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? What happens if one port in the
channel goes down?
Will STP converge causing a brief disconnect or it woudln't
need to since
the other port will still be up?
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?
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.
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
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7
&i=122907&t=122907
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