Re: Spanning tree PAGP question

Pricscilla

Long time since I've seen you. Did you go on a long long
vacation?




""Priscilla Oppenheimer""  wrote in
message 
news:200706280136.l5S1aHRC003648groupstudy.com...
> Bill Wharton wrote:
>>
>> How does spanning tree interact with a
PAGP/port-channel link?
>> I am
>> configuring a bunch of 6500 access switches all
conneted to a
>> 6500 core -
>> don't ask why they're all 6500's, too much money I
guess ;)
>>
>> They're all using hyrbid mode
>>
>> 1) Each switch connects to the core via a
port-channel link.
>> Now, does STP
>> treat a port-channel just as a regular port and
applies STP to
>> the channel
>> rather than the port?
>
> Yes, STP treats the channel as a single bridge port.
>
> What happens if one port in the channel
>> goes down?
>
> The channel has less bandwidth. I don't think anything
else happens.
>
>> Will STP converge causing a brief disconnect or it
woudln't
>> need to since
>> the other port will still be up?
>
> I don't think STP would do anything. Anyone else want
to comment? I'm a 
> bit
> rusty. 
>
>>
>> 2) The access switches are configured for
RAPID-PVST+ while the
>> core is
>> configured for PVST+ but it seems to be working.
Should I
>> change the core to
>> RAPID-PVST+ to ensure uniformity?
>
> You could change the cores to Rapid PVST+. It might be
a bit risky to make
> an extra change on a production network though...
>
>>
>> 3) The core has already been configured with 'set
spantree
>> priority 100' to
>> ensure it's the root switch at all times. Do I need
to really
>> change any
>> port priorities or costs on the access or core
switches? I mean
>> there's only
>> a single port-channel link between each access
switch and the
>> core hence
>> that port-channel itself would automatically be
calculated to
>> be the root
>> port on the access switches. Isn't it? I want to
keep
>> non-essential
>> configurations out.
>
> I would agree that there's no need to change port
priorities or costs on 
> the
> access switches. It's a bit hard to say for sure though
since I don't know
> your topology.
>
> I hope others answer too! I'm sort of testing the
waters after having been
> away from GS for a while. 
>
> Priscilla
>
>
>>
>>
>> Thank you
>>
>>
>> Log of core switch:
>> As you can see below, STP seems to be treating
port-channel 763
>> as a single
>> link
>>
>> ****************** show spantree active
******************
>>
>> VLAN 1
>> Spanning tree mode          PVST+
>> Spanning tree type          ieee
>> Spanning tree enabled
>>
>> Designated Root             00-d0-05-1d-68-00 (I
verified with
>> show module
>> and this MAC address belongs to the core)
>> Designated Root Priority    100
>> Designated Root Cost        0
>> Designated Root Port        1/0
>> Root Max Age   20 sec   Hello Time 2  sec   Forward
Delay 15 sec
>>
>> Bridge ID MAC ADDR          00-d0-05-1d-68-00
>> Bridge ID Priority          100
>> Bridge Max Age 20 sec   Hello Time 2  sec   Forward
Delay 15 sec
>>
>> Port                     Vlan Port-State    Cost   
  Prio
>> Portfast
>> Channel_id
>> ------------------------ ---- -------------
--------- ----
>> -------- ----------
>> 1/1,2/1                  1    forwarding           
3   32
>> disabled 763
>>  4/8                     1    forwarding           
4   32
>> disabled 0
>>  8/4                     1    forwarding           
4   32
>> enabled  0
>>  8/7                     1    forwarding          
19   32
>> enabled  0
>>
>>
>>
>>
>> Log of an access switch (other access switches look
very
>> similar)
>> As you can see below, the designated root has a MAC
address
>> belonging to the
>> core switch
>>
>> ****************** show spantree active
******************
>>
>> VLAN 1
>> Spanning tree mode          RAPID-PVST+
>> Spanning tree type          ieee
>> Spanning tree enabled
>>
>> Designated Root             00-d0-05-1d-68-00
>> Designated Root Priority    100
>> Designated Root Cost        3
>> Designated Root Port        1/1,2/1 (agPort 14/1)
>> Root Max Age   20 sec   Hello Time 2  sec   Forward
Delay 15 sec
>>
>> Bridge ID MAC ADDR          00-0f-35-e8-29-30
>> Bridge ID Priority          32769  (bridge
priority: 32768, sys
>> ID ext: 1)
>> Bridge Max Age 20 sec   Hello Time 2  sec   Forward
Delay 15 sec
>>
>> Port                     State         Role Cost   
 Prio Type
>> ------------------------ ------------- ----
-------- ----
>> --------------------
>> 1/1,2/1                  forwarding    ROOT       
3   32 P2P,
>> PEER(STP)
>>  7/3                     forwarding    DESG      
19   32
>> Shared, Edge
>>  7/5                     forwarding    DESG      
19   32 P2P,
>> Edge




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