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Configuring Virtual LANs (VLANs)
December 2005
© Foundry Networks, Inc.
11 - 5
Integrated Switch Routing (ISR)
Foundry Networks’
Integrated Switch Routing (ISR)
feature enables VLANs configured on Layer 3 Switches to
route Layer 3 traffic from one protocol VLAN or IP sub-net, IPX network, or AppleTalk cable VLAN to another.
Normally, to route traffic from one IP sub-net, IPX network, or AppleTalk cable VLAN to another, you would need to
forward the traffic to an external router. The VLANs provide Layer 3 broadcast domains for these protocols but do
not in themselves provide routing services for these protocols. This is true even if the source and destination IP
sub-nets, IPX networks, or AppleTalk cable ranges are on the same device.
ISR eliminates the need for an external router by allowing you to route between VLANs using virtual routing
interfaces (ves). A
virtual routing interface
is a logical port on which you can configure Layer 3 routing
parameters. You configure a separate virtual routing interface on each VLAN that you want to be able to route
from or to. For example, if you configure two IP sub-net VLANs on a Layer 3 Switch, you can configure a virtual
routing interface on each VLAN, then configure IP routing parameters for the sub-nets. Thus, the Layer 3 Switch
forwards IP sub-net broadcasts within each VLAN at Layer 2 but routes Layer 3 traffic between the VLANs using
the virtual routing interfaces.
NOTE:
The Layer 3 Switch uses the lowest MAC address on the device (the MAC address of port 1 or 1/1) as the
MAC address for all ports within all virtual routing interfaces you configure on the device.
The routing parameters and the syntax for configuring them are the same as when you configure a physical
interface for routing. The logical interface allows the Layer 3 Switch to internally route traffic between the protocol-
based VLANs without using physical interfaces.
All the ports within a protocol-based VLAN must be in the same port-based VLAN. The protocol-based VLAN
cannot have ports in multiple port-based VLANs, unless the ports in the port-based VLAN to which you add the
protocol-based VLAN are 802.1Q tagged.
You can configure multiple protocol-based VLANs within the same port-based VLAN. In addition, a port within a
port-based VLAN can belong to multiple protocol-based VLANs of the same type or different types. For example,
if you have a port-based VLAN that contains ports 1 – 10, you can configure port 5 as a member of an AppleTalk
protocol VLAN, an IP protocol VLAN, and an IPX protocol VLAN, and so on.
IP Sub-Net, IPX Network, and AppleTalk Cable VLANs
The protocol-based VLANs described in the previous section provide separate protocol broadcast domains for
specific protocols. For IP, IPX, and AppleTalk, you can provide more granular broadcast control by instead
creating the following types of VLAN:
•
IP sub-net VLAN
– An IP sub-net broadcast domain for a specific IP sub-net.
•
IPX network VLAN
– An IPX network broadcast domain for a specific IPX network.
•
AppleTalk cable VLAN
– An AppleTalk broadcast domain for a specific cable range.
You can configure these types of VLANs on Layer 3 Switches only. The Layer 3 Switch sends broadcasts for the
IP sub-net, IPX network, or AppleTalk cable range to all ports within the IP sub-net, IPX network, or AppleTalk
cable VLAN at Layer 2.
The Layer 3 Switch routes packets between VLANs at Layer 3. To configure an IP sub-net, IPX network, or
AppleTalk cable VLAN to route, you must add a virtual routing interface to the VLAN, then configure the
appropriate routing parameters on the virtual routing interface.
NOTE:
The Layer 3 Switch routes packets between VLANs of the same protocol. The Layer 3 Switch cannot
route from one protocol to another.
Summary of Contents for FastIron Edge Switch X424
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