User guide

IP Forwarding Configuring IP
page 13-6 OmniSwitch 6600 Family Network Configuration Guide April 2005
IP Forwarding
Network device traffic is bridged (switched) at the Layer 2 level between ports that are assigned to the
same VLAN. However, if a device needs to communicate with another device that belongs to a different
VLAN, then Layer 3 routing is necessary to transmit traffic between the VLANs. Bridging makes the deci-
sion on where to forward packets based on the packet’s destination MAC address; routing makes the deci-
sion on where to forward packets based on the packet’s IP network address (e.g., IP - 21.0.0.10).
Alcatel switches support routing of IP traffic. A VLAN is available for routing when at least one router
interface is defined for that VLAN and at least one active port is associated with the VLAN. Each VLAN
supports one IP router interface and a maximum of 4094 IP router VLANs are allowed per switch.. If a
VLAN does not have a router interface, the ports associated with that VLAN are in essence firewalled
from other VLANs.
In the illustration below, an IP router interface has been configured on each VLAN. Therefore, worksta-
tions connected to ports on VLAN 1 on Switch 1 can communicate with VLAN 2; and workstations
connected to ports on VLAN 3 on Switch 2 can communicate with VLAN 2. Also, ports from both
switches have been assigned to VLAN 2, and a physical connection has been made between the switches.
Therefore, workstations connected to VLAN 1 on Switch 1 can communicate with workstations connected
to VLAN 3 on Switch 2.
IP Forwarding
OmniSwitch 6648OmniSwitch 6648
Switch 2
130.0.0.1 130.0.0.2
VLAN 3
130.0.0.0
Switch 1
VLAN 1
110.0.0.0
110.0.0.1 110.0.0.2
Physical
Connection
IP Router Interface
=
VLAN 2
120.0.0.0
VLAN 2
120.0.0.0