Understanding Bridge Behavior: Why PVID Matters

When configuring a bridge in Mikrotik, understanding how it handles packets is crucial to ensure proper network operation. One aspect that can be puzzling is the behavior of seemingly untagged packets on the bridge interface. However, this behavior can be simplified by setting the pvid parameter correctly.

In previous versions of Mikrotik's router operating system, bridges were essentially dumb switches, which would happily utilize packets belonging to VLAN ID 1 (untagged) just like explicitly untagged packets. This led some users to assume that VLAN ID 1 was always treated as untagged by the bridge interface. However, this assumption is not entirely accurate.

The key to understanding bridge behavior lies in setting the pvid parameter correctly. By default, the pvid value is set to 1, which may seem unusual at first. However, this setting is actually a result of how bridges handled packets in previous versions. If you change the bridge's own pvid to something other than 1, VLAN ID 1 will behave normally.

It's essential to note that it's not VLAN ID 1 that is always treated as untagged by the bridge interface; rather, it's the VLAN ID configured as the bridge's own pvid parameter that is treated as untagged. This may seem counterintuitive, but it's a design choice made by Mikrotik.

In conclusion, understanding how bridges handle packets requires attention to detail when configuring the pvid parameter. By setting this value correctly, you can ensure proper network operation and avoid potential issues related to seemingly untagged packets on your bridge interface.

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