Specifications

DGS-3212SR Stackable Gigabit Layer 2 Switch
Ingress Filtering
A port on a Switch where packets are flowing into the Switch and VLAN decisions must be made is referred to as an
ingress port. If ingress filtering is enabled for a port, the Switch will examine the VLAN information in the packet header
(if present) and decide whether or not to forward the packet.
If the packet is tagged with VLAN information, the ingress port will first determine if the ingress port itself is a member of
the tagged VLAN. If it is not, the packet will be dropped. If the ingress port is a member of the 802.1Q VLAN, the Switch
then determines if the destination port is a member of the 802.1Q VLAN. If it is not, the packet is dropped. If the
destination port is a member of the 802.1Q VLAN, the packet is forwarded and the destination port transmits it to its
attached network segment.
If the packet is not tagged with VLAN information, the ingress port will tag the packet with its own PVID as a VID (if the
port is a tagging port). The Switch then determines if the destination port is a member of the same VLAN (has the same
VID) as the ingress port. If it does not, the packet is dropped. If it has the same VID, the packet is forwarded and the
destination port transmits it on its attached network segment.
This process is referred to as ingress filtering and is used to conserve bandwidth within the Switch by dropping packets
that are not on the same VLAN as the ingress port at the point of reception. This eliminates the subsequent processing of
packets that will just be dropped by the destination port.
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