In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss Cisco Switching Cliff Notes.
Layer 2 Switching
Approximately 20% of your Cisco CCNA exam will be dedicated to Switching. You want to make sure you are well versed in the various terms which will undoubtedly appear on your CCNA exam so you are not caught off guard. Below we will cover the major switching topics you will encounter on your Cisco CCNA exam.
Bridges and Cisco switches are devices that segment or break-up collision domains on a network. They are important components of a network infrastructure and function at the access layer and are definately covered on the CCNA exam. Layer 2 switching is hardware based, it uses MAC addresses to filter the network which results in wire speed, low latency and low cost.
Cisco Switches vs Bridges
Layer 2 Switching
Carrier Sense Multiple Access Collision Detect works as follows:
Switch's three functions at Layer 2
1. Address learning: Associates every received source MAC address with a local port and builds the CAM table(or MAC Table).
2. Forward/filter decisions: If destination MAC address is in the CAM Table and is associated with a port, it will send it to that port; otherwise the frame will be forwarded to all ports except the receiving port.
3. Loop avoidance: Uses STP to avoid loops.
STP is a concept that definately trips people up on their CCNA exam. So take your time in reviewing these concepts.
Non – Root Bridge
Spanning – Tree Port State
Blocking: Won't forward frames; listens to BPDUs. All ports are in this state when the switch is powered up.
Listening: Also listens to BPDUs and makes sure it will not create loops.
Learning: Learns MAC addresses and Builds the CAM table.
Forwarding: Sends and receives data.
LAN Switching Types
Store and Forward: the complete frame is received on the switch’s buffer; a CRC is run, and then forwarded to its destination.
Fragment Free: Checks the first 64 bytes of a frame for fragmentation before forwarding. This would include the preamble, destination address, source address and length.
Cut-through: Once the destination MAC is received (first 13 bytes), the frame is forwarded to its destination. This would include only the preamble and destination address.
Managing Cisco 2950 Switch
switch# show mac-address-table