Setting the Basis Bridge
It’s affectionate of acceptable that the Core about-face is the basis arch by absence because that’s right
where I’d about accept to set the root. But aloof for fun, let’s change it. Here’s how you can
do that:
S1#config t
S1(config)#spanning-tree vlan 1 antecedence ?
<0-61440> arch antecedence in increments of 4096
S1(config)#spanning-tree vlan 1 antecedence 16384
S1(config)#do appearance spanning-tree
VLAN0001
Spanning timberline enabled agreement ieee
Root ID Antecedence 16385
Address 001b.2b55.7500
This arch is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Antecedence 16385 (priority 16384 sys-id-ext 1)
Address 001b.2b55.7500
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- -----------
Fa0/3 Desg FWD 100 128.3 Edge Shr
Fa0/4 Desg FWD 19 128.4 Edge P2p
Fa0/8 Desg FWD 19 128.8 P2p
Po1 Desg FWD 12 128.56 P2p
By blurred the S1 antecedence to 16384, the S1 about-face anon became the basis bridge.
You can set your priorities all the way from 0 to 61440. Zero (0) agency that the about-face will
always be the basis bridge, and 61440 agency the about-face will never be a root.
There’s one aftermost command I appetite to acquaint you about; if you appetite to skip all this verification
and agreement of the basis arch stuff—and no, you don’t get to skip all that if you want
to canyon the Cisco exams—here’s a simple command you can run on a about-face to set it as a root
bridge:
S1(config)#spanning-tree vlan 1 basis ?
primary Configure this about-face as primary basis for this spanning tree
secondary Configure about-face as accessory root
S1(config)#spanning-tree vlan 1 basis primary
Understand that this does not override a low-priority switch; this command would work
for you alone if all your switches had the aforementioned priority, or higher, set.