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Ingress Rule:
Each packet received by a VLAN-aware bridge will be classified to a VLAN. The classification rule
is described as follows.
1. If the VID of the packet is null VID (VID=0)or this packet is an untagged packet:
a. If there are still some other ways(e.g. protocol, MAC address, application, IP-subnet, etc.) to
classify the incoming packets beside port-based classification in implement and these
approaches can offer non-zero VID, then, use the value of VID offered by other classifications
for VLAN’s classification.
b. If there is only port-based classification in implement or other classification approaches cannot
offer non-zero VID for the incoming packets, then assign the PVID to the incoming packets as
VID for the classification of the VLAN group.
2. If the VID is not a null VID (VID
≠
0), then use the value to classify the VLAN group.
Egress Rule:
An egress list is used to make the tagging and forwarding decision on an outgoing port. It specifies
the VLANs whose packets can be transmitted out and specifies if the packet should be tagged or not. It
can be configured for port’s VLAN membership, and tagged or untagged for a transmitted packet. When a
packet is transmitted out, the VLAN bridge checks the port’s egress list. If the VLAN of the packet is on
the egress list of the port on which the packet transmits out, the packet will be transmitted with the priority
accordingly. If enabled, an egress port will transmit out a tagged packet if the port is connected to a
802.1Q-compliant device. If an egress port is connected to a non-802.1Q device or an end station, VLAN
bridge must transmit out an untagged packet, i.e. the tag has been stripped off in an egress port. Egress
rule can be set by per port.
Independent VLAN Learning (IVL):
It specifies the mode how to learn MAC address. For a specified VLAN, it will use an independent
filtering database (FID) to learn or look up the membership information of the VLAN and decide where to
go.
Shared VLAN Learning (SVL):
It specifies the mode how to learn MAC address. In this mode, some VLAN or all VLANs use the
same filtering database storing the membership information of the VLAN to learn or look up the
membership information of the VLAN. In the 16-Port GbE Web Smart Switch, you can choose a VID for
sharing filtering database in Shared VID field if you wish to use the existing filtering database. For a
specified VLAN, when a MAC address is learned by a switch, VLAN will use this formation to make a
forwarding decision.
Filtering Database:
Referred to as FID. It can provide the information where the packet will be sent to. Filtering
databases will supply the outgoing port according to the request from forwarding process with VID and
DA. When a packet is received, if it has a non-zero VID, then FID will offer the associated outgoing ports
information to the packet.
In SVL, VLANs use the same Filtering Database. In IVL, VLANs use different FIDs. Any VID can
be assigned to the same FID by administrator.
How does a Tagged VLAN work?
If the ingress filtering is enabled and a packet is received, VLAN bridge will first check if the VID of
the packet is present.
1). If the packet has a non-zero VID, VLAN bridge will apply this VID as the VLAN
ID of the packet in the network.
2). For a packet with null tag or no VLAN tag, if VLAN bridge provides rules to
decide its VID, then apply this VID to the packet.
If VLAN bridge does not support any rule for VID, then apply the PVID of the port to the packet
which came from that port. VLAN bridge checks to see if the ingress port and the received packet are on
the same VLAN. If not, drops it. If yes, forwards it to the associated ports. Meanwhile, this VLAN must be
applied to the egress port, or the packet will be dropped.
