Routing Models: Port-Based And Vlan-Based - 3Com corebuilder 3500 Implementation Manual

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HAPTER NTERNET
Routing Models:
Port-based and
VLAN-based
P (IP)
ROTOCOL
There are two basic routing models for implementing how a bridge and a
router interact within the same 3Com switch. They are:
Port-based routing (routing versus bridging) — The system first
tries to route packets that belong to recognized protocols, and all
other packets are bridged.
VLAN-based routing (routing over bridging) — The system first
tries to determine if the frame will be switched or routed. The system
does this by examining the destination MAC address:
If the destination MAC address is not an internal MAC address,
then the frame must be switched and is forwarded according to
the IEEE 802.1D protocol.
If the destination MAC address is an internal MAC address, the
frame is further examined to determine if the frame is a routed
frame (Layer 3) or a request to the switch itself (Layer 2).
This model allows the system to give the frame first to Layer 2 to be
bridged by the VLAN, and then given to the router only if the frame
cannot be bridged. This scheme gives you the flexibility to define
router interfaces on top of several bridge ports.
Your system, as a Layer 3 routing device, has the ability to implement
either type of routing scheme, "routing over bridging" and "routing
versus bridging." Each kind of routing scheme requires its own interface
type:
Routing over Bridging requires a VLAN-based IP Interface —
A VLAN-based interface requires you to first configure a VLAN and
then create a router interface over that VLAN.
Routing versus Bridging requires a Port-based IP Interface —
A port-based interface requires you to configure a router interface on
top of a single physical port.