I have been trying to understand ingress behaviour on untagged port, specially w.r.t tagged frames. On going through ieee 802.1q doc, i found this (8.6.2) : "Each Port may support an Enable Ingress Filtering parameter. A frame received on a Port that is not in the member set (8.8.9) associated with the VID shall be discarded if this parameter is set. The default value for this parameter is reset, i.e., Disable Ingress Filtering, for all Ports. Any Port that supports setting this parameter shall also support resetting it. The parameter may be configured by the management operations defined in Clause 12." It only speaks about VID of incoming frame . From that, My understanding is, incoming frame (whether it is tagged or untagged / irrespective of port type ) must be looked upon VLAN database and forwarded /discarded accordingly. Furthermore, the doc mainly defines functionality of a port in terms of a Bridge, and only classifies them as VLAN aware and unaware types (Here again , i assume, trunk and access type respectively). It also specfies that an untagged traffic is associated(assume tagged) with PVID of that particular port. It doesn't effectively specify the scenario of tagged traffic on to the untagged port. However, most of online forums say that a untagged port should discard tagged frames, (some say with exception of native vlan). !! I am confused a bit, since the standard doesn't specify this kind of behaviour. So can anyone clear up some air on this!!?.
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