From: Richard Hanks (ccieingroup@hotmail.com)
Date: Mon Jan 06 2003 - 14:03:34 GMT-3
Hi alan,
Please refer to the 3550 configuration guide page 349.
"Configuring the Switch Priority of a VLAN
You can configure the switch priority and make it more likely that the switch
will be chosen as the root
switch.
Note Exercise care when using this command. For most situations, we recommend
that you use the
spanning-tree vlan vlan-id root primary and the spanning-tree vlan vlan-id
root secondary global
configuration commands to modify the switch priority.
Beginning in privileged EXEC mode, follow these steps to configure the switch
priority of a VLAN:
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 spanning-tree vlan vlan-id priority priority Configure the switch
priority of a VLAN.
!E For vlan-id, the range is 1 to 4094. Do not enter leading
zeros.
!E For priority, the range is 0 to 61440 in increments of
4096; the default is 32768. The lower the number, the
more likely the switch will be chosen as the root switch.
Valid priority values are 4096, 8192, 12288, 16384,
20480, 24576, 28672, 32768, 36864, 40960, 45056,
49152, 53248, 57344, and 61440. All other values are
rejected.
Step 3 end Return to privileged EXEC mode.
So you see, only these 15 values are valid, other will be rejected.
Ricard.
----- Original Message -----
From: Pang Alan
To: ccielab@groupstudy.com
Sent: Friday, December 27, 2002 9:45 PM
Subject: 3550 vlan priority problem
Hi Group,
When I set the vlan priority to 0, the priority changes to 2. If I view the
priority from another switch, the priority is also 2.
The following is the related config and show commands. I see the line
Bridge ID Priority 2 (priority 0 sys-id-ext 2)
It just like the extended system id is added to the priority.
However, you can see that I have no extended vlans.
The questions:
1.Why the priority is different from the config and how to correct it?
2.How is the sys-id-ext derived?
Thank you very much.
Regards,
Alan
c3550#sh run
!
hostname c3550
!
enable secret level 14 5 $1$dpBd$QoyMzvsI6NkcSmji.tUO31
enable secret 5 $1$1J29$9XO/XWKVgjs3T11T0llap0
!
!
spanning-tree extend system-id
spanning-tree vlan 2 priority 0
!
!
c3550#sh span root
Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0001 32768 0004.c13b.0100 19 2 20 15 Fa0/10
VLAN0002 2 0009.b7e1.6b80 0 2 20 15
VLAN0003 32771 0009.b7e1.6b80 0 2 20 15
VLAN0068 32768 0004.c13b.0102 19 2 20 15 Fa0/10
VLAN0814 32768 0004.c13b.0103 19 2 20 15 Fa0/10
c3550#sh span vlan 2
VLAN0002
Spanning tree enabled protocol ieee
Root ID Priority 2
Address 0009.b7e1.6b80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 2 (priority 0 sys-id-ext 2)
Address 0009.b7e1.6b80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port
ID
Name Prio.Nbr Cost Sts Cost Bridge ID
Prio.Nbr
---------------- -------- --------- --- --------- --------------------
--------
Fa0/10 128.10 19 FWD 0 2 0009.b7e1.6b80
128.10
Try to view the priority from another switch.
cat3500#sh span vlan 2
Spanning tree 2 is executing the IEEE compatible Spanning Tree protocol
Bridge Identifier has priority 20480, address 0004.c13b.0101
Configured hello time 2, max age 20, forward delay 15
Current root has priority 2, address 0009.b7e1.6b80
Root port is 23, cost of root path is 19
Topology change flag not set, detected flag not set, changes 6
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Interface Fa0/10 (port 23) in Spanning tree 2 is FORWARDING
Port path cost 19, Port priority 127
Designated root has priority 2, address 0009.b7e1.6b80
Designated bridge has priority 2, address 0009.b7e1.6b80
Designated port is 10, path cost 0
Timers: message age 1, forward delay 0, hold 0
BPDU: sent 19435, received 666
cat3500#?
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