Advanced STP

To enable Etherchannel, enter this command into each required sub-interface:channel-group number mode onEvery interface in the etherchannel must have the same number.The neighbour switch can use a different number

Etherchannel show commands:show spanning-tree [vlan-id]show etherchannel x summary

There are 2 different types of Dynamic Etherchannel:PAgP - Port Aggregation ProtocolLACP - Link Aggregation Control Protocol

To setup PAgP on an interface:channel-group 1 mode desirableOther side can use:channel-group 1 mode desirable, or:channel-group 1 mode auto

To setup LACP on an interface:channel-group 1 mode activeOther side can use:channel-group 1 mode active, or:channel-group 1 mode passive

For both PAgP and LACP, at least one side of the Etherchannel must be set to desirable/active.This side of the Etherchannel begins negotiations.

Using default Etherchannel (channel-group 1 mode on) on one side and PAgP or LACP on the other will not work.

To Determine the Root Switch:

1. From a list or diagram, consider all as a possible root switch

2. Any switch with a root port is not the root switch (root switches only have designated ports):show spanning-treeshow spanning-tree root

3. show spanning-tree will say if the current switch is the root

4. show spanning-tree root will indirectly say if the switch is the root.if the switch is the root, the RP column will be blank.

5. In a simulation question, follow the root ports to find the root switch.

6. In a simulation question, use show spanning-tree vlan x on a few switches

Tie breakers when choosing a root port:1. Neighbour with the lowest BID2. Neighbour with the lowest port priority3. lowest neighbour internal port number

Port priority is set to 128 by default.This can be set to anything from 0 to 255 (lowest is best priority), using:spanning-tree vlan 10 port-priority 100

STP CONVERGENCE

- Interfaces that are staying in the same STP state do not change

- For interfaces that need to change from forwarding to blocking, the switch immediately puts the port into blocking state

- For interfaces that need to change from blocking to forwarding, the switch first puts the port into listening, and then learning.Length of time in each state is determined by the forward delay timer

show etherchannel summary

Etherchannel

STP Troubleshooting

stp convergence