3Com CoreBuilder 3500, Implementation Manual, Page: 176 / 592

176 C
HAPTER
9: V
IRTUAL
LAN
S
The default VLAN is the flood domain in either of these cases:
■
The system receives data for a protocol that is not supported by any
VLAN in the system.
■
The system receives data for a protocol that is supported by defined
VLANs, but these VLANs do not contain the port receiving the data.
See “Rules of VLAN Operation” later in this chapter.
Modifying the Default VLAN
The default VLAN is always associated with the VID of 1, the unspecified
protocol type, and the name
Default
. Initially, the default VLAN is also
associated with all ports and no tagging. Keeping the default VLAN intact
ensures that the system accommodates the addition of a module by
automatically adding the new module’s bridge ports to the default VLAN.
If necessary, the system also renumbers its ports when you add the
module.
If necessary, you can modify (or remove) the default VLAN on the system.
For example, you may want to modify the default VLAN to remove certain
ports. Such a change does not prevent the system from adding a new
module’s bridge ports to the default VLAN.
However, the following changes do prevent the system from adding a
new module’s bridge ports to the default VLAN:
■
If you modify the default VLAN to remove all ports
■
If you remove the default VLAN completely. Even if you subsequently
redefine the default VLAN, the system will not add bridge ports to the
newly defined default VLAN.
■
If you modify the default VLAN to tag a port
To ensure that data can be forwarded, associate a bridge port with a
VLAN. This association is mandatory in allClosed mode. If you remove the
default VLAN (and you do not have other VLANs defined for the system),
your ports may not forward data until you create a VLAN for them.