Alcatel-Lucent OmniSwitch 6800 Series - IP Forwarding

Configuring IP IP Forwarding
OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008 page 18-7
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
decision on where to forward packets based on the packet’s destination MAC address; routing makes the
decision on where to forward packets based on the packet’s IP network address (e.g., IP - 21.0.0.10).
Alcatel-Lucent 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. If a
VLAN does not have a router interface, the ports associated with that VLAN are in essence firewalled
from other VLANs.
IP multinetting is also supported. A network is said to be multinetted when multiple IP subnets are brought
together within a single broadcast domain. It is now possible to configure up to eight IP interfaces per
VLAN. Each interface is configured with a different subnet. As a result, traffic from each configured
subnet can coexist on the same VLAN.
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
If the switch is running in single MAC router mode, a maximum of 4094 VLANs can have IP interfaces
defined and a maximum of 64 VLANs can have IPX interfaces defined. In this mode, each router VLAN
is assigned the same MAC address, which is the base chassis MAC address for the switch.
See Chapter 4, “Configuring VLANs,” for more information about configuring the IPX router interfaces.
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