From: Anthony Pace (anthonypace@xxxxxxxxxxx)
Date: Thu Jun 20 2002 - 03:22:00 GMT-3
That makes sense.
portvlancost is for trunks to set cost per vlan on a port
portcost is for a port on a single vlan
Is the portvlanpri and portpri a more signifigant than the cost?
Anthony Pace
On Wed, 19 Jun 2002 14:56:50 -0700 (PDT), "Chris Hugo"
<chrishugo@yahoo.com> said:
>
> Hi Anthony,
>
> I'll answer a couple of questions. There are a lot of gurus on this mailing l
ist that will be happy enough to fill in the rest :)
>
>
> Configuring Port Cost
> You can configure the port cost of switch ports. Ports with lower port costs
are more likely to be chosen to forward frames. Assign lower
>
> numbers to ports attached to faster media (such as full duplex) and higher nu
mbers to ports attached to slower media.The possible range
>
> is 1 to 65535. The default differs for different media. Path cost is typicall
y 1000 w LAN speed in megabits per second.
>
> Key Concept: This will set a port cost in General to the port itself for and
all vlans on that port.
>
> Configuring Port-VLAN Cost
> You can configure the port cost for a port on a per-VLAN basis. Ports with lo
wer port-VLAN costs are more likely to be chosen to forward
>
> frames. You should assign lower numbers to ports attached to faster media (su
ch as full duplex) and higher numbers to ports attached to
>
> slower media. The possible range is 1 to 65535. The default differs for diffe
rent media.
>
> Key Concept: This is usually used when you have a two or more uplinks betwee
n two switches and you want traffic to flow over a
>
> specific port rather than another port on your switch. By default spanning tr
ee will allow only one port to be in the
>
> forwarding state. Now let's say you have 2 uplinks between a switch. You want
all traffic for VLANS 6-7 to be switched over port 1
>
> and you want VLANs 8-9 to use port 2. You can set a lower cost on port 1 for
VLANs 6-7. You would do the same on
>
> port 2 for VLANs 8-9. Now instead of using one port only you can now utilize
both ports for traffic.
>
> Now your question might be what if port 1 goes out? Will my VLAN traffic for
VLANs 6-7 still be switched over port 2? The answer is
>
> yes because of the General port cost that is STILL assigned on port 2. It act
s like a catch-all for all other VLAN traffic. Since
>
> port 1 is down there is no other favored (lower cost) port available and will
switch the traffic over port 2. Vice-Versa if port 2 goes out.
>
> Another note: You cannot set the Port-VLAN Cost parameter higher than the Gen
eric port cost assigned on a particular interface.
>
> http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_5_5/cnfg_gd/sp
antree.htm#xtocid1496212 is good link.
>
> I took a couple of excerpts out of there.
>
> hth,
>
> chris hugo
>
> Anthony Pace <anthonypace@fastmail.fm> wrote: Chris,
>
> You sound like you ar definitly "in the know". Can you verify the
> following:
>
> I think the SET SPANTREE ROOT is just a "canned" way of pushing a
> fairly low prioriy into the switch. I don't think it is as effective a
> setting the priority for a VLAN manually because when you do it
> manually you can make it really low (100 or 1 or whatever). The ROOT
> GUARD funtion can also be used to enforce the root position of the
> switch.
>
> I have another question: what is the difference between these two
> commands? I know they effect the port priority:
>
> set portvlancost
> set port cost
>
> THis is my understanding of how the other commands work and if someone
> can confirm/correct me that would be GREAT!
>
> 1)On a router doing bridging we set the priority for the "BRIDGE" in
> global configuration which determines our stanind in the spanning tree
> root election.
>
> 2)On a router doing bridging we set the priority for the "PORT" in the
> interface configuration. This determines this interfaces standing in
> the decision of which port/interface on the ROUTER will be the optimal
> path to the ROOT (in case we are not the root and there are redundant
> paths and we need to BLOCK one)
>
> 3)On a CAT5 switch we use SET SPANTREE ROOT or SET SPANTREE PRIORITY or
> SET SPANTREE ROOT which determines our stanind in the spanning tree
> root election.
>
> 4)On a CAT5 switch we use "set portvlancost" or "set port cost". This
> determines this interfaces standing in the decision of which
> port/interface on the ROUTER will be the optimal path to the ROOT (in
> case we are not the root and there are redundant paths and we need to
> BLOCK one)
>
>
> Is this right or wrong?
>
> Anthony Pace
>
>
>
>
>
>
> --
> Anthony Pace
> anthonypace@fastmail.fm
>
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