Specifications

Engineering Guidelines
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packets with that VLAN setting.
- The phone will obtain the necessary VLAN configuration in a number of ways,
highlighted later, but essentially through one of the following: Static programming,
DHCP, LLDP-MED, or CDP broadcasts.
- While the IEEE specification allows for VLANs from 0 to 4095, not all vendors support
this range. As a general rule, VLAN 0 is treated in different ways by different vendors.
The recommendation is not to use VLAN 0. Cisco also reserves VLAN 1000 and
upward for Cisco purposes, so ensure there is not a conflict when using these higher
VLAN numbers.
• Multi-VLAN port
- Cisco devices provide this as another port configuration. However, on some of the
access switches it is not possible to use multi-VLAN ports and trunk ports on the same
unit. Unfortunately, the multi-VLAN port type is needed in order to work with other
vendor products. A trunk port can be used, but it also removes tagging from the
configured native VLAN, which may not be what is required. An example is a port
configured with the native_VLAN to 1. On ingress, tagging is added, but on egress it
is removed. Tagging information should be maintained through the network, only
being modified at the access points. Removing tagging between switches is not
desirable. There are two possible ways out of this situation:
a. Run Cisco ISL between the two units (but then they both need to be Cisco).
or
b. Create a dummy native_VLAN (tag native_VLAN) that is not used anywhere else
in the network to ensure compatibility with other vendor units and allow products
to be mixed. The dummy VLAN does not carry data since there are no end devices
configured with this VLAN. This effectively turns the trunk port into a multi-VLAN
port for the desired VLAN connections.
HP port examples
The HP switch uses a similar RS232 connection, but the user interface is more menu-driven
making the configuration more intuitive. The following figure shows a typical screen display.
Figure 31: HP Screen Display Example