Adding port-channels in existing STP topology

[aajvandewiel]

Hello,

current topology is build from 4 6500 switches connected in a ring topology. Using Portchannel (2x 10Gbit) links to connect left side top and bottom 6500's (DC1), 10 Gbit link to connect right side 6500's (DC2)

Inbetween a 1 Gbit link is used to connect top 6500's (DC1-DC2) and the same for bottom 6500's (DC1-DC2).

Path costs are 5 and 6 so the T5/4 from bottom right is blocking.

Bandwidth demands are increasing, so thinking about adding extra 1 Gbit links to the existing ones and create etherchannels.

Path costs here are 4 and 5, so T5/4 from bottom right is still blocking, but when the bottom 2 Gbit port-channel is loosing one 1 Gbit link the path costs of both directions become equal. So I am worried that STP will not reconverge and leave me with a congested 1 Gbit link.

I cannot test this setup in a lab, are there any options to help STP to reconverge here?

Appreciate your efforts,

Arthur

[aajvandewiel]

Ok, just found out : if two paths are equal costs, the port with the lowest port ID (prio and port number) will win. So it is a matter of trying to arrange a lowest port ID on the blocking path incase the primary path will loose a 1 Gbit link inside the port-channel.

Lets find out the port numbers for portchannels.