Role Of Vlans In Ip Routing - 3Com corebuilder 3500 Implementation Manual

Role of VLANs in
IP Routing
It is important to keep in mind that, except for the out-of-band
management port, there is a VLAN index associated with every IP
interface, whether the interface is port-based or VLAN-based:
Port-based router interface — The system creates a VLAN index
and associates it with the interface as you define the router interface.
The hardware requires that every packet be associated with a VLAN
ID. Even though port-based packets do not use VLAN software, the
hardware must recognize the packets as VLAN entities. Therefore, the
system configures every router port interface as a single port,
nontagged, protocol-based VLAN.
VLAN-based router interface — You explicitly create a VLAN index,
then define the IP interface and associate the interface with the index.
In addition, port-based routing requires the VLANs on a system to be in
AllClosed mode. This potentially has major effects on your network
configuration. For more information about allClosed and allOpen mode
with regard to IP routing, see "Important Considerations" later in this
chapter.
Routing Models: Port-based and VLAN-based 275