Publication date: Mar. 2016
33600 Rev B
38
Independent VLAN Learning (IVL):
It specifies the mode how to learn MAC address. For a specified VLAN, it will
use an independent filtering database (FID) to learn or look up the membership
information of the VLAN and decide where to go.
Shared VLAN Learning (SVL):
It specifies the mode how to learn MAC address. In this mode, some VLAN
or all VLANs use the same filtering database storing the membership information of
the VLAN to learn or look up the membership information of the VLAN. In
SM24TAT4GPA, you can choose a VID for sharing filtering database in Shared VID
field if you wish to use the existed filtering database. For a specified VLAN, when a
MAC address is learned by a switch, VLAN will use this formation to make
forwarding decision.
Filtering Database:
Referred to as FID. It can provide the information where the packet will be
sent to. Filtering database will supply the outgoing port according to the request
from forwarding process with VID and DA
.
When a packet is received, if it has a
non-zero VID, then FID will offer the associated outgoing ports information to the
packet.
In SVL, VLANs use the same Filtering Database. In IVL, VLANs use different
FIDs. Any VID can be assigned to the same FID by administrator.
How does a Tagged VLAN work?
If the ingress filtering is enabled and when a packet is received, VLAN bridge
will first check if the VID of the packet presents.
1). If the packet has a non-zero VID, VLAN bridge will apply this VID as the VLAN
ID of the packet in the network.
2). For a packet with null tag or no VLAN tag, if VLAN bridge provides rules to
decide its VID, then apply this VID to the packet.
If VLAN bridge does not support any rule for VID, then apply the PVID of the
port to the packet which came from that port. VLAN bridge checks to see if the
ingress port and the received packet are on the same VLAN. If not, drops it. If yes,
forwards it to the associated ports. Meanwhile, this VLAN must be applied to the
egress port, or the packet will be dropped.
If ingress filtering is disabled, VLAN bridge will only check the MAC address
table to see if the destination VLAN exists. If VLAN does not exist, then drop the
packet, and if both DA and VLAN do not exist, forwards the packet. If just knows
VLAN existed, then floods the packet to all the ports the VLAN covers.
If we plan to deploy four VLANs in an office and use a switch to partition
them, we should check which ports belong to which VLAN first. Assuming a 24-port
switch is applied.
