Like others, I'm trying to wrap my head around the difference between root ports (I under stand this one) and designated ports (I do not yet understand this one). Wendell Odom's CCNA book mentions the concept of a LAN segment. What exactly is that in the context below? So far I've only read about segments as a synonym for L4PDUs. Is the definition of a LAN segment even relevant to understanding the difference? I know that a designated port cannot be the root port on a non-root switch. But isn't the root port supposed to provide the shortest path to the root switch?
STP/RSTP’s final step to choose the STP/RSTP topology is to choose the designated port on each LAN segment. The designated port (DP) on each LAN segment is the switch port that advertises the lowest-cost Hello onto a LAN segment. When a nonroot switch forwards a Hello, the nonroot switch sets the root cost field in the Hello to that switch’s cost to reach the root. In effect, the switch with the lower cost to reach the root, among all switches con- nected to a segment, becomes the DP on that segment.
Also, what is the point of having the port of one of two switches on both ends of a link be in a blocking state, while the other is in a forwarding state? Doesn't the switch at the blocking end drop all traffic forwarded by the switch with the designated port?