Question about STP

[MGallardoH]

Dear sirs, What could be the best STP configuration for the attached scenary in the 460 switches?

I have two X460 linked with LAG and a non gestionable switch. I need a redundant path between HOSTC and HOSTA, and HOSTC and HOSTB. The prefer path between HOSTC and HOSTA must be through X460 A and the prefer path between HOSTC and HOSTA must be through X460 B. 

Any ideas?

Thanks in advance.

[Tomasz · Accepted solution]

Hi,

Is Spanning Tree a must or are you willing to consider other options as well?

I’m not sure of the preferred paths if we talk about just L2 forwarding, with STP you may have to play with bridge and port priorities to assure the link between X460-G2s is blocked. That’s the only link that makes sense so that host A is reached through X460 A and similar for B.

If you have few VLAN’s you could play MSTP but for the preferred paths you mention, I think quickly that both MSTP instances will need the same physical link to be blocked as redundant. If you had more VLANs and switches with meshy connections, RSTP is better IMHO (would be tough to manage bridge and port priorities for every bunch of VLANs to assure at least same number of VLANs using every single link, not talking about real traffic volume).

Is the need of preferred paths something of high priority?

Otherwise, if the setup is as shown, I would recommend to take a look at MLAG. Your non-EXOS switch would do static/dynamic LAG, X460-G2 would be logically peered on L2 for that device. Whatever path is taken from C to A/B, left or right, it will reach the destination. Of course, it would possibly require playing with load sharing algorithms on that downstream switch to assure nice load balancing or maybe even the ‘preferred path’ outcome you mentioned.

Hope that helps,

Tomasz