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srroeder
Beginner

spanning tree question - blocked port

Hello everyone,  thanks in advance for any help you can give me.

I have a new site with a 6509 switch.  It is connected back to my main site by two P2P layer two trunks.  I have to trunk VLANs between the two sites for about six weeks until I get all of the equipment moved.  At that time I wil change them to layre 3 routed links.

When I connect one trunk no problem.  When I connect the second,  spanning tree blocks the first.

What is the best method to allow two layer two trunks to connect between the same two switches?

1 ACCEPTED SOLUTION

Accepted Solutions
mvsheik123
Rising star

Hi,

Did you think about port channeling (ether channel) both links? That might help you.

Thx

MS

View solution in original post

6 REPLIES 6
mvsheik123
Rising star

Hi,

Did you think about port channeling (ether channel) both links? That might help you.

Thx

MS

Thank you to everyone that replied.  I am going to attempt the etherchannel solution.

Aninda Chatterjee
Cisco Employee

Hello,

Spanning-tree is meant to avoid loops and with those two interfaces running between the two switches, one of them needs to be blocked to break the loop.

As MS correctly stated, you might want to think of port-channeling these two interfaces. This causes spanning-tree to look at the bundle as one logical link and the bundle interface would itself be forwarding, allowing traffic to go over both the individual interfaces based on your hashing algorithm.

Regards,

Aninda

Joseph W. Doherty
Hall of Fame Expert

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Posting

As the other poster has suggest, port-channel might be your best option (you can also use if for L3 when no longer have a need for the trunk).

Second best option (if doable), might be to vary cost of different VLANs on the two trunks.  With per-vlan-stp, you would block half your VLANs on each trunk.

Hi Joseph

Second best option (if doable), might be to vary cost of different VLANs on the two trunks.  With per-vlan-stp, you would block half your VLANs on each trunk.

That's actually a very good suggestion considering the scenario. It makes sense to try and load-balance across the two trunks if a port-channel is not doable.

Regards,

Aninda

Spanning Tree blocks will port one port because its creating loop in network.

if u want two ports should be used.  U can make ether channel and bind two ports in that channel because

  STP sees etherchannel as a single port

Jawad

Jawad