I'm practicing spanning-tree with two 2950 switches (Ver 12.1). I have 3 trunks and 3 vlans. I try to change the cost of the interface (for the 3 vlans) and only 2 vlans change the value after I apply the command. The command is "spanning-tree cost 1" in interface mode. Is there any explanation as why only two of the vlans change the cost? I hope to be clear on the scenario.
That's what I'm talking about.
spanning-tree vlan 3 port-priority 128
spanning-tree vlan 3 cost 19
spanning-tree cost 1
Obvoiusly, F0/7 has cost 19 for vlan 3 (grin). That's why it was in BLK state. When you configure port cost for a particular vlan it will override what you configured for all vlans.
spanning-tree vlan 3 port-priority 128 This doesn't help you to adjust things for downstream switch. (grin)
I know that you're familiar with SPT now. Have fun mate!!!
Hello Toshi, Francisco,
we can see that fas0/7 is the root port for vlan 1,2 but not for vlan 3.
the change in port cost has effects on path cost for vlan 1 and 2 but not for vlan3 that uses f0/5 as its root port with default cost 19.
We can guess that fas0/5 may be an access port in vlan3 and it has been selected as the root port for its lower port id 128.5 to be compared to 128.7 for fas0/7.
root bridge id is :
32770:0005.dccb.0580 for vlan2
32771:0005.dccb.0580 for vlan3
this clearly indicates the root bridge is the same device (the other switch).
probably fas0/7 doesn't carry vlan3 and it is a trunk but if so it shouldn't appear in sh spanning-tree vlan 3 output
you can post config and also sh ver of switches.
Hope to help