Spanning tree: To make 3550-1 as the vtp server as well as the root bridge

by Cyrus Lok on Thursday, May 13, 2010 at 10:16pm

3550-1(config)#spanning-tree vlan 1 priority ?
<0-61440> bridge priority in increments of 4096

3550-1(config)#spanning-tree vlan 1 priority 5096
% Bridge Priority must be in increments of 4096.
% Allowed values are:
0 4096 8192 12288 16384 20480 24576 28672
32768 36864 40960 45056 49152 53248 57344 61440
3550-1(config)#spanning-tree vlan 1 priority 4096

I have made a typo unintentionally, fortunately IOS has advised…

3550-1#sh spanning-tree vlan 1

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 000b.be08.f480
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 000b.be08.f480
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p

Undisputed root bridge now.. great… btw the BID is priority + vlan id

3550-2 will be the secondary root if 3550-1 is down for some reason…

3550-2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
3550-2(config)#spann
3550-2(config)#spanning-tree vlan 1 pri
3550-2(config)#spanning-tree vlan 1 priority 8192
3550-2(config)#end
3550-2#sh spa
*Mar 1 00:09:05.363: %SYS-5-CONFIG_I: Configured from console by console
3550-2#sh spann
3550-2#sh spanning-tree vlan 1

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 000b.be08.f480
Cost 38
Port 2 (FastEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 8193 (priority 8192 sys-id-ext 1)
Address 000c.85e5.5380
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Fa0/1 Altn BLK 19 128.1 P2p
Fa0/2 Root FWD 19 128.2 P2p

The spanning tree is based on per vlan basis, so the BID is valid for vlan 1 only.

2950 is just a normal switch so… it is not suitable to be root bridge, because MLS will be acting as distributor whereas 2950 is acting as a switch in the access layer.

There’s one problem, fa0/1 is blocked… instead of designated, I will have to adjust the cost later.