HP Edge Switches connected to Cisco Distribution Switches

[aali]

Attached is a very useful HP document explaining line by line how to connect HP A Series switches to Cisco Distribution Switches after HP of support STP Mode PVST.

I understand everything except why to tweak Port cost for VLAN Load Balancing.

If HP is connecting to one Cisco Distribution Switch then I can understand that we will need to adjust port cost on HP Switches to decide which VLANs will be active on link 1 and backup VLANs on Link1 and vice versa on Link 2.  But if HP switch is connected to two Cisco Distribution Switches and Cisco Switches are configured with VLANs priorities then I don't think that chaning a port cost will be a right way to do it.  The Cisco Distribution switches will decide regarding active/Standby paths based on VLANs priorities.

I will be implementing a same scenerio in a real production network and the only difference in my configuration will be that I will have two A5830-48 port switches in an IRF will be connected to two Cisco 6513 distribution switches.  I will be configuring one port from each A5830 in  20Gb LACP connected to Cisco Disrtibtution 6513A and the other 20Gb LACP connected to Cisco Distribution 6513B.  The VLANs priorites will be higher so they will not become root bridges and Cisco Switches will decide the Active/Standby Paths on both links based on VLANs priroities to implement VLANs load balancing.

[Michael A. McKenney]

It is based on STP (Spanning Tree Protocol).  You have two VLANs that form a loop, if you did not set one as failover.  You can't have a loop on a switch.    If you use IRF, the switches become one massive switch.  With VLANs on IRF, you can't have multiple active paths between VLANs.