Allowing traffic on VLAN ID (PVID) mismatched links
When RPVST+ is running in the default configuration on a link where there is a VLAN ID mismatch, PVST blocks the link, causing traffic on the mismatched VLANs to be dropped. However, there can be instances where traffic passing between mismatched VLANs on a link is desirable. When enabled on the switch, the
ignore-pvid-inconsistency
command allows this behavior. That is, where the ports on both ends of a point-to-point link are untagged members of different VLANs, enabling
ignore-pvid-inconsistency
enables RPVST+ to process untagged RPVST+ BPDUs belonging to the peer’s untagged VLAN as if it was received on the current device’s untagged VLAN.
Syntax:
no spanning-tree ignore-pvid-inconsistency
Causes the switch to ignore per-VLAN ID inconsistencies when the ports on both ends of a point-to-point link are untagged members of different VLANs, thus allowing RPVST+ to run on the mismatched links. On a given switch, this affects all ports belonging to VLANs on which RPVST+ is enabled.
Default: Disabled
Switch “A” Port on VLAN X |
Switch “B” Peer port on VLAN Y |
RPVST+ behavior with ignore-pvid-inconsistency enabled |
---|---|---|
Untagged on VLAN 10 |
Untagged on VLAN 10 |
Forward |
Untagged on VLAN 10 |
Untagged on VLAN 20 |
Forward1,1 |
Untagged on VLAN X |
Tagged on VLAN X |
Drop |
Untagged on VLAN X |
Tagged on VLAN Y |
Drop (traffic from both VLANs) |
Tagged on VLAN X |
Tagged on VLAN X |
Forward11 |
Tagged on VLAN X |
Tagged on VLAN Y |
Drop (traffic from both VLANs) |
Forwarding state applies if the link has not been blocked by RPVST+ as a redundant link.
The
no spanning-tree ignore-pvid-inconsistency
command is ineffective when there is a PVID inconsistency between a VLAN1 and any non-VLAN1 member because VLAN1 uses IEEE BPDUs to form a spanning tree topology.