第12章层2交换技术详解.ppt

Slide 1 of 1 Purpose: Emphasize: There are two cost calculation method. The Cat1900 uses the older method. The new method is designed to accommodate the higher gigabits ethernet speed. Note: Port Priority is used to determine which path has preference when path costs are equal. (Example, when you have two parallel links connecting two switches together). The default port priority is 128. Port aggregation protocol and EtherChannels are not taught in this class. Fast EtherChannel is supported by the Cat 1900 switch. Slide 1 of 1 Purpose: Emphasize: Have the students try to work this out. The next slide shows the answers. Slide 1 of 1 Purpose: Emphasize: Switch X and Y has the same path cost to the root bridge. The DP for the bottom segment is on Switch X because Switch X has a lower bridge ID than Switch Y. Slide 1 of 1 Purpose: Emphasize: Using the default STP timers setting, the times it takes to go from the blocking state to the forwarding state is 50 sec (20 + 15 + 15). Slide 1 of 2 Purpose: Emphasize: What will happen if Switch X fails? Slide 2 of 2 Purpose: Emphasize: What will happen if Switch X fails? Switch Y will detect the missing BPDU from Switch X in 20 seconds (max age timer) then recalculate STP. After the network converged, Switch Y will be the root bridge, and all its port will transit to the forwarding states (DP) 30 seconds after the max age timer expires. Slide 1 of 1 Purpose: Emphasize: A layer 2 switch operates just like a bridge by default. Switches use VLANs to solve many of the issues of a large layer 2 environment. Slide 1 of 3 Purpose: Emphasize: Slide 2 of 3 Purpose: Emphasize: In the cut-through mode, the switch checks the destination address (DA) as soon as the header is received and immediately begins forwarding the frame. There is a significant decrease in latency from input port to output port. The delay in cut-through switching remains constant regardless of frame size, because this switching mode star