Switching concepts
1 Frame fowarding
Switching in networking
Various types of switches used in LANs, WANs and public switched telephone
network (PSTN)
How switch fowards traffic -> based on flow of traffic
Two associated terms with frames entering and leaving device
Ingress = used to describe port where frame enters device
Egress = used to describe port that frames use when leaving device
LAN switch maintains table referenced when forwarding traffic through switch
Ethernet frame never forwarded out same port on where it was received
Switch MAC address table
Switches use MAC addresses to direct network communications through switch
(out a port, toward destination)
Switch must know which devices exist on each port to transmit frame
-> build by switch
-> stored in Content Addressable Memory (CAM, special type of memory
used in high-speed searching applications)
-> used by LAN switches to determine how to handle incoming data frames
Switch learn and forward method
Step 1: learn – examining source MAC address
Every frame that enters switch -> checked for new information to learn
If source MAC address does not exist => MAC address and incoming port
number -> added to table
If source MAC address does exist => switch updates refresh timer for
entry, entry is replaced using same MAC address with current port number
Step 2: forward – examing destination MAC address
If destination MAC address = unicast address, switch will look for match between
destination MAC of frame and entry in MAC address table
- If destination MAC address is in table -> forward frame out of port
- If destination MAC address isn’t in table -> switch will forward frame out of
all ports except incoming port (= unknown unicast) , same for broadcast or
multicast
Switching forwarding methods
Application-specific-integrated circuits (ASICs) = reduce frame-handling time
within device and allow device to manage increased number of frames without
degrading performance
Layer 2 switches use one of 2 methods to swith frames:
1 Frame fowarding
Switching in networking
Various types of switches used in LANs, WANs and public switched telephone
network (PSTN)
How switch fowards traffic -> based on flow of traffic
Two associated terms with frames entering and leaving device
Ingress = used to describe port where frame enters device
Egress = used to describe port that frames use when leaving device
LAN switch maintains table referenced when forwarding traffic through switch
Ethernet frame never forwarded out same port on where it was received
Switch MAC address table
Switches use MAC addresses to direct network communications through switch
(out a port, toward destination)
Switch must know which devices exist on each port to transmit frame
-> build by switch
-> stored in Content Addressable Memory (CAM, special type of memory
used in high-speed searching applications)
-> used by LAN switches to determine how to handle incoming data frames
Switch learn and forward method
Step 1: learn – examining source MAC address
Every frame that enters switch -> checked for new information to learn
If source MAC address does not exist => MAC address and incoming port
number -> added to table
If source MAC address does exist => switch updates refresh timer for
entry, entry is replaced using same MAC address with current port number
Step 2: forward – examing destination MAC address
If destination MAC address = unicast address, switch will look for match between
destination MAC of frame and entry in MAC address table
- If destination MAC address is in table -> forward frame out of port
- If destination MAC address isn’t in table -> switch will forward frame out of
all ports except incoming port (= unknown unicast) , same for broadcast or
multicast
Switching forwarding methods
Application-specific-integrated circuits (ASICs) = reduce frame-handling time
within device and allow device to manage increased number of frames without
degrading performance
Layer 2 switches use one of 2 methods to swith frames:
