In a Layer 2 switch bridging between a 1000BASE-T port and a 100Base-T network, which buffering approach is recommended?

• A. Port-Based Buffering
• B. Level 1 Cache Buffering
• C. Shared Memory Buffering
• D. Fixed Configuration Buffering

Answer: (C)

When a Layer 2 switch bridges between a faster 1 Gbps port and a slower 100 Mbps network, there’s a natural burst risk as frames arrive faster than they can be sent out. The best way to handle this is to have a flexible buffering system that can be shared among all ports, so bursts on the fast side can be absorbed without dropping frames or starving other ports.

Shared memory buffering provides a common pool of buffers that any port can use. This lets the switch temporarily store incoming frames from the 1 Gbps side and then relay them to the 100 Mbps side at its slower rate, while also accommodating bursts in the opposite direction if needed. The key advantage is efficient reuse of buffer space across the entire switch, rather than locking buffers to a single port or keeping a rigid, per-port capacity.

Per-port buffering ties a fixed amount of memory to each individual port, which can lead to insufficient buffering when one port experiences a burst and another is idle. A small port-local cache can fill quickly during a surge and still not provide enough headroom. Fixed configuration buffering lacks the adaptability to changing traffic patterns, making it less capable of handling mismatched speeds gracefully.

In short, shared memory buffering offers the needed flexibility and efficiency to balance traffic between a gigabit port and a fast Ethernet network.