Configuring InterVLAN Routing

Network devices in different VLANs cannot communicate with one another without a router to route traffic between the VLANs. In most network environments, VLANs are associated with individual networks or subnetworks.

For example, in an IP network, each subnetwork is mapped to an individual VLAN. In an IPX network, each VLAN is mapped to an IPX network number.

Configuring VLANs helps control the size of the broadcast domain and keeps local traffic local. However, when an end station in one VLAN needs to communicate with an end station in another VLAN, interVLAN communication is required. This communication is supported by interVLAN routing. You configure one or more routers to route traffic to the appropriate destination VLAN.

Figure 2-1 shows a basic interVLAN routing topology. Switch A is in VLAN 10 and Switch B is in VLAN 20. The router has an interface in each VLAN.

Figure 2-1: Basic InterVLAN Routing Topology

When Host A in VLAN 10 needs to communicate with Host B in VLAN 10, it sends a packet addressed to that host. Switch A forwards the packet directly to Host B, without sending it to the router.

When Host A sends a packet to Host C in VLAN 20, Switch A forwards the packet to the router, which receives the traffic on the VLAN 10 interface. The router checks the routing table, determines the correct outgoing interface, and forwards the packet out the VLAN 20 interface to Switch B. Switch B receives the packet and forwards it to Host C.

Configuring VLAN Trunk Protocol and VLANs on the Switch

To configure the MSFC for interVLAN routing, you must configure VLAN Trunk Protocol (VT P) and create and configure VLANs on the switch.

Note This section describes the basics of VTP and VLAN configuration. For mo re information, refer to the Catalyst 6000 Family Software Configuration Guide.

Note You must have an active VLAN on the switch before the MSFC will bring that VLAN interface up.

Note The MSFC can be con figured with up to 256 VLAN interfaces.

To configure VTP and VLANs on the switch, perform this task in privileged mode:

Task Command

Step 1 Specify the VTP mode.

set vtp mode {client | server | transparent}

Step 2 Configure a VTP domain (if you configured the switch as a VTP client or server).

set vtp domain name

Step 3 Create VLANs on the switch.

set vlan vlan_num

Step 4 Assign ports to the VLAN.

set vlan vlan_num mod_num/port_num

Task	Command
Step 1 Specify the VTP mode.	set vtp mode {client \| server \| transparent}
Step 2 Configure a VTP domain (if you configured the switch as a VTP client or server).	set vtp domain name
Step 3 Create VLANs on the switch.	set vlan vlan_num
Step 4 Assign ports to the VLAN.	set vlan vlan_num mod_num/port_num

This example shows how to configure VTP, create two VLANs, and assign switch ports to those VLANs:

Console> (enable) set vtp mode server
VTP domain modified
Console> (enable) set vtp domain Corp_Net
VTP domain Corp_Net modified
Console> (enable) set vlan 100
Vlan 100 configuration successful
Console> (enable) set vlan 200
Vlan 200 configuration successful
Console> (enable) set vlan 100 3/1-12
VLAN 100 modified.
VLAN 1 modified.
VLAN  Mod/Ports
---- -----------------------
100   1/1-2
      3/1-12
 
Console> (enable) set vlan 200 3/13-24
VLAN 200 modified.
VLAN 1 modified.
VLAN  Mod/Ports
---- -----------------------
200   1/1-2
      3/13-24
 
Console> (enable)

Basic Router Config uration Tasks

These sections describe basic router configuration tasks you need to understand before you configure interVLAN routing:

Accessing the MSFC from the Switch

These sections describe how to access the MSFC from a directly connected console port or from a Telnet session:

Accessing the MSFC from the Co nsole Port

You can use the switch console command to access the MSFC from the switch command-line interface (CLI) directly connected to the supervisor engine console port. To exit from the router CLI and return to the switch CLI, enter ^C^C^C at the Router> prompt.

To access the MSFC from the switch command-line interface, perform this task:

Task Command

Access the MSFC from the switch CLI.

Console> (enable) switch console [mod_num]¹

¹The mod_num keyword specifies the module number of the MSFC; either 15 (if the MSFC is installed on the supervisor in slot 1) or 16 (if in slot 2). If no module number is specified, the console will switch to the MSFC on the active supervisor.

Task	Command
Access the MSFC from the switch CLI.	Console> (enable) switch console [mod_num]¹

Note To access the router CLI on the standby MSFC, connect to the console port of the standby supervisor engine.

This example shows how to access the active MSFC from the switch CLI from the active supervisor engine, and how to exit the router CLI and return to the switch CLI:

Console> (enable) switch console 15
Trying Router-15...
Connected to Router-15.
Type ^C^C^C to switch back...
Router>^C^C^C
Console> (enable)

Accessing the MSFC fro m a Telnet Session

You can use the session mod_num command to access the MSFC from the switch CLI using a Telnet session. To exit from the router CLI back to the switch CLI, enter the exit command at the Router> prompt.

Note The supervisor engine software sees the MSFC as module 15 (when installed on a supervisor engine in slot 1) or module 16 (when installed on a supervisor engine in slot 2).

This example shows how to access the MSFC from the switch CLI, and how to exit the router CLI and return to the switch CLI:

Console> (enable) session 15
Router> exit
Console> (enable)

Accessing Configuration Mode on the Ro uter

To access configuration mode on the router, perform this task:

Note Enter the switch console command to access the MSFC from the switch CLI when directly connected to the supervisor engine console port. To access the MSFC from a Telnet session, see "Accessing the MSFC from a Telnet Session" section.

Task Command

Step 1 If you are in the switch CLI, enter the router CLI.

Console> switch console [mod_num]

Step 2 At the EXEC prompt, enter enable mode.

