Spanning tree root port

[evancurran14]

Gi1/1/1 Root  FWD  20000 128.49     P2p
Po1       Desg FWD  2000   128.2281 P2p

both are connected to the root bridge, which is a pair of 9500's. with each port connected to a different switch. G1/1/1 goes to core 1, with g1/1/2 going to core 2. trying to move them both to po1

Shouldn't the lowest cost be the root port?

I want to make the root port the port channel, so I can seamlessly add g1/1/1 to the port channel without spanning tree recalculating and taking the link down. 

[MHM Cisco World]

No friend not always'

If Port g1/1/1 receives bpdu from SW have lower mac then it will elect as root port.

The port cost use as tie breaker when both port receive bpdu from same SW

MHM

[Flavio Miranda]

@evancurran14 

We need more information. We need to see the topology at least.

[evancurran14]

they are both directly connected to the root bridge, which is a pair of 9500's

[Flavio Miranda]

On the switch , can you run

show spanning-tree interface Gi1/1/1

[evancurran14]

core side is po32 and g1/0/3

show spanning-tree vlan 6

Twe1/0/3 Desg FWD 20000  128.195 P2p

Po32        Desg FWD 20000  32.2120 P2p

I tried to lower the priority to see if that would have an effect on the far side

[MHM Cisco World]

check the mac address of 9500 you will see the bridge ID (mac + priorty) is different and then one connect to g1/1/1 have lowest 

[MHM Cisco World]

wait a min both port connect to both 9500 ?

if 9500 run stackwise virtual then 

""The spanning-tree domain treats the StackWise Virtual pair as one bridge node instead of two.""

and if one SW connect to other (stackwise virtual) with two link, one link will be root/dst and other will be BLK

MHM

[evancurran14]

is the same same switch... the root bridge. Both ports are connected to the root bridge, which has only one mac address.

ILLINI-DC-CORE#show spanning-tree vlan 6

VLAN0006
Spanning tree enabled protocol rstp
Root ID Priority 4102
Address 3473.2dd9.db20
This bridge is the root

[MHM Cisco World]

ILLINI-DC-CORE#show spanning-tree vlan 6 <<<- this STP from both C9500

VLAN0006
Spanning tree enabled protocol rstp
Root ID Priority 4102
Address 3473.2dd9.db20
This bridge is the root

And below for SW-X connect to both C9500 Stackwise ?

Gi1/1/1 Root  FWD  20000 128.49     P2p
Po1       Desg FWD  2000   128.2281 P2p 

if above correct then share the 
show portchannel summary in SW-X

MHM

[evancurran14]

This 9200 is connected to a pair of 9500's in a stackwise configuration. Sorry.

Show eterhcannel summary from edge switch


Number of channel-groups in use: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------------
1 Po1(SU) LACP Gi2/1/1(P)

[MHM Cisco World]

below for C9200 connect to two C9500, just confirm ?

Gi1/1/1 Root  FWD  20000 128.49     P2p
Po1       Desg FWD  2000   128.2281 P2p 

1 Po1(SU) LACP Gi2/1/1(P) <<- you use PO with one leg to connect to both C9500 ? 

is G1/1/1 port and PO1 connect to same C9500 SW ??

MHM

[MHM Cisco World]

1 Po1(SU) LACP Gi2/1/1(P) <<- you use PO with one leg to connect to both C9500 ? 

is G1/1/1 port and PO1 connect to same C9500 SW ??

[MHM Cisco World]

MHM

[evancurran14]

This really is very simple. 1 9200 connected to a 9500 stack. We connect g1/1/1 to core1 and 2/1/1 to core2. Used to be called a vss pair, and is now stackwise, maybe? But the 9500 pair is the spanning tree root. so virtually one switch plugged into one switch.

Why? Does it matter? But the answer is, we had one link in the past. G1/1/1 on the 9200 and we want to move to a portchannel. So the fiber guys ran a new pair and I created PO1 and started with he 2nd link with the idea being that we could change the spanning tree cost to prefer the port channel, then move the g1/1/1 into the portchannel without taking the network down in a hospital. I change the port cost on the edge, and the  root port did not move. I changed the priority on the core, and the spanning tree root port did not move. I actually had this scenario on s CCNP test 12 years ago

[MHM Cisco World]

PO1 in c9200 have one leg is connect to Core1 or Core2 ?
if it connect to Core1 then port must be BLK 
if it connect to Core2 and Core1/2 run StackWise virtual (one virtual SW) and PO and G1/1/1 is FWD State, we have problem 

the traffic from C9200 go to Core2 then vis SVL to Core1 and return to C9200 do you see it right ?

Sure Not, first stop to not make issue disable PO prevent storm 

also before you use PO in C9200 is G1/1/1 and G2/1/1 both are FWD state ?

MHM

[MHM Cisco World]

I hope idea is clear' 

Sorry I will enjoy with my family new year eve so I will be unavailable from now until 2/1/2025.

Happy new year friend 

Goodluck 

MHM