Scaling the Spanning Tree Protocol
195
travel over only the one link. However, by changing the port priority for a
specific group of VLANs, you can distribute the VLANs across the two links.
To change the priority of STP for a certain VLAN or group of VLANs, use
the set spantree portvlanpri command:
Todd5000> (enable) set spantree portvlanpri ?
Usage: set spantree portvlanpri <mod_num/port_num>
<priority> [vlans] (priority = 0..63)
Todd5000> (enable)
The priority can be set for each VLAN from 0 to 63. In the following
example, we'll set port 1/1 to forward only VLANs 1 and 2 and port 1/2 to
forward VLANs 3 and 4:
Todd5000> (enable) set spantree portvlanpri 1/1 16 1-2
Port 1/1 vlans 1-2 using portpri 16.
Port 1/1 vlans 3-1004 using portpri 20.
Port 1/1 vlans 1005 using portpri 4.
Todd5000> (enable) set spantree portvlanpri 1/2 16 3-4
Port 1/2 vlans 1-2,5-1004 using portpri 32.
Port 1/2 vlans 3-4 using portpri 16.
Port 1/2 vlans 1005 using portpri 4.
Todd5000> (enable)
The switch output above displays the VLAN priority information. We set
both VLAN port priorities to 16. Notice that for VLANs 14, the priority is
16. However, on port 1/1, all the other VLANs are listed as having a port pri-
ority of 20 because that is what we set the port priority to earlier in this chap-
ter. On port 1/2, the switch thinks all the other ports have a port priority of
32, except for VLAN 1005, which becomes a default priority of 4.
You can view the changes by using the show spantree slot/port com-
mand, as shown below:
Todd5000> (enable) sh spantree 1/1
Port Vlan Port-State Cost Priority Fast-Start
--------- ---- ------------- ----- -------- ----------
1/1 1 forwarding 10 16 disabled
1/1 2 forwarding 10 16 disabled
1/1 3 forwarding 10 20 disabled
1/1 4 forwarding 10 20 disabled
1/1 1003 not-connected 10 20 disabled
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com