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04-17-2019 07:13 AM - edited 04-17-2019 07:16 AM
04-17-2019 07:13 AM - edited 04-17-2019 07:16 AM
MSTP: Port Cost set low, but still Discarding
Hello!
I have a couple of S5120-28C-PWR-EI switches here.
They are connected to each other with 2 Ethernet cables.
Im trying to establish an evaluation setup for MSTP here.
Everything is working so far. Except that port cost is not respected in any way.
The same port is always FORWARDING, no matter if i put very high port cost on this one, and very low port cost on the other one.
----[Port19(GigabitEthernet1/0/19)][FORWARDING]---- Port Role :Master Port Port Priority :128 Port Cost(Legacy) :Config=201 / Active=201 Desg. Bridge/Port :0.3ce5-a637-ebca / 128.19 Num of Vlans Mapped :2 Port Times :RemHops 20 ----[Port20(GigabitEthernet1/0/20)][DISCARDING]---- Port Role :Alternate Port Port Priority :128 Port Cost(Legacy) :Config=8 / Active=8 Desg. Bridge/Port :0.3ce5-a637-ebca / 128.20 Num of Vlans Mapped :2 Port Times :RemHops 20
[SW-VIE-IT29-GigabitEthernet1/0/20]dis this # interface GigabitEthernet1/0/20 description "STPTEST1" port link-type trunk undo port trunk permit vlan 1 port trunk permit vlan 77 to 78 port trunk pvid vlan 79 poe enable stp instance 1 cost 8 #
How is that possible?
Regards,
ND
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04-17-2019 05:18 PM
04-17-2019 05:18 PM
Re: MSTP: Port Cost set low, but still Discarding
Hi
It is observed that when you connect two 5120 switches using two cable the port with least port number is preferred than that of the port priority .
In your case the port 19 would always be the root port . You can try connecting another cable on 21 which has higher port number and shut the 19 port and observe . As per my theory the 20th port would be the root port and would be in forwarding state .
Please raise a case with HPE TAC to verify if it is a firmware issue .
I am an HPE Employee
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04-18-2019 11:54 AM
04-18-2019 11:54 AM
Re: MSTP: Port Cost set low, but still Discarding
So, are you trying to say "cost" and "priority" parameters are useless, because those H3C switches are taking the port number with the lowest value as those with lowest cost?
Wow, that would be a horrific bug.
We don't have any lower ports available on those coreswitches, they are all filled up already.
We just had a troubleshooting session with all kind of combinations of priority, cost and stp standard settings.
That one port is always discarding. Except if you pull the network cable from the other one. Then it changes to FORWARDING.
There seems to be really no way to accomplish this.
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04-21-2019 08:09 PM
04-21-2019 08:09 PM
Re: MSTP: Port Cost set low, but still Discarding
Hi
I noticed the change of cost affects the STP also the priority on the root switch affects the election .
Last time I was checking on the non root switch . You can also try modifying the STP parameters on the root switch .
I am an HPE Employee