acknowledgements that computers
exchange for reliable and sequenced delivery.
 How to distinguish multiple destinations on a given machine.
 How machines recover from errors like lost or duplicated
packets.
 How two computers initiate a TCP stream transfer and how
they agree it is complete.
Next Generation IP - (Ipv6)
Objectives
 Support billions of hosts.
 Reduce size of routing tables.
 Simplify the protocol for faster routing.
 Provide better security.
 Pay more attention to type of service, especially real-time data.
 Make it possible for host to roam without changing address.
 Allow the protocol to evolve in future.
 Permit the old and new protocols to coexist for years.
 Provide better security than current IP.
 Will maintain compatibility with existing IP protocol.
Source: Tanenbaum, Computer Networks, Prentice-Hall.
IPv6 Fixed header
Version Priority
Flow Label
Payload Length
Next header
Source Address
(128 bits)
Destination Address
(128 bits)
• This is a required header.
• There can also be optional, extension headers.
Hop Limit
Summary
• Bridges and Routers are the mainstays of internetworking.
• Newer devices such as switches emerged in response to need
for higher throughput.
• Several internetworking strategies can be employed to
improve performance.
• Internet has about 400 million hosts* and is still growing
exponentially!
• TCP/IP is the lingua franca of the Internet.
Internet domain survey, January, 2001 -- http://www.isc.org/ds/