D-Link DES-3326SRM Product Manual - Page 145

Port VLAN ID, Port VLAN ID PVID to forward packets.

Page 145 highlights

D-Link DES-3326S Layer 3 Switch The EtherType and VLAN ID are inserted after the MAC source address, but before the original EtherType/Length or Logical Link Control. Because the packet is now a bit longer than it was originally, the Cyclic Redundancy Check (CRC) must be recalculated. Port VLAN ID Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted from one 802.1Q compliant network device to another with the VLAN information intact. This allows 802.1Q VLANs to span network devices (and indeed, the entire network - if all network devices are 802.1Q compliant). Unfortunately, not all network devices are 802.1Q compliant. These devices are referred to as tag-unaware. 802.1Q devices are referred to as tag-aware. Prior to the adoption 802.1Q VLANs, port-based and MAC-based VLANs were in common use. These VLANs relied upon a Port VLAN ID (PVID) to forward packets. A packet received on a given port would be assigned that port's PVID and then be forwarded to the port that corresponded to the packet's destination address (found in the Switch's forwarding table). If the PVID of the port that received the packet is different from the PVID of the port that is to transmit the packet, the Switch will drop the packet. Within the Switch, different PVIDs mean different VLANs. (remember that two VLANs cannot communicate without an external router). So, VLAN identification based upon the PVIDs cannot create VLANs that extend outside a given Switch (or Switch stack). Every physical port on a Switch has a PVID. 802.1Q ports are also assigned a PVID, for use within the Switch. If no VLANs are defined on the Switch, all ports are then assigned to a default VLAN with a PVID equal to 1. Untagged packets are assigned the PVID of the port on which they were received. Forwarding decisions are based upon this PVID, in so far as VLANs are concerned. Tagged packets are forwarded according to the VID contained within the tag. Tagged packets are also assigned a PVID, but the PVID is not used to make packet forwarding decisions, the VID is. Tag-aware Switches must keep a table to relate PVIDs within the Switch to VIDs on the network. The Switch will compare the VID of a packet to be transmitted to the VID of the port that is to transmit the packet. If the two VIDs are different, the 135

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D-Link DES-3326S Layer 3 Switch
The EtherType and VLAN ID are inserted after the MAC source address, but before the original EtherType/Length or Logical
Link Control.
Because the packet is now a bit longer than it was originally, the Cyclic Redundancy Check (CRC) must be
recalculated.
Port VLAN ID
Packets that are tagged (are carrying the 802.1Q VID information) can be transmitted from one 802.1Q compliant network
device to another with the VLAN information intact. This allows 802.1Q VLANs to span network devices (and indeed, the
entire network – if all network devices are 802.1Q compliant).
Unfortunately, not all network devices are 802.1Q compliant.
These devices are referred to as
tag-unaware.
802.1Q devices
are referred to as
tag-aware.
Prior to the adoption 802.1Q VLANs, port-based and MAC-based VLANs were in common use.
These VLANs relied upon a
Port VLAN ID (PVID) to forward packets.
A packet received on a given port would be assigned that port’s PVID and then be
forwarded to the port that corresponded to the packet’s destination address (found in the Switch’s forwarding table).
If the
PVID of the port that received the packet is different from the PVID of the port that is to transmit the packet, the Switch will
drop the packet.
Within the Switch, different PVIDs mean different VLANs.
(remember that two VLANs cannot communicate without an
external router). So, VLAN identification based upon the PVIDs cannot create VLANs that extend outside a given Switch (or
Switch stack).
Every physical port on a Switch has a PVID. 802.1Q ports are also assigned a PVID, for use within the Switch.
If no VLANs
are defined on the Switch, all ports are then assigned to a default
VLAN with a PVID equal to 1. Untagged packets are
assigned the PVID of the port on which they were received.
Forwarding decisions are based upon this PVID, in so far as
VLANs are concerned.
Tagged packets are forwarded according to the VID contained within the tag.
Tagged packets are also
assigned a PVID, but the PVID is not used to make packet forwarding decisions, the VID is.
Tag-aware Switches must keep a table to relate PVIDs within the Switch to VIDs on the network.
The Switch will compare
the VID of a packet to be transmitted to the VID of the port that is to transmit the packet.
If the two VIDs are different, the
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