Building Ethernet LANs with Switches Flashcards
What does CSMA/CD stand for?
Carrier Sense Multiple Access with Collision Detection
LAN switches receive Ethernet frames and then make a switching decision: either forward the frame out some other port(s) or ignore the frame. To accomplish this primary mission switches perform what three actions?
- Deciding when to forward a frame or when to filter (not forward) a frame, based on the destination MAC address.
- Learning MAC address by examining the source MAC address of each frame received by the switch.
- Creating a (Layer 2) loop-free environment with other switches by using Spanning Tree Protocol (STP)
Swithces build the address table by listening to incoming frames and examining the ______ ______ ______ in the frame.
source MAC address
Switches keep a timer for each entry in the MAC address table, called an ______ ______.
inactivty timer
When thers is no matching entry in the table, switches forward the frame out all interfaces (except the incoming interface) using a process called _________.
flooding
Spanning Tree Protocol causes each interface on a switch to settle into either a _______ state or a _______ state.
blocking or forwarding
__________ means that the interface cannot forward or receive data frames
blocking
_________ means that the interface can send and receive data frames.
forwarding
With _____-_____ processing, the switch starts sending the frame out the output port as soon as possiable.
cut-through
______-____ ______ works similarly to cut-through, but it tries to reduce the number of errored frames that it forwards.
Fragment-free processing
The switch fully recieves all bits in the frame (store) before forwarding the frame (forward). This allows the switch to check the FCS before forwarding the frame.
Store-and-forward
The switch forwards the frame as soon as it can. This reduces latency but does not allow the switch to descard frames that fail the FCS check.
Cut-through
The switch forwards the frame after receving the first 64 bytes of the frame, thereby avoiding forwarding frames that were errored because of a collision.
Fragment-free
What are four benefits of using LAN switches?
- Switch ports connected to a single device microsegment the LAN, providing dedicated bandwidth to the single device.
- Switches allow multiple simultaneous conversations between devices on different ports.
- Switch ports connected to a single device support full-duplex, in effect doubling the amount of bandwidth available to the device
- Switches support rate adaptation, which means that devices that use different Ethernet speeds can communicate through the switch (hubs cannot)
Why do switches use STP?
Switches use STP to prevnet loops by causing some interfaces to block, meaning that they do not send or receive frames.