Enabling Spanning-tree on an active switch

MartinScarrow,

 

Enabling STP globally and then applying STP to the port-channels without causing downtime is possible, but it depends on how you configure it.

 

Here's a step-by-step approach you can follow:

 

1. Enable STP globally on both switches:
spanning-tree mode rstp

 

This will enable RSTP (Rapid Spanning Tree Protocol) globally on both switches.

2. Configure the STP priority:
spanning-tree rstp priority 61440

 

This sets the STP priority to a default value of 61440, which is a good starting point.

3. Configure the STP mode for the port-channels:
spanning-tree port-channel *channel_number* mode edge

 

Replace channel_number with the actual number of the port-channel you want to configure. This command enables STP on the port-channel and sets the mode to "edge", which means that the port-channel will become a leaf node in the STP topology.

Here's an example:
spanning-tree port-channel 1 mode edge

 

This command enables STP on port-channel 1 and sets it to "edge" mode.

When you enable STP globally and then apply STP to the port-channels, the switches will go through a transition phase before reaching forwarding mode. During this transition, the port-channels may go through a brief period of blocking, but this should not cause any downtime.

 

 

Let me know if this helps.

 

 

Hi Chris

Thank you for replying.

So to clarify, as the two switches already have the following configuration on them:

spanning-tree mode rstp
spanning-tree rstp priority 61440
spanning-tree disable

I can go in to the port-channel interface and add spanning-tree:

conf t 
interface port-channel10
spanning-tree port type edge

Once applied to all port-channels, I can enable spanning-tree

conf t
no spanning-tree disable

I can monitor the port-channel status via this command:

show spanning-tree brief | grep port-channel

The questions I have are:

• As one switch will have spanning-tree enabled and the other doesn't at this point will this cause an issue, due to the blade servers having a connection to both switches, I just need to make sure that the servers have at least one connection to a switch.
•  This follows on to when I enable spanning-tree on the second switch, they wont suddenly start blocking both port-channels on both switches while they figure themselves out?

Thank you again for your help with this.

Martin

Hi,

I think when you enable spanning-tree on the second switch, the switches will start talking to each other to figure out which one is the main switch. This might cause a short period where traffic isn’t flowing through the port-channels.

However, because you’ve set the port-channel to be an edge port, it won’t get blocked even if it’s not the main path. This means the port-channel will keep forwarding traffic, so the servers will stay connected.

The switches will sort out their roles and adjust the port-channels, but this process shouldn’t block both port-channels at the same time. So, while there might be a brief moment of instability, it won’t stop the port-channels from working, and the servers will always have a connection to at least one switch.