Siemens HIPATH 8000 - Manual (Page 44)

Technical Overview
44
IP Network Configuration
Routing
The phone allows a default route to be configured to allow access to Serv-
ers on a different subnet to the one in which the phone resides. In addition
it is possible to configure 2 additional routes. Each route consists of a IP
address, gateway and mask.
Virtual LAN (VLAN)
VLAN or virtual LAN is a technology that allows network administrators to
partition one physical network into a set of virtual networks (or broadcast
domains).
Physically partitioning the LAN into separate VLANs allows a network ad-
ministrator to build a more robust network infrastructure. A good example
is of the data and voice networks being partitioned into data and voice
VLANs. This isolates the two networks and helps shield the endpoints
within the voice network from disturbances in the data network and vice
versa.
VLAN is a layer 2 (Physical Layer) protocol. In the case of Ethernet the
physical header is extended allowing endpoints to be not only be ad-
dressed via MAC address, but also VLAN ID Æ page 203. Ethernet VLANs
support the partitioning of a physical LAN into up to 4095 virtual LANs.
To implement a voice network based on VLANs requires the network infra-
structure (the switch fabric) to support VLANs at layer 2. Dependant on the
overall architecture it may or may not be necessary for the endpoint
(phone) to support layer 2 VLAN.
The ports of the network switches in the switch fabric can be logically
grouped as ports belonging to particular VLAN. The switch only forwards
traffic to a particular port if that port is a member of the VLAN that the traf-
fic is allocated to. In this way an endpoint connected to a particular port on
the switch is automatically a member of that VLAN without being a VLAN
aware device; the switch ensures the endpoint only receives traffic for that
VLAN and ensures traffic from the endpoint is only forwarded to ports that
are configured to be in the same VLAN. This is known as port based VLAN
in the switch world.
When multiple endpoints are connected to a single network switch port
and these endpoints belong to multiple VLANs then a different approach is
needed to implement a VLAN based topology. A typical example or this is
a phone with a PC connected behind the phone. The phone would be a
member of the Voice VLAN and the PC a member of the data VLAN. In
this case the Phone must be configured as a VLAN aware endpoint.