User`s guide

Signamax 065-7931 16-Port 10/100/1000BaseT/TX WebSmart Switch

How does a Tagged VLAN work?

If ingress filtering is enabled and when a packet is received, the VLAN bridge

will first check if the VID of the packet is presented.

1). If the packet has a non-zero VID, the VLAN bridge will apply this VID as the

VLAN ID of the packet in the network.

2). For a packet with a null tag or no VLAN tag, if the VLAN bridge provides rules to

decide its VID, then it will apply this VID to the packet.

If the VLAN bridge does not support any rule for VID, then apply the PVID of

the port to the packet which came from that port. The VLAN bridge checks to see if

the ingress port and the received packet are on the same VLAN. If not, it drops the

packet. If yes, it forwards the packet 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, the VLAN bridge will only check the MAC

address table to see if the destination VLAN exists. If the VLAN does not exist, it

then drops the packet, and if both the DA and VLAN do not exist, forwards the

packet. If it just knows VLAN existed, then it 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 used:

Name VID Port Members

Marketing 2 1,2,3,4,5

Service 3 6,7,20,21,22

Sales 4 8,9,10,11,12,13,14,15,16

Administration 1 17,18,19,23,24

Table 3-6

Next, the administrator assigns IP address to each VLAN. Usually, we use

10.x.x.x as internal IP block. Because there are total four VLANs in the network, we

must assign 4 IP blocks to each of them.

Name VID Network Address

Marketing 2 10.1.2.0/24

Service 3 10.1.3.0/24

Sales 4 10.1.4.0/24

Administration 1 10.1.1.0/24

Table 3-7

Here we apply the subnet mask 255.255.255, and each VLAN is then

capable of supporting 254 nodes.