As frames arrive upon switch ports, the source MAC addresses are learned and recorded in the CAM table, along with the port of arrival, the VLAN, and a timestamp.If a MAC address learned upon a port has moved to another port, the MAC address and timestamp are recorded for the most recent port; and then the previous entry is deleted.
When a frame arrives at a switch port, it is placed into one of the ports ingress queue. Each queue contain frames to be forwarded , with each queue have different priority and service level. Critical data loss can be avoided by fine tuning the switch port so the important frames get processed and forwarded first.As ingress queues are serviced and a frame is pulled off the switch must figure out not only where the forward the frame but also whether it should be forwarded and how ?
Layer 2 forwarding table(CAM) :
The frame destination MAC address is used as an index or key into the CAM table(content addressable memory). CAM table has three three rows - MAC address, Egress port and VLAN. If the address is found, egress switch port and appropriate VLAN ID are read from the table.
Ternary Content addressable memory (TCAM) :
*Securing ACL - ACL can be used to identify frames according to their MAC address , protocol,IP address and layer 4 port numbers. TCAM's carry ACL's in compiled form so that a decision can be made on whether to forward a frame in a single table lookup.
*QOS ACL - Other ACL's which are used to classify incoming frames according to quality of service parameters, to control the rate of traffic flows and to mark QOS parameters in outbound frames.
In the next blog lets follow a packet :)
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