Vlan-Based Routing - 3Com corebuilder 3500 Implementation Manual

280 C 11: I
HAPTER NTERNET

VLAN-based Routing

P (IP)
ROTOCOL
You can only remove a VLAN associated with a router port interface
using
ip interface remove
bridge vlan remove
port VLAN from inadvertent deletion.
The ip interface summary must display the parameters of both
VLAN-based and port-based IP interfaces. For this reason, the field
labeled displays the VLAN interface index (if the interface type
ID
equals ) or displays the physical port number (if the interface type
VLAN
equals ).
Port
In VLAN-based routing, the destination MAC address determines whether
the system bridges or routes a packet. Before a host system sends a
packet to another host, the host system compares its own network
address to the network address of the other host as follows:
If network addresses are on the same subnet, the packet is bridged
directly to the destination address of the host.
If network addresses are on different subnets, the packet must be
routed from one to the other. In this case, the host sends an ARP
request for its gateway MAC address, then transmits the packet using
the MAC address of the gateway.
Figure 52 illustrates the process when the packet is routed:
1 The packet enters the system.
2 The bridging layer examines the destination MAC address of the packet.
The destination MAC address corresponds to the address of one of the
system ports that are configured for routing (as opposed to a learned end
station address).
3 The packet is passed to the router interface that is associated with the
port where the packet was received.
4 The routing layer:
a Selects a destination interface based on the destination network
address
b Determines the MAC address of the next hop (either the destination
host or another gateway)
c Passes the packet back to the bridging layer using the destination
MAC address of the next hop
. If you try to remove the VLAN using
, an error is returned. This protects the router