3Com corebuilder 3500 Implementation Manual page 168

168 C 9: V LAN
HAPTER IRTUAL S
To establish routing between static VLANs and configure a VLAN
interface to support one or more routing protocols, configure the
VLAN for the protocols before you configure a routing interface. For
protocols other than IP, the system does not define the routing
interface for a protocol if a VLAN for that protocol does not exist.
If you define an IP interface and specify vlan as the interface type, the
system does not define the IP routing interface unless you have an IP
VLAN configured. See the appropriate routing chapter for an overview
of your routing options and guidelines. See Chapter 11 for
information on defining either an IP router interface (for a static IP
VLAN) or a router port IP interface.
If you plan to use trunks, define the appropriate trunks before you
define your VLANs. (If you define a VLAN with certain ports and
subsequently configure some of those ports to be part of a trunk, the
system removes those ports from the VLAN and places them in the
default VLAN.) See "Trunking and the Default VLAN" for more
information. When you define a VLAN that includes trunk ports, you
must specify the trunk's anchor port (lowest-numbered port). For
trunking information, see Chapter 8.
When the system receives a frame, the frame is assigned to a VLAN
using the ingress rules. See "Ingress Rules" later in this chapter. When
the system transmits the frame, it determines the tag status (none or
IEEE 802.1Q tagging) by referring to the tag status of the transmit
port in the frame's assigned VLAN. In allOpen mode, if a frame is
transmitted on a port that does not belong to the assigned VLAN, the
frame is transmitted untagged.