RSTP and Trunk Links

Hi All,

New to Cambium gear. I have been reading and can see that trunk ports operate slightly different as opposed to in the Cisco sense. All VLANs are tagged and although you can set a native VLAN it only receives untagged frames it will not transmit them.

How does this work then when it comes to RSTP and BPDUs being sent between switches? and what VLAN are they sent on?

Thanks

Hi Adam,

Your understanding the behavior of cnmatrix trunk port is correct. However, the switch sends protocol packets such as RSTP, LLDP etc. untagged.

Thanks

Hi Tam,

Thanks for confirming so RSTP,LLDP and any other management traffic what VLAN will these be part of?

Would it be on VLAN 1 or for example would it be VLAN 99 (example if we set VLAN 99 to our Management VLAN). Would this essentially mean that whatever the management VLAN is set as that it would go over the trunk link untagged and in actual fact the trunk would send untagged frames?

Hi Adam,

The management traffic is tagged on a trunk port. I mentioned RSTP, LLDP as they are vlan independent.

If you require to have management traffic egressing untagged, port must be configured for hybrid mode. Please note that a port in hybrid mode is not automatically added to every VLANs present in the switch, and user must configure the hybrid port in selected VLANs. Please refer to this link for explanations of different port mode supported on cnmatrix :

Thanks

Thanks Tam

So for RSTP traffic for example BPDUs over a trunk if these are sent untagged then essentially this is the native vlan of the link? Is this vlan 1?

I am just wanting to clarify my understanding as we are looking at deploying Cambium across all our sites so I want to know exactly how it works

Thanks

Hi Adam, RSTP BPDU is sent untagged and will be received in the port’s native/pvid vlan. Please note that with RSTP, unlike PVRST and MSTP, all VLANs are part of the same STP domain.