Switches 1RD-CSY1017

2  In this lecture, we will learn about  Collision Domain and Microsegmentation  Switches – a layer two device ◦ MAC address Table ◦ Frame Filtering ◦ Frame Forwarding ◦ Frame Buffering ◦ Full Duplexing  Collision domain in switches

 A collision domain is a logical area in a computer network in which data packets can collide with one another. A collision occurs when two or more devices attempt to send a signal along the same transmission channel (e.g., the same section of copper wire or optical fiber) simultaneously.  Disadvantages of data collisions are: ◦ Decreased network efficiency ◦ Packet Loss. ◦ Slow Performance of the network. ◦ More bandwidth utilization  Network devices are used to reduce the size of network segment or Collision domain. ◦ Layer 3 device: Router ◦ Layer 2 device: Switch and bridge RD-CSY10173

 Switches reduce the size of collision domain  Microsegmentation is the dividing of a network through the use of network switches such that only two nodes coexist within each collision domain. RD-CSY10174

5 hub switch router Collision Domains

RD-CSY10176  Layer 2 Multiport device ◦ E.g., 12 ports, 24 ports, 48 ports  Switches are specified by number of ports and bandwidth supported ◦ 10/100 Mbps ports  connecting computers in a network. Port

RD-CSY10177  Switches associate MAC addresses with port numbers and store them in its memory in a table called MAC Address Table  Whenever a frame enters a switch, it will add Source Address (1111) against port number (2) through which it came in is in it’s table.  This table for catalyst switches is called CAM (Content Addressable Memory) table  The CAM table times out every 5 minutes Source Address Table Port Source MAC Add switch

RD-CSY10178 Source Address Table Port Source MAC Add  Switches output a frame on a specific destination port.  Switch examines the MAC address table for the Destination MAC address.  If it finds a match, it filters the frame by only sending it out on that port. ◦ If no match is found, it floods it out on all the ports.  switch Sample MAC addresses

RD-CSY10179  PC 3333 wants to send data back to  The switch now has an entry for the Source Address (3333) ◦ It does NOT add it.  It checks the Destination Address, it has it in its table  As both MAC addresses are in the switch’s table, information exchanged between 1111 and 3333 can be filtered out the appropriate port (port 8) and not Flooded switch MAC Address Table Port Source MAC Address

RD-CSY when two devices (1111 and 2222) send to same destination (3333)? The switch buffers the frames and sends them out on port number 7 one at a time.

RD-CSY  Full-duplex allows simultaneous (send and receive at the same time) communication between a pair of devices.  Both ends of the link must be in full-duplex mode.  Most switches operate at either full-duplex but can operate in half- duplex.

RD-CSY For every frame that enters a switch…  Learning Stage (Building/Updating of MAC table) ◦ Examines Source MAC Address:  If Source MAC Address is in the MAC table, update 5 minute timer  If Source MAC Address is NOT in the MAC table, add Source MAC Address and incoming port number to MAC table  Forwarding Stage (Flood or Filter) ◦ Examines Destination MAC Address:  If Destination MAC Address is in the MAC table, forward the frame only out that port (Filter),  If Destination MAC Address is NOT in the MAC table, forward the frame only out all ports except incoming port (Flood)

RD-CSY  Switches have multiple collision domains.  To communicate with all collision domains, broadcast and multicast frames are used at Layer 2.  Every NIC must recognize this address  Since broadcasts generate excess traffic in the network, broadcasts must be controlled.  Devices such as router which operate at Layer 3 control broadcasts.

RD-CSY  Five new terms that you learnt in this session

 Find information about switches available in the lab ◦ Cisco 2950 switches ◦ Cisco 3560 switches  Compare their features  Hardware options possible  Memory –RAM/Flash  IOS images supported  Applications of switches  Find the differences between Layer 2 /Layer 3 Switches 15RD-CSY1017