Foundry Networks Switch and Router Installation And Configuration Manual page 949

Routing Between VLANs using Virtual Interfaces (routers only)
Foundry Layer 3 Switches offer the ability to create a virtual interface within a Layer 2 STP port-based VLAN or
within each Layer 3 protocol, IP sub-net, or IPX network VLAN. This combination of multiple Layer 2 and/or
Layer 3 broadcast domains and virtual interfaces are the basis for Foundry Networks' very powerful Integrated
Switch Routing (ISR) technology. ISR is very flexible and can solve many networking problems. The following
example is meant to provide ideas by demonstrating some of the concepts of ISR.
Example: Suppose you want to move routing out to each of three buildings in a network. Remember that the only
protocols present on VLAN 2 and VLAN 3 are IP and IPX. Therefore, you can eliminate tagged ports 25 and 26
from both VLAN 2 and VLAN 3 and create new tagged port-based VLANs to support separate IP sub-nets and
IPX networks for each backbone link.
You also need to create unique IP sub-nets and IPX networks within VLAN 2 and VLAN 3 at each building. This
will create a fully routed IP and IPX backbone for VLAN 2 and VLAN 3. However, VLAN 4 has no protocol
restrictions across the backbone. In fact there are requirements for NetBIOS and DecNet to be bridged among the
three building locations. The IP sub-net and IPX network that exists within VLAN 4 must remain a flat Layer 2
switched STP domain. You enable routing for IP and IPX on a virtual interface only on NetIron-A. This will provide
the flat IP and IPX segment with connectivity to the rest of the network. Within VLAN 4 IP and IPX will follow the
STP topology. All other IP sub-nets and IPX networks will be fully routed and have use of all paths at all times
during normal operation.
Figure 25.15 shows the configuration described above.
Building 1
NetIron-A
FastIron Workgroup
1 3 5 7 9 11 13 15
Link Link
Activity Activity 2 4 6 8 10 12 14 16
Console FDX FDX
100 100
Link / Act Link / Act
Power FDX FDX
100 100
Link / Act Link / Act
Vlan2 Vlan8 Vlan 3 Vlan 4
Figure 25.15 Routing between protocol-based VLANs
To configure the Layer 3 VLANs and virtual interfaces on the NetIron routers in Figure 25.15, use the following
procedure.
December 2000
17 19 21 23
V5 IP/IPX V4 18 20 22 24 V5 IP/IPX V4
FDX
100
Link / Act
FDX
100
Link / Act
FastIron Workgroup
1 3
Link Link
V6 IP/IPX V4 2 4
Activity Activity
FDX
Console
100
Link / Act
Power FDX
100
Link / Act
Vlan2 Vlan8 Vlan 3
Building 3
NetIron-C
V5 IP/IPX V4
5 7 9 11 13 15 17 19 21 23
6 8 10 12 14 16 V7 IP/IPX V4 18 20 22 24
FDX FDX
100 100
Link / Act Link / Act
FDX FDX
100 100
Link / Act Link / Act
Vlan 4
Configuring Virtual LANs (VLANs)
Building 2
NetIron-B
FastIron Workgroup
1 3 5 7 9 11 13 15 17
Link Link
Activity Activity 2 4 6 8 10 12 14 16 18
Console FDX FDX FDX
100 100 100
Link / Act Link / Act Link / Act
Power FDX FDX FDX
100 100 100
Link / Act Link / Act Link / Act
Vlan2 Vlan8 Vlan 3 Vlan 4
= STP Blocked VLAN
19 21 23
20 22 24
25 - 29