D-Link DES-6300 User Manual page 32

Modular L3 Ethernet Switch User's Guide
Port PVID
Port 1 1
Port 4 1
Port 13 2
Port 16 2
Port 9 3
Ports VID
1,4,9 1
9,13,16 2
1,4,9,13, 3
16
Table 5-2. VLAN assignments for Figure 5-4
The server attached to Port 9 is shared by VLAN 1 and VLAN 2 because Port 9 is a member of both
VLANs (it is listed as a member of VID 1 and 2). Since it can receive packets from both VLANs, all ports
can successfully send packets to it. Ports 1 and 4 send these packets on VLAN 1 (their PVID=1), and
Ports 13 and 16 send these packets on VLAN 2 (PVID=2). The third VLAN (PVID=3) is used by the server
to transmit files that had been requested on VLAN 1 or 2 back to the computers. All computers that use
the server will receive transmissions from it since they are all located on ports which are members of
VLAN 3 (VID=3).
802.1Q VLANs Spanning Multiple Switches
802.1Q VLANs can span multiple switches as well as your entire network. Two considerations to keep
in mind while building VLANs of this sort are whether the switches are IEEE 802.1Q-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. Tagging ports 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. Untagging ports
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. If an ingress port has
the Ingress Filter enabled, the switch will examine each packet to determine whether or not it is a
VLAN member and then take one of two actions: if the port is not a member of a VLAN, the packet
will be dropped; if the port is a member of a VLAN, then the packet will be forwarded. Otherwise, if
the Ingress Filter is disabled, then the switch will process any packet received at this port in its
normal fashion.
♦ 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 an
802.1Q-compliant device, tagging should be enabled so the other device can take VLAN data into
account when making forwarding decisions (this allows VLANs to span multiple switches). If an
egress connection is to a non-compliant switch or end-station, tags should be stripped so the (now
normal Ethernet) packet can be read by the receiving device.
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