Should i change STp cost on fibre trunks?

[cdove]

We have a 5412ZL with a 2 fibre trunk to our existing network. these connect to a 2800 switch and then uplinks at 100mb to our old Netgear switches. These then uplink again then terminate in the comms room.
I am just having 2 more fibres installed directly from the comms room to the new server room where the 5412zl lives.
My question is if i connect both fibre trunks to the 5412zl, STP should block one but how can i ensure it will block the older trunk which i want just as failover?

TIA

 

[cajuntank]

Are the trunks the same speed?
Also if I remember correctly, the 5400 don't supprt STP they supprt MSTP which is backward compatible with STP.

 

[cdove]

The trunks both consist of 2 x 1gb Fibre. When i plug both in the network grinds to a halt. This is why i was wondering if i need to change the default value of the fail over link?

TIA

 

[LawnBoy]

Ordinarily, STP does not manage trunked ports (at least, not on the 53xx, 41xx, and 25xx series). When you activate both trunks at once, you are creating a topo loop and ARP-storming your network.

"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[LawnBoy]

Ya learn sumthin new every day...

Turns out MSTP will work in conjunction with trunks. The 5400zl manual talks about how trunks appear in the STP list as a single entity and therefore can be adjusted as if they were a single port.

So, in my mind, MSTP should manage the redundant trunks since it treats each one as if it were a single port. Why your network is flooding is mysterious.

I would try changing the cost of the reduntant link to, say, 10 times the cost of the primary link and see what you get. If the network stalls again I would say that MSTP is not managing the redundant trunks as advertised.


"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[cdove]

Would you happen to know how to change the cost? Looking at the info i need to create the trunk again specifying the path priority.

TIA

 

[LawnBoy]

Not offhand, but it's in the manual.


"We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth." - Sherlock Holmes

 

[BAsh12]

Do not change the cost. Very bad practice.

MSTP is RSTP but you carry multiple VLANS in a single instance.

First rule, make a root switch, this should be the switch that can see the best view of the network.

Do not forget to set the priority for both MST instance 1 and 0.

I also suspect you have not included all you r VLANs in te instance, you must, if not, the VLAN not included will definately cause a loop in the network.

MSTP is not too hard to configure, remember, if you ever add a VLAN, you need to include it in the instance.

There are some clever things you can do with it as well.

EG, you can have two switches at the core, set the left as root for odd VLANs, make the second switch for even vlans. Make each switch backup root for each other, now you have a form of load bakancing, better still, the network will re-converge in lilliseconds rather than seconds.

Half you VLANs will traverse one link, the other half up the other. You use all that you paid for.