Re: Etherchannel STP cost calculation

Naufal,

Can't read the distorted config but:

When you introduce a port channel to your STP infrastructure it calculates
the cost based on total bandwidth as you may expect. For instance if you
have 10, 100mbps links you should see a cost of 4 which represents 1Gbps. If
you know this general formula then considering the STP cost table you'll be
able to tell "where" on that table the custom cost is located.

For most of Port channels using the table you get a range like between 4 and
19. So the result could fall anywhere (depending on BW) between these two
extremes.

Last but not least, you might get some "irregular" results in Dynamips
although I've never analyzed them.

HTH
Kambiz Agahian

CCIE Instructor/Consultant
M.Eng Telecom, CCIE# 25341, CCSI# 33326, MCSE, MCSA

BTW, the config that you've sent is a bit distorted and I can't follow the
exact text.

On Sat, Aug 21, 2010 at 6:28 PM, Naufal Jamal <naufalccie_at_yahoo.in> wrote:

> Hi ,
> I am trying to find out how the cost for etherchannel STP is calculated .
> Please see the below output. Please help me understand how the cost has
> been
> calculated as 3 for PO4.
> Thank you,
> ddcxs01a-ddcxra#sh etherchannel 4 sumFlags: D - down P - bundled in
> port-channel I - stand-alone s - suspended H - Hot-standby
> (LACP
> only) R - Layer3 S - Layer2 U - in use f - failed
> to
> allocate aggregator
> M - not in use, minimum links not met u - unsuitable for
> bundling w - waiting to be aggregatedNumber of channel-groups in
> use:
> 19Number of aggregators: 19
> Group Port-channel Protocol
>
> Ports------+-------------+-----------+--------------------------------------
> -------4 Po4(SU) PAgP Gi2/13(P) Gi3/13(P) Gi4/13(P)
> Gi5/13(P)
>
> ddcxs01a-ddcxra#sh spanning-tree vlan 27
> VLAN0027 Spanning tree enabled protocol rstp Root ID Priority 27
> Address 0009.112f.b040 Cost 5 Port
> 1668 (Port-channel4) Hello Time 2 sec Max Age 20 sec
> Forward Delay 15 sec
> Bridge ID Priority 32795 (priority 32768 sys-id-ext 27)
> Address 000b.60f7.e180 Hello Time 2 sec Max Age 20 sec
> Forward Delay 15 sec Aging Time 300
> Interface Role Sts Cost Prio.Nbr Type---------------- ---- ---
> --------- -------- --------------------------------Po4 Root
> FWD 3
> 128.1668 P2p
>
>
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Received on Sun Aug 22 2010 - 13:38:42 ART