Cisco IOS Software Release 12.0
2900#sssshhhhoowoow ww ssssppppaanaannnnnnniiiinngnnggg----ttttrrerreeeeeee bbbbrrirriiieeeeffff Displays the spanning-tree table of the switch
Cisco IOS Software Release 12.1
Switch#sshsshohhooowwww sspsspppaaaannnnnninniiinnnngggg--t--trttrrreeeeeeee Displays the spanning-tree table of the switch
2950#sssshhhhoowoow ww ssssppppaanaannnnnnniiiinngnnggg----ttttrrerreeeeeee iiiinntnnttt f
f ffaaaa 00/00///11117777
Displays spanning-tree info for port fa 0/17 2950#sssshhhhoowoow ww ssssppppaanaannnnnnniiiinngnnggg----ttttrrerreeeeeee vvvvllallaaannnn x Displays spanning-tree
info for the specific VLAN 2950#ddddeeeebbubbuguuggg ssssppappaaannnnnnnniiniinnngggg----ttrttrerreeeeeee {aaaallllllll} Displays all informational messages about changes in the spanning-tree topology
112 Spanning Tree Protocol
Change Spanning-Tree Priority of a Switch
Changing the Cost of Spanning Tree on an Interface
Changing the State of Spanning Tree on an Interface
CAUTION: The command spanning-tree portfast will force a port to move directly to the Forwarding state, without having to transition through the Block-ing, ListenBlock-ing, and Learning states.
This can save up to 50 seconds of wait time. This is an excellent command on access ports that will never be hooked up to another switch. Examples where this would be useful are on ports connected to computers or other end devices, such as printers, servers, and so on. You must exercise caution with this command, however, because if a switch port is plugged into another switch and the portfast command is enabled, then spanning tree will be defeated and a potential switch-ing loop might be created. 24576 or 100 less than current root bridge, whichever
EtherChannel 113
Spanning Tree Portfast BPDU Guard Command
NOTE: There is a feature that has been added to Catalyst IOS called Spanning Tree Portfast BPDU Guard. This feature has been created to maintain stability within the active STP topology. Devices that are attached to ports with Portfast enabled are not allowed to take part in the spanning-tree process. If a port that has Portfast enabled receives a BPDU packet, that port is disabled by the switch. This is done by transitioning the port into the errdisable state. An error message will be sent to the console. Ports disabled by STP BPDU Guard remain in the disabled state unless it is manually enabled with the no shut command or configured to re-enable itself automatically.
Allows port to re-enable itself by setting a recovery timer
Switch(config)#eeeerrrrrrrrddddiiiissassabaabbblllleeee rrrreeeeccccoovoovevveeerrrryyyy i
ii
innnntttteereerrrvvvvaaaall ll 444400000000
Sets recovery timer to 400 seconds.
Default is 300 seconds Switch(config)#sssshhohhooowwww sspsspappaaannnnnnnniiniinnngggg----ttrttrerreeeeeee
s ss
suuuummmmmmammaaarrrryyyy ttottooottttaaaallsllsss
Verifies if BPDU Guard is enabled or disabled
x is the number of the channel-group and must match the other interface
x is the number of the channel-group and must match the other interface
114 EtherChannel
Verification of EtherChannel
EtherChannel Tips
• Can combine from two to eight parallel Ethernet links
• 1900 Switches need 8.00.03 or later Enterprise Edition software
• 2900 Switches need IOS 11.2(8)SA or later
• 2950 Switches need IOS 12.0(5.2)WC(1) or later
• There are three different modes for EtherChannel—auto, desirable, and on :
— auto tells switch to wait for other switch to start EtherChannel negotiations.
If auto is set on both sides, EtherChannel will never form—both sides are waiting for the other side to start negotiating!
— desirable tells switch it is willing to turn EtherChannel on.
— on tells switch it wants to form an EtherChannel.
Only the combinations of auto-desirable, desirable-desirable, and on-on will allow a channel to be formed.
If a device on one side of the channel does not support PAgP, such as a router, the device on the other side must have PAgP set to on.
• All ports must be identical
— Same Speed and Duplex
• Cannot mix Fast Ethernet and Gigabit Ethernet
• Must all be VLAN trunk or non-trunk operational status
Switch#sshsshohhooowwww eeteettthhhheeeerrcrrccchhhhaaaannnnnnenneeellll x ddddeeeettattaaaiiiillll Displays detailed information Switch#sshsshohhooowwww eeteettthhhheeeerrcrrccchhhhaaaannnnnnenneeellll x ppppoooorrtrrttt Displays EtherChannel port
information
Switch#sshsshohhooowwww eeteettthhhheeeerrcrrccchhhhaaaannnnnnenneeellll x ppppoooorrtrrttt----cccchhahhanaannnnnnneeeellll Displays port-channel information Switch#sshsshohhooowwww eeteettthhhheeeerrcrrccchhhhaaaannnnnnenneeellll x ssssuuuummmmmmmmaaaarrrryyyy Displays a one-line summary per
channel-group
CHAPTER 14
VLANs
This chapter provides information and commands concerning the following topics for 1900, 2900, and 2950 series switches:
• Displaying VLAN information
• Creating static VLANs
• Assigning ports to VLANs
• Assigning ports using the range command (2950 series switch only)
• Saving VLAN configurations
• Erasing VLAN configurations
• Troubleshooting VLANs