3Com 1100 - Manual (Page 168)

168 C HAPTER 6: V IRTUAL LAN S (VLAN S )
The system works as follows:
1 The configured 802.1Q endstation sends out a packet with a known
multicast address to the whole network — this packet declares that the
endstation is to receive traffic for specific VLANs.
2 When the packet arrives at a port on a Switch with 802.1Q learning
enabled, the Switch places the receiving port in the VLANs specified and
then forwards the packet to all other ports.
3 When the packet arrives at another Switch with 802.1Q learning
enabled, it also places the receiving port in the VLANs specified and
forwards the packet to all other ports. In this way the VLAN information is
propagated throughout the network, and the required VLAN traffic can
always reach the endstation from anywhere in the network.
For information about enabling 802.1Q learning for an individual port on
your Switch, see
“Configuring a Port” on page 59 . For information about
enabling 802.1Q learning for a whole Switch or stack, see “Configuring
the Advanced Stack Settings” on page 76 .
For information about configuring IEEE 802.1Q functionality on an
endstation, refer to the user documentation supplied with your
endstation or the endstation’s Network Interface Card (NIC).
Forwarding Traffic
Containing Unknown
802.1Q Tags
Your Switch supports up to 16 VLANs, however the IEEE 802.1Q standard
allows up to 4,094 VLANs to be defined on a network. If your network
contains endstations that support 802.1Q, the Switch may need to
forward traffic that uses unknown 802.1Q tags. This traffic is
automatically forwarded if your Switch has 802.1Q learning enabled, but
is not if 802.1Q learning is disabled.
To specify that a port can forward traffic containing unknown tags when
802.1Q learning is disabled, see
“Configuring a Port” on page 59 . We
recommend that you only forward unknown tags on ports connected to
switch units that support IEEE 802.1Q (as shown in
Figure 32 ).