From: stefan vogt (stefan-uwe_vogt@web.de)
Date: Sat Jan 04 2003 - 15:51:26 GMT-3
Hello Prashanth, Hello Richard,
Interesting stuff. I think the behavior should be adhere to the standard and be platform independent.
Acording "Cisco LAN Switching" (Clark), page 228:
---snip---
First notice that the non-Root Bridge must implement loadbalancing. Recall that all ports on the Root Bridge become Designated Ports and enter the Forwarding state. Therefore the non-Rot Bridge must select a single Root Port and place the other port in a Blocking state. ...
Second, it is the received values that are being used here. Cat-A is not evaluating its own BID and Port ID, it is looking at the values contained in the BPDUs being received from Cat-B.
---snap---
Note: In the scenario used here Cat-A is the non-Root Bridge, Cat-B is the Root Bridge.
For my understanding that means that we have to adjust the port priority on the Root Bridge, the non-Root Bridge then decides which port to block depending on the received BPDUs.
Does this match your findings?
-Stefan
"Richard Hanks" <ccieingroup@hotmail.com> schrieb am 04.01.03 18:15:43:
> Hello ,
> You said you ever test this command on Cat 5000 switch and the "set spantree
> portvlanpri" command should be put on the downstream switch. I also asked this
> question to Chuck Church and got this helpful link about this issue. The
> detailed description are different from your test result. After you read it,
> may we talk about this issue further. Now I just wonder that whether on 3550,
> the "spanning-tree vlan .. port-pri .."comannd is the same as on the 5000's
> "set spantree portvlanpri command", which is definitely should be put on the
> upstream switch to influence the downstream switch's decision about which port
> should be blocked and which one should be in forwarding.
>
> "http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080
> 0ae96a.shtml"
>
>
> Thanks,
> Richard
> ----- Original Message -----
> From: Richard Hanks
> To: Prashanth
> Sent: Friday, January 03, 2003 9:48 PM
> Subject: Re: One question about 3550 Port Priority?
>
>
> Hi Prashanth,
>
> Thank you very much for your reply!
>
> Rgds,
> Richard
> ----- Original Message -----
> From: Prashanth
> To: ccieingroup@hotmail.com ; ccielab@groupstudy.com
> Sent: Friday, January 03, 2003 3:35 PM
> Subject: Re: One question about 3550 Port Priority?
>
>
> Richard,
>
> >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.
>
> the commands go on the trunk port of the downstream
> switch (non-root or designated bridge)
>
> I have not gone through the 3550 doc myself, I have
> tried this on the 29xx/35xx XL/Cat 5k switches and it
> works ... if it does not mention about the root switch
> you might want to Submit a feedback to Cisco and see
> what is their reply..
>
> -prashanth-
>
>
>
>
>
> --- ccieingroup@hotmail.com wrote:
> > 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_configurat
> io
> > 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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