Module 2 Flashcards
What are the two terms associated with frames entering or leaving an interface?
Ingress: Entering the interface.
Egress: Exiting the interface.
How does a switch forward frames?
A switch forwards frames based on the ingress interface and the destination MAC address, using its MAC address table.
What is the purpose of a switch’s MAC address table?
The MAC address table (or CAM table) records the source MAC address and the port it was received on, helping the switch determine the egress interface for forwarding frames.
What are the two steps in the switch’s Learn and Forward method?
- Learn: Examines the source MAC address and adds it to the MAC address table if not already present.
- Forward: Examines the destination MAC address and forwards the frame out the appropriate port (or floods it if the destination is unknown).
What happens if a switch receives a frame with an unknown destination MAC address?
The switch floods the frame out all interfaces except the ingress port.
What are the two main switching methods used by switches?
- Store-and-forward switching: Receives the entire frame, checks for errors, and then forwards it.
- Cut-through switching: Forwards the frame immediately after determining the destination MAC address.
What is the difference between store-and-forward and cut-through switching?
- Store-and-forward: Checks the entire frame for errors (e.g., CRC) and buffers it before forwarding.
- Cut-through: Forwards the frame immediately after reading the destination MAC, without error checking.
What are the characteristics of store-and-forward switching?
- Error Checking: Verifies the Frame Check Sequence (FCS) for CRC errors.
- Buffering: Temporarily stores the frame while checking for errors and adjusting for speed differences between ports.
What is the Fragment-Free method in cut-through switching?
It checks that the frame is at least 64 bytes (to eliminate ‘runts’) before forwarding it.
What are the advantages and disadvantages of cut-through switching?
- Advantages: Low latency (under 10 microseconds).
- Disadvantages: Does not check for errors, may propagate errors, and cannot support ports with differing speeds.
What is a collision domain?
A network segment where collisions can occur, typically in half-duplex mode.
How does a switch handle collision domains?
Switches eliminate collision domains by using full-duplex links, where each port operates independently.
What is a broadcast domain?
A network segment where broadcast traffic is forwarded, extending across all Layer 1 or Layer 2 devices.
How can a broadcast domain be broken?
A broadcast domain can be broken by a Layer 3 device (e.g., a router), which does not forward broadcast traffic.
What happens when a switch receives a broadcast frame?
The switch floods the broadcast frame out all interfaces except the ingress port.
What are the effects of too many broadcasts in a network?
Too many broadcasts can cause congestion and poor network performance.
What happens if a switch connection has a duplex mismatch?
If one interface is in half-duplex, a collision domain is created on that link, even with a switch.
What are the features of switches that alleviate network congestion?
- Fast port speeds (up to 100Gbps).
- Fast internal switching for improved performance.
- Large frame buffers for temporary storage.
- High port density for connecting more devices with less congestion.
What is the difference between a routing table and a MAC address table?
- Routing table: Used by Layer 3 devices (e.g., routers) to forward packets based on IP addresses.
- MAC address table: Used by Layer 2 devices (e.g., switches) to forward frames based on MAC addresses.
What are the three actions a Layer 2 switch can perform with frames?
- Flood: If it’s a broadcast or the unicast destination is unknown.
- Forward: If the unicast destination is in the MAC table.
- Filter: If the source and destination are on the same port.
What creates a collision domain, and how is it resolved?
- Cause: Extending the network at Layer 1 (e.g., adding hubs in half-duplex mode).
- Solution: Using Layer 2 switches in full-duplex mode to eliminate collision domains.
What causes a broadcast domain, and how is it resolved?
- Cause: Extending the network at Layer 1 or Layer 2 (e.g., hubs or switches flooding traffic).
- Solution: Using Layer 3 devices (e.g., routers) to break broadcast domains.
What would happen if Layer 3 devices passed broadcasts?
Broadcasts would propagate across networks, causing congestion and inefficient use of bandwidth.
What is the difference between a Layer 1 hub, a Layer 2 switch, and a Layer 3 router?
- Layer 1 hub: Floods traffic to all ports.
- Layer 2 switch: Forwards traffic based on MAC addresses, floods broadcasts, and filters traffic when source and destination are on the same port.
- Layer 3 router: Forwards traffic based on IP addresses and does not flood broadcasts.
Compare store-and-forward and cut-through switching in terms of error handling.
- Store-and-forward: Eliminates CRC errors, runts, and giants.
- Cut-through (Fragment-Free): Only eliminates runts.
