Tasks of an Ethernet Bridge for Unknown Unicast MAC Addresses
Question
An Ethernet bridge is configured such that all interfaces are in a single broadcast domain. Which two tasks does an Ethernet bridge perform in response to receiving a frame with an unknown unicast destination MAC address? (Choose two.)
Answers
Explanations
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A. B. C. D.BC
When a bridge receives a data frame with an unknown destination MAC address, the frame is flooded out all other ports in the same broadcast domain. Once the bridge sees return traffic from this MAC address, it adds the address to the bridge table.
When an Ethernet bridge receives a frame with an unknown unicast destination MAC address, it performs the following two tasks:
- Flood the frame out of all interfaces except the one on which it was received:
The bridge does not know which interface the destination device is connected to, so it floods the frame out of all interfaces except the one on which it was received. This is known as a broadcast storm. The broadcast storm can cause network congestion and performance issues, so it is important to minimize it.
- Learn the destination MAC address when it sees return traffic from the device:
When the destination device receives the frame, it will send a response back to the source MAC address. The bridge will then learn the MAC address of the destination device and update its forwarding table accordingly. This process is known as MAC address learning.
Once the bridge has learned the MAC address of the destination device, it will forward any subsequent frames destined for that device directly to the appropriate interface, rather than flooding them out of all interfaces.
Therefore, the correct answers to the given question are B (It floods the frame out of all interfaces except the one on which it was received) and C (It learns the destination MAC address when it sees return traffic from the device).
