
Stackable NWay Ethernet Switch User’s Guide
46
Switch Management Concepts
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.
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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.
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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
packet. If Ingress filtering is disabled and the destination port is a
member of the VLAN used by the ingress port, the packet will be
forwarded. If the ingress port is an untagging port, it will only
check the filter condition--if the filter condition is enabled-- before
forwarding the packet.
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Egress port
A port on a switch where packets are flowing out of
the switch, either to another switch or to an end station, and
tagging decisions must be made. If an egress port is connected to
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