Yet more Spanning Tree

Spanning-tree portfastome Cisco enhancements to STP are:

Portfast is a feature that skips the listening and learning states and the interface goes straight to forwarding, reducing the amount of time it takes for a port to come online.  This is useful when plugging in an end user device, such as a PC or phone.  However, if you plug in a switch or hub, you are going to want to enable BPDU Guard.

BPDU guard disables a portfast-enabled port if it receives a BPDU packet on that interface.  This way we avoid loops that would normally be discovered during the listening delay.

Uplinkfast is similar to portfast, but its use is in networks where there is a redundant uplink to from access-layer switches to core.  When a known uplink port goes offline, the second link will skip the listening and learning states and go straight to forwarding.

Backbonefast is similar to uplinkfast, however the access-layer switch does not have direct knowledge of the link failure, rather it exists between distribution switches.  Once the link between distribution switches goes offline, both think they are the root bridge and start advertising as such.  When the access layer switch forwards the distribution layer BPDU to the other distribution switch, it realizes it has a path to replace the link between switches and the topology converges.

These are all features of spanning-tree and their commands are:

R1(config-if)#spanning-tree portfast
R1(config-if)#spanning-tree bpduguard enable
R1(config-if)#spanning-tree uplinkfast
R1(config-if)#spanning-tree backbonefast

Or to enable BPDU guard globally, enter:

R1(config)#spanning-tree portfast bpduguard default

And you can tell if STP is configured on your switch by using:

R1# sho spanning-tree summary

Etherchannel is not necessarily a spanning tree enhancement, but is a means to utilize multiple links between switches.  Etherchannel will take up to 8 links and load balance across them in stead of disabling the extra links to avoid loops.  The ports must all be configured with the same speed and duplex to participate.  If one of the links in an etherchannel goes offline, the switch will still utilize the remaining ports and load balance accordingly.  To create an etherchannel, enter into each interface to participate in the etherchannel and use the channel-group <x> mode on command.  Cisco IOS then creates a logical interface called a port-channel interface so that parameters can be set on the entire port-channel from one location.