Vlan Overview; Choosing Dhcp For Vlan - Nortel BCM50 Configuration Manual

Chapter 64

VLAN overview

A virtual LAN (VLAN) is a logical grouping of ports, controlled by a switch, and end-stations,
such as IP telephones, configured so that all ports and end-stations in the VLAN appear to be on
the same physical (or extended) LAN segment even though they may be geographically separated.
VLAN IDs are determined by how the VLAN switch is configured. If you are not the network
administrator, you must ask whoever manages the switch what the VLAN ID range is for your
system.
VLANs aim to offer the following benefits:
• VLANs are supported over all IEEE 802 LAN MAC protocols, and over shared media LANs
as well as point-to-point LANs.
• VLANs facilitate easy administration of logical groups of stations that can communicate as if
they were on the same LAN. They also facilitate easier administration of move, add, and
change in members of these groups.
• Traffic between VLANs is restricted. Bridges forward unicast, multicast, and broadcast traffic
only on LAN segments that serve the VLAN to which the traffic belongs.
• For IP telephony, VLANs provide a useful technique to separate and prioritize the telephony
traffic for L2 switches.
• VLAN also provides a shield from malicious traffic that may be targeted at the IP phone in
order to steal or disrupt service.
• Reuse IP addresses in different VLANs.
• As far as possible, VLANs maintain compatibility with existing bridges and end stations.
• If all bridge ports are configured to transmit and receive untagged frames, bridges will work in
plug-and-play ISO/IEC 15802-3 mode. End stations are able to communicate throughout the
Bridged LAN.

Choosing DHCP for VLAN

By using the BCM DHCP server, you can configure DHCP to auto-assign a VLAN ID to each IP
telephone that registers. With this configuration, you can also choose to manually enter VLAN
IDs, if you choose. The BCM DHCP server becomes the default VLAN that everyone can reach.
The server provides the network configuration information in the default VLAN, and it also
provides the VLAN information for the network.
Networking Configuration Guide
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