[c-nsp] Vlan 1 Root Bridge

[Carl Hester]

We have dual 6500 with SUP2s in Hybrid mode as our core.  I am working on 
converting the configuration from Hybrid to Native for our new cores.

We have our cores split to be the root bridge for alternating vlans.  Core1 
is the root for 5, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000.  And 
Core2 is root for 10, 110, 210, 310, 410, 510, 610, 710, 810, 910.

We set this configuration by "set spantree priority 0 <vlan ID>" on the 
cores and "set spantree priority 100 <vlan ID>" on the opposite core.  The 
rest of the switches in the network are using default priorities.



We set VLAN1 priority to 0 on Core1, but it does not show up in 'show 
spantree summary'.

<snip>
Core01> (enable) show spantree summary
Spanning tree mode: PVST+
MAC address reduction: disabled
Root switch for vlans: 5,100,200,300,400,500,600,700,800, 900,1000.
...
<snip>

The MAC address for VLAN1 Designated root is one of the Virtual MACs used by 
the SUP2 blade on Core1.  (00-08-7c-27-9f-33)

<snip>
Core01> (enable) show mod
...
Mod MAC-Address(es)                        Hw     Fw         Sw
--- -------------------------------------- ------ ---------- 
-----------------
1   00-06-d6-5a-76-3a to 00-06-d6-5a-76-3b 3.4    7.1(1)     7.6(1)
   00-06-d6-5a-76-38 to 00-06-d6-5a-76-39
   00-08-7c-27-9c-00 to 00-08-7c-27-9f-ff
...
<snip>

But the MAC address does not match the Bridge ID that VLAN1 is using on the 
switch.

<snip>
Core01> (enable) show spantree 1
VLAN 1
Spanning tree mode          PVST+
Spanning tree type          ieee
Spanning tree enabled

Designated Root             00-08-7c-27-9f-33
...
Bridge ID MAC ADDR          00-08-7c-27-9c-00
<snip>

It should be noticed that the Bridge ID MAC ADDR for each VLAN is by VLAN#.  
So Vlan1 is 00-08-7c-27-9c-00, Vlan2 is 00-08-7c-27-9c-01, Vlan3 is 
00-08-7c-27-9c-02, Vlan4 is 00-08-7c-27-9c-03.. etc.

Can anybody give me an explanation for why my designated root for VLAN1 isnt 
00-08-7c-27-9c-00?

Thanks in advance!