D-Link DES-3624 - Switch - Stackable User manual - page 68
Stackable NWay Ethernet Switch User’s Guide
compliant and whether VLAN packets should be tagged or
untagged.
Definitions of relevant terms are as follows:
♦ Tagging The act of putting 802.1Q VLAN information into
the header of a packet. Ports with tagging enabled will put
the VID number, priority, and other VLAN information into
all packets that flow into and out it. If a packet has
previously been tagged, the port will not alter the packet,
thus keeping the VLAN information intact. Tagging is used
to send packets from one 802.1Q-compliant device to
another.
♦ Untagging The act of stripping 802.1Q VLAN information
out of the packet header. Ports with untagging enabled will
take all VLAN information out of all packets that flow into
and out of a port. If the packet doesn’t have a VLAN tag, the
port will not alter the packet, thus keeping the packet free of
VLAN information. Untagging is used to send packets from
an 802.1Q-compliant switch to a non-compliant device.
♦ Ingress port A port on a switch where packets are flowing
into the switch and VLAN decisions must be made.
Basically, the switch examines VLAN information in the
packet header (if present) and decides whether 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 and can thus receive the
packet (if the Ingress Filter is enabled), and then it decides if
the destination port is a member of the VLAN. Assuming
both ports are members of the tagged VLAN, the packet will
be forwarded. If the packet doesn’t have VLAN information
in its header (is untagged), the ingress port first determines
if the ingress port itself can receive the packet (if the Ingress
Filter is enabled), will tag it with its own PVID (if it defined
as a tagging port), and check to see if the destination port is
on the same VLAN as its own PVID and can thus receive the
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Switch Management Concepts