PVST Simulation Between SG350XG-24F and Catalyst 3560X - Load Balance?

[ksbolton1]

The SG350 is running MST in order to allow for multiple instances of STP while the Cat is running PVST+ (migrating all to MST is off the table for now). I'd like to connect these switches via multiple 1Gbps interfaces and in doing so, use each interface independently. That means neither interface being shut down due to STP. 

I've found that I can do this between two SG switches (MST and mapping vlans to instances) and two Cat switches (PVST+ where I made the interfaces access mode and placed them in separate vlans). I've read up on PVST simulation bit (Cisco PVST Simulation) and I've gotten the switches to play nice with each other but one of the SG ports always go to discarding mode. The Cat is the root bridge and that cannot be changed. 

I've tried to mess with port costs and priorities in order to try to get port 24 up and running but no luck. (The switches are connect Gi1/0/23 <-> Te1/0/23 and Gi1/0/24 <-> Te1/0/24. Is load balancing really possible when using PVST simulation between a MST and PVST+ region?

VLAN0006
  Spanning tree enabled protocol rstp
  Root ID    Priority    4102
             Address     0072.7838.6280
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4102   (priority 4096 sys-id-ext 6)
             Address     0072.7838.6280
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/23            Desg FWD 10        128.23   P2p
Gi1/0/24            Desg FWD 4         128.24   P2p

###### MST 2 Vlans Mapped: 6-13

Root ID        Priority    0
               Address     2c:ab:eb:23:84:c7
               This switch is the regional root
Interfaces
Name       State     Prio.Nbr   Cost      Sts  Role  PortFast  Type
--------   --------  --------   --------- ---- ----  --------  ----------
te1/0/23   enabled   128.23     30000     Frw  Mstr  No        P2P Bound (RSTP)
te1/0/24   enabled   0.24       20000     Dscr Boun  No        P2P Bound (RSTP)

[Reza Sharifi]

Never worked with SG series switches but can you put both ports on both switches in a Portchannel group? Doing that may bring up port 1/0/24 as you will have 2 physical interfaces in one logical Portchannel (no loop).

HTH

[ksbolton1]

Thank you for your reply. I'd like to use the individual physical ports separately and in doing so have two vlans use one of each of the links between the devices. The ultimate goal is to keep the traffic segmented while getting the full 1Gbps link capability for each vlan to use.

[Jaderson Pessoa]

@ksbolton1 Hello,

If you devices have two connection between them without port-channel, the STP will disable one port to prevent loop in your network, independetly if you are using MST or PVST+.  

I'm work with SG550xg and i have two running MST and my other catalyst running rapid-pvst, its works very well. 

Regards, 

[ksbolton1]

Thank you for your reply. I'm aware of how STP will work to prevent L2 loops. I'm trying to have two access links between two switches from different Cisco lines work without any of their ports shutting down. I know it's possible as long as STP instances are running per vlans or per MST instance but it seems a bit more complicated when crossing an MST-PVST+ boundary. That's what I'm trying to clarify here.

[paul driver]

Hello

---

@ksbolton1 wrote:

The SG350 is running MST in order to allow for multiple instances of STP while the Cat is running PVST+ (migrating all to MST is off the table for now). I'd like to connect these switches via multiple 1Gbps interfaces and in doing so, use each interface independently. That means neither interface being shut down due to STP. 

I've found that I can do this between two SG switches (MST and mapping vlans to instances) and two Cat switches (PVST+ where I made the interfaces access mode and placed them in separate vlans). I've read up on PVST simulation bit (Cisco PVST Simulation) and I've gotten the switches to play nice with each other but one of the SG ports always go to discarding mode. The Cat is the root bridge and that cannot be changed. 

I've tried to mess with port costs and priorities in order to try to get port 24 up and running but no luck. (The switches are connect Gi1/0/23 <-> Te1/0/23 and Gi1/0/24 <-> Te1/0/24. Is load balancing really possible when using PVST simulation between a MST and PVST+ region?

---

Looks like you not getting any PVST inconsistent states just a port being blocked to negate a loop. - However you say that these ports are in two different access vlans and not trunks correct?

Can you please confirm the BID priorities that are applied on the MST instances within the MST region switches and to the vlans non mst region switch(s).

[ksbolton1]

Hello and thank you.

In the past I've used two access port links but in this instance I did exactly as the link I included said, used trunk ports with native vlan 1. I also set the BID for the vlans and non-zero MST instances as shown in the link. I believe the only deviation from the instructions was slight in that I was unable to specify MST instance 0 on the SG so I used the spanning-tree priority command to set that value.

I'm not at the devices at the moment but as soon as as I get back I'll send the requested info.

[ksbolton1]

SG config:

spanning-tree mode mst
spanning-tree priority 12288
spanning-tree mst configuration
instance 1 vlan 2-5
instance 2 vlan 6-13
name TEST
exit
spanning-tree mst 1 priority 0
spanning-tree mst 2 priority 0
port jumbo-frame
vlan database
vlan 2-13
exit
!
interface TengigabitEthernet1/0/23
 spanning-tree link-type point-to-point
 spanning-tree mst 2 cost 30000
 switchport mode trunk
 macro description switch
 !next command is internal.
 macro auto smartport dynamic_type switch
!
interface TengigabitEthernet1/0/24
 spanning-tree link-type point-to-point
 spanning-tree mst 2 port-priority 0
 switchport mode trunk
 macro description switch
 !next command is internal.
 macro auto smartport dynamic_type switch
!

Catalyst config:

spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 8192
spanning-tree vlan 2-4094 priority 4096

interface GigabitEthernet1/0/23
 switchport mode trunk
 spanning-tree vlan 6-13 cost 10
!
interface GigabitEthernet1/0/24
 switchport mode trunk

!
interface Vlan1
 no ip address
 shutdown

[ksbolton1]

I've been tinkering with this but no dice. Can anyone offer additional guidance?

[ksbolton1 · Accepted solution]

In a stroke of luck, it seems the latest version of the SG350XG-24F firmware (2.5.0.79) brings PVST and Rapid PVST to the platform so if I upgrade, I should be able to avoid all this issue. I've already tested VLAN load balancing between an SG350 and a 2960-X and it works without issue.