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STP blocking Trunk between 5308's

reggieboy
Occasional Visitor

STP blocking Trunk between 5308's

HI,

Probably a really easy answer just cant figure it out. I have 2x 5308's configured with a 2xlink trk between them. I am currently adding redundant paths for all my edge switches and everytime I connect one of the switches the trunk on the corresponding 5308 goes into blocking state.

I have changed the priority of the trk to 4(64) and this still doesnt work. I havent tried disabling STP on the trunk. is that an option?

I feel like such a noob..
5 REPLIES
Ralph Bean_2
Trusted Contributor

Re: STP blocking Trunk between 5308's

Reggieboy -

It is tricky to have a discussion like this without a network map and knowledge of which device is root, but based on the information that you made available it appears that you should modify the port cost, not the port priority

Ralph
Matt Hobbs
Honored Contributor

Re: STP blocking Trunk between 5308's

Reggieboy. Most likely you have your spanning-tree priority left to the default setting of 8 for all switches at the moment.

The easiset thing to do is set your 5300's to a higher spanning-tree priority.

5300-1(config)#spanning-tree pri 1

and then on the other 5300

5300-2(config)#spanning-tree pri 2

Otherwise what will happen when all switches have the same priority, the switch with the lowest mac-address will become the root switch, which is why the trunk link is being blocked.
reggieboy
Occasional Visitor

Re: STP blocking Trunk between 5308's

I will look at port cost. I already have switch 1 as pri 1 and the second is the default prioity. this happens when I plug my switches into core 2 which blocks core 2.

I have attached configs and a NW diagram so you can see what I am talking about.

hope you can read it.

Cheers,

Trev (reggieboy)
Matt Hobbs
Honored Contributor

Re: STP blocking Trunk between 5308's

The edge switches have spanning-tree enable too right?

If you could share the config of those switches it may help.

Also, while they're all connected and you can see the problem, capture the 'show span' on each switch as well.

But really it should be that simple. Set the spanning-tree priority on your core switches, enable spanning-tree on the rest and it should choose to forward over the trunk link and block one of the other links instead. If not, show span will give us some more clues as to what's happening.
reggieboy
Occasional Visitor

Re: STP blocking Trunk between 5308's

yes they do. when I do a show span on the 5308's when connected it shows the root port as being one of the ports that connects to the edge switches in question. If I connect other edge switches, they block correctly - at thier end and the trunk stays up. It just seems to be these two switches.

Anyway, rebuilding the config on both so I will see how that goes.

Thanks for your help.