From: ccie_studying (ccie_studying@hotmail.com)
Date: Wed Feb 05 2003 - 01:19:06 GMT-3
I just read a little bit about this extended system ID.
For non-extended system ID, priority takes 2 bytes and then followed by MAC
address (6 bytes).
For extended system ID, priority only takes 4 bits, and then vlan ID (12
bits), and then followed by MAC address
So my guess is when you use extended system ID, you assign priority 0, which
added vlan number 2, it turns out your final priority is 2. If you change
your vlan number to other number, your final priority should be turn out as
your vlan number.
If you make it non-extended system ID, then your final priority should be 0.
I could not test it recently, would you test it and let me know?
----- Original Message -----
From: "Richard Hanks" <ccieingroup@hotmail.com>
To: "Pang Alan" <alanpang2002@hotmail.com>; <ccielab@groupstudy.com>
Sent: Monday, January 06, 2003 12:03 PM
Subject: Re: 3550 vlan priority problem
> 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#? > > > > _________________________________________________________________ > &b1z*:&f0J8K8m$W6G0e15&, Hotmail 6l%s!A=P2>&\: > http://zh-asiasms.mobile.msn.com > . > . .
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