Specifications

CHAPTER 3
Spanning Tree
Portfast
Portfast is a Cisco-proprietary enhancement to Spanning Tree that helps speed up network convergence. It is for access
(user) ports only. Portfast causes the port to transition directly to forwarding, bypassing the other STP states. Connecting
a switch to a Portfast port can cause loops to develop. Configure Portfast on an interface or interface range:
(config-if)# spanning-tree portfast
It can also be configured globally:
(config)# spanning-tree portfast default
Rapid Spanning Tree
Rapid Spanning Tree (RSTP) 802.1w is a standards-based, nonproprietary way of speeding STP convergence. Switch
ports exchange an explicit handshake when they transition to forwarding. RSTP describes different port states than
regular STP, as shown in Table 3-3.
Table 3-3 Comparing 802.1d and 802.1w Port States
STP Port State Equivalent RSTP Port State
Disabled Discarding
Blocking Discarding
Listening Discarding
Learning Learning
Forwarding Forwarding
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue