3Com 4007, Implementation Manual, Page: 256 / 684

256 C
HAPTER
14: V
IRTUAL
LAN
S
(VLAN
S
)
Number of VLANs You must evaluate the number of VLANs on a per-module basis. The
module type determines the number of VLANs that can be supported:
■
Each Layer 2 switching module supports a maximum of 127
port-based VLANs.
■
Each Multilayer switching module use the following equation to
determine the number of VLANs that are supported.
Equation for VLANs on Multilayer Switching Modules
To determine the number of VLANs of any type that you can have on a
Multilayer Switching Module, use the following equation:
No._of_VLANs_supported = (125 / No._of_Protocol_Suites) minus 3
When you use the VLAN equation to calculate the number of VLANs that
you may have on your Multilayer Switching Module, keep in mind that
the formula provides only an estimate. You may see more or fewer
VLANs, depending on your configuration, use of protocol suites, and
chosen tag style. If, for example, you are using the Release 3.0 VLAN tag
style of all ports, this formula generally yields a maximum; if you change
to use the Release 1.2 tag style of taggedVlanPorts, then this formula
generally yields a minimum number of VLANs.
A result of up to 64 is valid. If your result is greater than 64, you must
observe 64 as the limit for the number of VLANs supported.
The number of allowable VLANs includes the default VLAN, and the
number of protocol suites always includes the
unspecified protocol type.
To perform the calculation, determine the total number of protocol suites
used on your system. Remember to include the
unspecified type for the
default VLAN, even if you have removed the default VLAN and do not
have other VLAN defined with the unspecified protocol type.
Use the following guidelines to count the protocol suites that are used on
the Multilayer Switching Module:
■
IP counts as one protocol suite for IP VLANs.
■
AppleTalk counts as one protocol suite for AppleTalk VLANs.
■
Generic IPX, which uses all four IPX types, counts as four protocol
suites. (Each IPX type alone counts as one.) To conserve VLAN
resources, it is better to specify a specific IPX frame type than to use
generic IPX.