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
RPVST+ behavior with ignore-pvid-inconsistency enabled
| 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[a] |
| Untagged on VLAN 10 | Untagged on VLAN 20 | Forward[a][b] |
| 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 | Forward[a] |
| Tagged on VLAN X | Tagged on VLAN Y | Drop (traffic from both VLANs) |
[a] Forwarding state applies if the link has not been blocked by RPVST+ as a redundant link. [b] If both sides (ports) of the link are untagged to different VLANs, but the VLAN on the switch on one end of the link is not RPVST+-enabled, untagged RPVST+ frames received on that switch port (where RPVST+ is disabled) would be forwarded to any other ports belonging to the inbound VLAN. | ||