LAN: Internetworking

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26 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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Chapter 8:

Local Area Networks: Internetworking

2



Objectives







List the reasons for interconnecting multiple local area
network segments and interconnecting local area
networks and wide area networks


Identify the functions and purposes of the various
interconnection devices that have been used over time


Define a hub and describe the situations in which a
hub is used


Describe how a transparent bridge learns

3



Objectives (continued)







Describe what a switch is and how it differs from other
devices


Describe the types of situations in which using a
switch is advantageous


Describe what a router is and how it differs from other
devices


Describe the types of situations in which a router is
used

4



Introduction







Sometimes necessary to connect local area network to
another LAN or to wide area network


Local area network to local area network connections
often performed with bridge
-
like device


Local area network to wide area network connections
usually performed with router


Switch
-

can be used to interconnect segments of a local area
network

5



Why Segment or Internetwork Local




Area Networks?







To separate / connect one corporate division with
another


To connect two LANs with different protocols


To connect a LAN to the Internet


To break a LAN into segments to relieve traffic
congestion


To provide a security wall between two different types
of users

6



Hubs







Hub

-

interconnects two or more workstations into a local area
network


When workstation transmits to a hub


Hub immediately resends data frame out to all connecting
links


Hub can be managed or unmanaged


Managed hub possesses enough processing power that it can
be managed from a remote location

7



Bridges







A bridge (or bridge
-
like device)



Can be used to connect two similar LANs, such as two
CSMA/CD LANs


Can also be used to connect two closely similar LANs, such
as a CSMA/CD LAN and a token ring LAN


Examines destination address in a frame


Either forwards this frame onto next LAN or does not


Examines source address in frame


Places this address in a routing table to be used for future
routing decisions

8



Bridges (continued)






9



Transparent Bridge







Does not need programming


Observes all traffic


builds routing tables


This observation is called backward learning


Each bridge has two connections (ports)


Routing table associated with each port

10



Transparent Bridge (continued)







Bridge


Observes each frame that arrives at port


Extracts the source address from the frame


Places that address in the port’s routing table


Transparent bridge is found with CSMA/CD LANs

11



Transparent Bridge (continued)






12



Transparent Bridge (continued)






13



Transparent Bridge (continued)







Transparent bridge can also convert one frame format
to another


Note that some people / manufacturers call this kind of
bridge a gateway or router


Bridge


Removes headers and trailers from one frame format


Inserts (encapsulates) headers and trailers for second frame
format

14



Remote Bridge







Capable of passing data frame from one local area
network to another when


Two LANs are separated by long distance


There is a wide area network connecting the two LANs


Remote bridge takes the frame before it leaves the first
LAN



Encapsulates the WAN headers and trailers


When packet arrives at destination remote bridge


that bridge removes the WAN headers and trailers
leaving original frame

15



Remote Bridge (continued)






16



Switches







Combination of hub and bridge


Can interconnect two or more workstations


Like bridge, it observes traffic flow and learns


When a frame arrives at a switch, the switch


Examines destination address


Forwards frame out the one necessary connection


Workstations that connect to


Hub


on shared segment


Switch


on switched segment

17



Switches (continued)






18



Switches (continued)







Backplane of a switch is fast enough to support
multiple data transfers at one time


A switch that employs cut
-
through architecture is
passing on the frame before the entire frame has arrived
at the switch

19



Switches (continued)







Multiple workstations connected to a switch use
dedicated segments


Very efficient way to isolate heavy users from the network


A switch can allow simultaneous access to multiple
servers, or multiple simultaneous connections to a
single server

20



Switches (continued)





21



Isolating Traffic Patterns and Providing





Multiple Access






22



Isolating Traffic Patterns and Providing




Multiple Access (continued)






23



Isolating Traffic Patterns and Providing




Multiple Access (continued)






24



Isolating Traffic Patterns and Providing




Multiple Access (continued)






25



Full
-
Duplex Switches







Allows for simultaneous transmission and reception of
data to and from a workstation


This full duplex connection helps eliminate collisions


To support a full duplex connection to a switch, at
least two pairs of wires are necessary



One for the receive operation


One for the transmit operation


Most people install four pairs today, so wiring is not
problem

26



Full
-
Duplex Switches (continued)






27



Network Servers







Network servers provide necessary storage for LAN
software


Usually focal point for network operating system


Increasingly, network servers are functioning as
bridges, switches, and routers


By adding appropriate card, a server can assume
multiple functions

28



Routers






Router
-

device that connects a LAN to a WAN or a WAN
to a WAN


Router:

1.
Accepts outgoing packet

2.
Removes any LAN headers and trailers

3.
Encapsulates necessary WAN headers and trailers


Because router has to make wide area network
routing decisions


r
outer has to dig down into the
network layer of the packet to retrieve network
destination address

29



Routers (continued)







Routers are often called “layer 3 devices”


Operate at the third layer, or OSI network layer, of the
packet


Often incorporate firewall functions

30



Routers (continued)






31



LAN Internetworking in Action:



A Small Office Revisited







Recall In Action example from Chapter Seven


A small office with 20 workstations in one room and
15 workstations in another room were connected to a
server via 100BaseTX


One hub was kept in a closet near the 20 workstations
while a second hub was near the server

32




LAN Internetworking in Action:



A Small Office Revisited (continued)






33



LAN Internetworking in Action:



A Small Office Revisited (continued)






Now Hannah wants to connect the LAN to the Internet


She adds a router next to the server and connects it to
the hub


She connects the router to a high
-
speed telephone line
such as a T
-
1 service


She will also have to program the router to perform IP
addressing and firewall functions

34




LAN Internetworking in Action:



A Small Office Revisited (continued)






35




LAN Internetworking in Action:



A Small Office Revisited (continued)







Now network usage is so high that Hannah must
consider segmenting the network


She decides to install a database server near the
original server and replace both hubs with switches

36



LAN Internetworking in Action:



A Small Office Revisited (continued)






37



Summary







Interconnecting multiple LAN segments as well as
LANs and WANs


Interconnection devices


Hubs


Transparent bridges


Switches


Routers