Ingress Filtering; Default Vlans; Port-Based Vlans - D-Link DGS-3324SR User Manual

D-Link DGS-3324SR Layer 3 Stackable Gigabit Ethernet 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.

Default VLANs

The Switch initially configures one VLAN, VID = 1, called "default." The factory default setting assigns all
ports on the Switch to the "default." As new VLANs are configured in Port-based mode, their respective member
ports are removed from the "default."
Packets cannot cross VLANs. If a member of one VLAN wants to connect to another VLAN, the link must be
through an external router.
Note: If no VLANs are configured on the Switch, then all packets will be
forwarded to any destination port. Packets with unknown source
addresses will be flooded to all ports. Broadcast and multicast packets will
also be flooded to all ports.
An example is presented below:
VLAN Name
System (default)
Engineering
Marketing
Finance
Sales

Port-based VLANs

Port-based VLANs limit traffic that flows into and out of switch ports. Thus, all devices connected to a port are
members of the VLAN(s) the port belongs to, whether there is a single computer directly connected to a switch,
or an entire department.
VID Switch Ports
1 5, 6, 7, 8, 21, 22, 23, 24
2 9, 10, 11, 12
3 13, 14, 15, 16
4 17, 18, 19, 20
5 1, 2, 3, 4
Table 4- 2. VLAN Example – Assigned Ports
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