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DGS-3312SR
Инструкция по эксплуатации Страница: 101

D-Link DGS-3312SR [101/290] Ingress filtering

DGS-3312SR Stackable Gigabit Layer 3 Switch

Tag-aware

the VID o

Switches must keep a table to relate PVIDs within the Switch to VIDs on the network. The Switch will compare

f a packet to be transmitted to the VID of the port that is to transmit the packet. If the two VIDs are different, the

A Switch port can have only one PVID, but can have as many VIDs as the Switch has memory in its VLAN table to store

Because some devices on a network may be tag-unaware, a decision must be made at each port on a tag-aware device

Ports with tagging enabled will put the VID number, priority and other VLAN information into the header of all packets

that flow into and out of it. If a packet has previously been agged, the port will not alter the packet, thus keeping the

VLAN information i liant devices on the

network to make packet

evice to a non-compliant network device.

a member of the 802.1Q VLAN. If it is not, the packet is dropped. If the

he 802.1Q VLAN, the packet is forwarded and the destination port transmits it to its

f 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

dest n t.

This oce d to conserve bandwidth within the Switch by dropping packets

that are no point of reception. This eliminates the subsequent processing of

pack th

Switch will drop the packet. Because of the existence of the PVID for untagged packets and the VID for tagged packets,

tag-aware and tag-unaware network devices can coexist on the same network.

them.

before packets are transmitted – should the packet to be transmitted have a tag or not? If the transmitting port is connected

to a tag-unaware device, the packet should be untagged. If the transmitting port is connected to a tag-aware device, the

packet should be tagged.

Tagging and Untagging

Every port on an 802.1Q compliant Switch can be configured as tagging or untagging.

ntact. The VLAN information in the tag can then be used by other 802.1Q comp

forwarding decisions.

Ports with untagging enabled will strip the 802.1Q tag from all packets that flow into and out of those ports. If the packet

doesn’t have an 802.1Q VLAN tag, the port will not alter the packet. Thus, all packets received by and forwarded by an

untagging port will have no 802.1Q VLAN information. (Remember that the PVID is only used internally within the

Switch). Untagging is used to send packets from an 802.1Q-compliant network d

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

destination port is a member of t

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 i

inatio port transmits it on its attached network segmen

pr ss is referred to as ingress filtering and is use

t on the same VLAN as the ingress port at the

ets at will just be dropped by the destination port.

D-Link DGS-3312SR [101/290] Ingress filtering

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