Vlan; Automatic Vlan Discovery (Dhcp) - Siemens HiPath 2000 Administration Manual

3.2.2

VLAN

VLAN (Virtual Local Area Network) is a technology that allows network administrators to parti-
tion one physical network into a set of virtual networks (or broadcast domains).
Physically partitioning the LAN into separate VLANs allows a network administrator to build a
more robust network infrastructure. A good example is a separation of the data and voice net-
works into data and voice VLANs. This isolates the two networks and helps shield the end-
points within the voice network from disturbances in the data network and vice versa.
The implementation of a voice network based on VLANs requires the network infra-
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structure (the switch fabric) to support VLANs.
In a layer 1 VLAN, the ports of VLAN-aware switch are assigned to a VLAN statically. The
switch only forwards traffic to a particular port if that port is a member of the VLAN that the traffic
is allocated to. Any device connected to a VLAN-assigned port is automatically a member of
this VLAN, without being a VLAN aware device itself. If two or more network clients are con-
nected to one port, they cannot be assigned to different VLANs. When a network client is mov-
ing from one switch to another, the switches' ports have to be updated accordingly by hand.
With a layer 2 VLAN, the assignment of VLANs to network clients is realized by the MAC ad-
dresses of the network devices. In some environments, the mapping of VLANs and MAC ad-
dresses can be stored and managed by a central database. Alternatively, the VLAN ID, which
defines the VLAN whereof the device is a member, can be assigned directly to the device, e. g.
by DHCP. The task of determining the VLAN an Ethernet packet is belonging to is carried out
by VLAN tags within each Ethernet frame. As the MAC addresses are (more or less) wired to
the devices, mobility does not require any administrator action, as opposed to layer 1 VLAN. It
is possible to assign one device, i.e. one MAC address, to different VLANs.
It is important that every switch connected to a PC is VLAN-capable. This is also true for the
integrated switch of the OpenStage phone. The phone must be configured as a VLAN aware
endpoint if the phone itself is a member of the voice VLAN, and the PC connected to the
phone's PC port is a member of the data VLAN.
3.2.2.1

Automatic VLAN discovery (DHCP)

To automatically discover a VLAN ID using DHCP, the phone must be configured as DHCP en-
abled, and VLAN discovery mode must be set to "DHCP". This is the default configuration.
The DHCP server must be configured to supply the Vendor Unique Option in the correct Sie-
mens VLAN over DHCP format. If a phone configured for VLAN discovery by DHCP fails to dis-
cover its VLAN, it will proceed to configure itself from the DHCP within the non-tagged LAN. In
these circumstances network routing will probably not be correct.
A31003-S2010-M100-10-7619, 27/08/2008
HiPath 2000/3000/5000 - OpenStage Family, Administration Manual
administration.fm
Administration
LAN Settings
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