Antaira Technologies
– Enterprise Managed Media Converter
FCN-3112 Series User Manual V1.0
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6. Appendix A
A Virtual Local Area Network (VLAN) is a network topology configured according to a logical scheme
rather than the physical layout. VLAN can be used to combine any collections of LAN segments into a
group that appears as a single LAN. VLAN also logically segments the network into different
broadcast domains. All broadcast, multicast, and unknown packets entering the converter on a
particular VLAN will only be forwarded to the stations or ports that are members of that VLAN.
VLAN can enhance performance by conserving bandwidth and improve security by limiting traffic to
specific domains. A VLAN is a collection of end nodes grouped by logics instead of physical locations.
End nodes that frequently communicate with each other are assigned to the same VLAN, no matter
where they are physically located on the network. Another benefit of VLAN is that you can change the
network topology without physically moving stations or changing cable connections. Stations can be
‘moved’ to another VLAN and thus communicate with its members and share its resources, simply by
changing the port VLAN settings from one VLAN to another. This allows VLAN to accommodate
network moves, changes and additions with the greatest flexibility.
802.1Q VLAN Concept
Port-based VLAN is simple to implement and use, but it cannot be deployed across a network
containing several switches. The 802.1Q protocol was developed in order to provide the solution. By
tagging VLAN membership information to Ethernet frames, the IEEE 802.1Q can help network
administrators break large networks into smaller segments so that broadcast and multicast traffic will
not occupy too much available bandwidth as well as provide a higher-level security between
segments of internal networks.
Introduction to 802.1Q frame format:
Important VLAN Concepts for Configuration
There are two key concepts to understand.
1. The Default Port VLAN ID (
PVID
) specifies the VID that will be assigned to the untagged
traffic entering that port.
2. The VLAN ID (
VID
) specifies the set of VLANs that a given port is allowed to receive and
send.
Both variables can be assigned to a port, but there are significant differences between them.
Administrators can only assign one PVID to each port (since the 802.1Q protocol assigns any single
packet to just one VLAN). The PVID defines the default VLAN ID tag that will be added to un-tagged
