layer 2 and switching. how computers communicate in a two node flat network data can be sent...
TRANSCRIPT
NETWORK FUNDAMENTALS
Layer 2 and Switching
How Computers Communicate
In a two node flat network data can be sent without addressing.
Data only has one path to travel
How Computers Communicate
What if there are more than two nodes on a network?
Like with mail you need to address the data.
In a flat network using a hub this is simple.
How Computers Communicate
Every computer receives all data that is sent and the computer must look at the address to decide what to do with it
To address the data MAC (Media Access Control) addresses are used.
A MAC address identifies the hardware (network card) of a computer on a local network
How Computers Communicate
A MAC address is a group of six two digit hexadecimal numbers
05:AF:2C:19:CF:2B In most cases the first few sets of
numbers represent the make (Dlink, 3Com) and the last numbers represent the specific device
How Hubs Work
All computers in the network are connected to the hub
Computer A
Computer B
Computer C
How Hubs Work
Computer A sends the message “Hello” to Computer C
Computer A
Computer B
Computer C
Hello to C
How Hubs Work
The hub sends the message to all computers connected to it
Computer A
Computer B
Computer C
Hello to C
Hello to C
How Hubs Work
Computer B ignores the message and C replies
Computer A
Computer B
Computer C
Goodbye to A
How Hubs Work
The hub sends the message to all computers connected to it
Computer A
Computer B
Computer C
Goodbye to A
Goodbye to A
How Hubs Work
A receives the message and B ignores the message
Computer A
Computer B
Computer C
Advantages and Disadvantages of Hubs Pros
Simple to buildNo logic needed
ConsCannot handle large amounts of trafficSecurityMore work for the client
Solution to Hubs
Switches solve the problems that hubs have.
Instead of sending the same data out on all ports the switch only sends the data to the port the computer is connected to.
How Switches Work
Switches keep track of which MAC is connected to which port.
Computer A/Port 1
Computer B/Port 2
Computer C/Port 3
How Switches Work
Computer A sends “Hello” to computer B
Computer A/Port 1
Computer B/Port 2
Computer C/Port 3
Hello to B
How Switches Work
The switch looks in the address table and finds B on port 2 and sends the data to the port.
Computer A/Port 1
Computer B/Port 2
Computer C/Port 3
Hello to B
How Switches Work
B receives the data and replies to A.
Computer A/Port 1
Computer B/Port 2
Computer C/Port 3
Goodbye to A
How Switches Work
The switch looks in the switching table and sends the data to A.
Computer A/Port 1
Computer B/Port 2
Computer C/Port 3
Goodbye to A
Advantages and Disadvantages of Switches
ProsMore secureMore efficient Clients only receive data addressed to them
ConsThe switch need logicMore expensive to build
Practice work
List some of the security concerns with using hubs.
List how these do not affect switches. Bonus: How could sniff packets on a
switched network?
There’s not a lot of work that can be assigned at this point.