Ethernet Switch

1) Switches are the next evolution of bridges and the operation they perform is still considered bridging. In very basic terms a switch is a high port-count bridge that is able to make decisions on a port-by-port basis.

2) A switch maintains a MAC table and only forwards frames to the appropriate port based on the destination MAC.

3) If the switch has not yet learned the destination MAC it will flood the frame. (I've read some data that says it'll use arp to know the MAC.)

Q: How to collect the MAC Table?
A: Each end-point is labeled with a MAC address starting with AF:AF:AF:AF:AF.  The ‘dynamic learning’ is done be recording the source MAC address of incoming frames.  While the destination MAC address had not yet been learned, the switch would be forced to flood the frame to all ports except the one it received.


Ref.:
http://en.wikipedia.org/wiki/Network_switch
http://www.definethecloud.net/data-center-101-local-area-network-switching/

Bridge

1) A bridge is a device that connects two or more local area networks, or two or more segments of the same network.

2) The original bridges were typically 2 or more ports (low port counts) and could separate MAC addresses using the table for those ports.

3) In the OSI model bridging acts in the first two layers, below the network layer.


Q: How to make a bridge table?
A:

Ref.:
http://en.wikipedia.org/wiki/Bridging_(networking)
http://www.definethecloud.net/data-center-101-local-area-network-switching/
http://technet.microsoft.com/en-us/library/cc700841.aspx

Hub

1) It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming.

2) A hub works at the physical layer (layer 1) of the OSI model

3) There's 2 kinds of hub, Passive & Active (which needs adapter & it'll repeat the signals)


Ref.:
http://en.wikipedia.org/wiki/Ethernet_hub
http://www.definethecloud.net/data-center-101-local-area-network-switching/

Internetworking

Device	PHY	Data Link	Network	Others
Repeater	Same	Same	Same	Same
Hub	Same	Same	Same	Same
Bridge	Same/!Same	Same/!Same	Same	Same
L2 Switch	Same/!Same	Same	Same	Same
Router	Same/!Same	Same/!Same	Same	Same
L3 Switch	Same/!Same	Same/!Same	Same	Same
Gateway	Same/!Same	Same/!Same	Same/!Same	Same/!Same

OSI Model
	Data unit	Layer	Function
Host layers	Data	7. Application	Network process to application
		6. Presentation	Data representation, encryption and decryption, convert machine dependent data to machine independent data
		5. Session	Interhost communication, managing sessions between applications
	Segments	4. Transport	Reliable delivery of packets between points on a network.
Media layers	Packet/ Datagram	3. Network	Addressing, routing and (not necessarily reliable) delivery of datagrams between points on a network.
	Bit/Frame	2. Data link	A reliable direct point-to-point data connection.
	Bit	1. Physical	A (not necessarily reliable) direct point-to-point data connection.

Ref.:
http://www.cs.nthu.edu.tw/~nfhuang/chap14.htm
http://en.wikipedia.org/wiki/OSI_model