What IEEE 802.1D Spanning Tree Does
STP prevents loops by placing each switch port in either a forwarding state or a blocking state. Interfaces in the forwarding state act as normal, forwarding and receiving frames. However, interfaces in a blocking state do not process any frames except STP messages (and some other overhead messages). Interfaces that block do not forward user frames, do not learn MAC addresses of received frames, and do not process received user frames.
Figure 11-2 shows a simple STP tree that solves the problem shown in Figure 11-1 by placing one port on SW3 in the blocking state.
Figure 11-2 What STP Does: Blocks a Port to ...
Get CCNA Data Center DCICN 640-911 Official Cert Guide now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
