From: ccieingroup@hotmail.com
Date: Fri Jan 03 2003 - 13:55:30 GMT-3
Hi Prashanth,
Thanks for your reply. I have read the link you gave me. This example is the
same as what I read in "Catalyst 3550 Multilayer Switch Software
configuration Guide.pdf" Chapter 10-26 Configuring VLANs (Load Sharing Using
STP) and Chapter 14-15 configuring STP( Configuring the port priority)."
I just wonder why in this example, cisco didn't mention which switch is the
root switch though it mentioned where to put the commands. So let's assume
Switch A(or switch 1) is the root switch for all vlans, there are two parallel
trunk connections between the switch A(switch 1) and switch B(or said switch 2
in the real cisco example). Now I want to use the "spanning-tree vlan ...
port-priority ..." commands to control which port on switch B to be in the
block state. Where should I put the command "spanning-tree vlan ...
port-priority ...", on switch A or on switch B, if A is root for all Vlans and
all A ports are in forwarding state. Cisco never mentioned in the "3550
configuration guide" that this command should be put on the upstream switch to
influence downstream or put on the downstream directly.
> Switch A (Root Bridge for all vlans)
> 0/1| |0/2
> 1/1| |1/2
> Switch B.
I also refer to the "CCIE Professional Development Cisco LAN Switching" Page
249: Port/VLAN Priority- "set spantree portvlanpri" can be used to load
balance between back-to-back switches. This technique allows network
administrators to modify port ID values(Port ID=Port priority + Port number)
on upstream switches to influence forwarding and blocking decisions on
neighboring downstream switches."
Thanks,
Richard
----- Original Message -----
Wrom: DREXCAXZOWCO
To: Richard Hanks ; ccielab@groupstudy.com
Sent: Friday, January 03, 2003 2:13 AM
Subject: Re: One question about 3550 Port Priority?
Switch B
if Switch A is the root bridge for all your VLANs
(all ports in forwarding)
and the only way to load-balance is by playing with
the port priority on the downstream switch (B)
say if you have 4 VLANS and Switch A is the Root for
all the 4.... by default one of the trunk ports on
Switch B will be in blocking state...
you can modify the port priority on one one trunk port
for two vlans to be in forwarding state and two in
blocking state....similarly on the other so that each
trunk port carries traffic from two VLANs... when one
fails....one trunk carries all the traffic...
http://www.cisco.com/en/US/products/hw/switches/ps628/products_configuratio
n_guide_chapter09186a008007e8c7.html#xtocid45
-prashanth-
--- Richard Hanks <ccieingroup@hotmail.com> wrote:
> Hi Friends,
>
> I have a question here about the 3550 Port Priority.
> Please refer to the
>
> "Catalyst 3550 Multilayer Switch Software
> configuration Guide.pdf" Chapter
> 10-26 Configuring VLANs (Load Sharing Using STP) and
> Chapter 14-15 configuring
> STP( Configuring the port priority).
>
> My question is if two 3550 connected by two trunk
> links like this one.
>
> Switch A (Root Bridge)
> 0/1| |0/2
> 1/1| |1/2
> Switch B.
>
> I want to use the "spanning-tree vlan 20
> port-priority ..." to make the Switch
> B's 1/1 in forwarding state for vlan 20 but 1/2 in
> the block state. Where
> should I put the "spanning-tree vlan ..
> port-priority" command on? I mean
> whether on Switch A's port 0/1 and 0/2 or Switch B's
> 1/1 and 1/2. I mean
> whether the upstream switch or downstream switch
> directly.
>
> I also refer to the "CCIE Professional Development
> Cisco LAN Switching" Page
> 249: Port/VLAN Priority- "set spantree portvlanpri"
> can be used to load
> balance between back-to-back switches. This
> technique allows network
> administrators to modify port ID values(Port ID=Port
> priority + Port number)
> on upstream switches to influence forwarding and
> blocking decisions on
> neighboring downstream switches."
>
> But I can't find any such description in the 3550
> configuration guide. From
> the example of page 10-26. Though it mentioned where
> to put the commands on,
> but it didn't mention which switch is the root.
>
> Appreciate for any help.
> Rgds,
> Richard
> .
>
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