Router> enable

Step 3 At the privileged EXEC prompt, enter global configuration mode.

Router# configure terminal

Step 4 Enter the commands to configure interVLAN routing.

(Refer to the appropriate configuration tasks later in this chapter.)

Step 5 Exit configuration mode.

Router(config)# Ctrl-Z

Task	Command
Step 1 If you are in the switch CLI, enter the router CLI.	Console> switch console [mod_num]
Step 2 At the EXEC prompt, enter enable mode.	Router> enable
Step 3 At the privileged EXEC prompt, enter global configuration mode.	Router# configure terminal
Step 4 Enter the commands to configure interVLAN routing.	(Refer to the appropriate configuration tasks later in this chapter.)
Step 5 Exit configuration mode.	Router(config)# Ctrl-Z

Viewing and Saving the Router Conf iguration

To view and save the configuration after you make changes, perform this task:

Task Command

Step 1 View the current operating configuration at the privileged EXEC prompt.

Router# show running-config

Step 2 View the configuration in NVRAM.

Router# show startup-config

Step 3 Save the current configuration to NVRAM.

Router# copy running-config startup-config

Task	Command
Step 1 View the current operating configuration at the privileged EXEC prompt.	Router# show running-config
Step 2 View the configuration in NVRAM.	Router# show startup-config
Step 3 Save the current configuration to NVRAM.	Router# copy running-config startup-config

Bringing Up a Router Inter face

In some cases, a router interface might be administratively shutdown. You can check the status of an interface using the show interface command.

Note In a redundant supervisor engine setup, if an interface on one MSFC is shutdown, the matching VLAN interface on the redundant MSFC will stop forwarding packets. Therefore, you should manually shut down the matching interface on the redundant MSFC.

To bring up a router interface that is administratively shutdown, perform this task in privileged mode:

Task Command

Step 1 Specify the interface to bring up.

Router(config)# interface interface_type interface_number

Step 2 Bring the interface up.

Router(config-if)# no shutdown

Step 3 Exit configuration mode.

Router(config-if)# Ctrl-Z

Task	Command
Step 1 Specify the interface to bring up.	Router(config)# interface interface_type interface_number
Step 2 Bring the interface up.	Router(config-if)# no shutdown
Step 3 Exit configuration mode.	Router(config-if)# Ctrl-Z

Configuring InterVLAN Routing on the MSFC

Note This section is for users who are familiar with Cisco IOS software and have some experience configuring Cisco routers. If you are not familiar with configuring Cisco routers, refer to the documentation for your router platform.

These sections describe how to configure interVLAN routing on the MSFC:

MSFC Configuration Guidelines

Configuring interVLAN routing on the MSFC consists of two main procedures:

1. You must create and configure VLANs on the switch and assign VLAN membership to switch ports. For more information, see the "Configuring VLAN Trunk Protocol and VLANs on the Switch" section.

2. You must create and configure VLAN interfaces for interVLAN routing on the MSFC. You must configure a VLAN interface between each VLAN you want to route traffic.

VLAN interfaces on the MSFC are virtual interfaces. However, you configure them much as you do a physical router interface.

Configuring IP InterVLAN Rou ting on the MSFC

To configure interVLAN routing for IP, perform this task:

Task Command

Step 1 (Optional) Enable IP routing on the router¹.

Router(config)# ip routing

Step 2 (Optional) Specify an IP routing protocol².

Router(config)# router ip_routing_protocol

Step 3 Specify a VLAN interface on the MSFC.

Router(config)# interface vlan-id

Step 4 Assign an IP address to the VLAN.

Router(config-if)# ip address n.n.n.n mask

Step 5 Exit configuration mode.

Router(config-if)# Ctrl-Z

¹This step is necessary if you have multiple routers in the network.
²This step is necessary if you enabled IP routing in Step 1. This step might include other commands, such as using the network router configuration command to specify the networks to route. Refer to the documentation for your router platform for detailed information on configuring routing protocols.

Task	Command
Step 1 (Optional) Enable IP routing on the router¹.	Router(config)# ip routing
Step 2 (Optional) Specify an IP routing protocol².	Router(config)# router ip_routing_protocol
Step 3 Specify a VLAN interface on the MSFC.	Router(config)# interface vlan-id
Step 4 Assign an IP address to the VLAN.	Router(config-if)# ip address n.n.n.n mask
Step 5 Exit configuration mode.	Router(config-if)# Ctrl-Z

This example shows how to enable IP routing on the MSFC, create a VLAN interface, and assign the interface an IP address:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# ip routing
Router(config)# router rip
Router(config-router)# network 10.0.0.0
Router(config-router)# interface vlan 100
Router(config-if)# ip address 10.1.1.1 255.0.0.0
Router(config-if)# ^Z
Router#

Configuring IPX InterV LAN Routing on the MSFC

To configure interVLAN routing for Internetwork Packet Exchange (IPX), perform this task:

Task Command

Step 1 (Optional) Enable IPX routing on the router¹.

Router(config)# ipx routing

Step 2 (Optional) Specify an IPX routing protocol².

Router(config)# ipx router ipx_routing_protocol

Step 3 Specify a VLAN interface on the MSFC.

Router(config)# interface vlan-id

Step 4 Assign a network number to the VLAN³.

Router(config-if)# ipx network [network | unnumbered] encapsulation encapsulation-type

Step 5 Exit configuration mode.

Router(config-if)# Ctrl-Z

¹This step is necessary if you have multiple routers in the network.
²This step is necessary if you enabled IPX routing in Step 1. This step might include other commands, such as using the network router configuration command to specify the networks to route. Refer to the documentation for your router platform for detailed information on configuring routing protocols.
³This enables IPX routing on the VLAN. When you enable IPX routing on the VLAN, you can also specify an encapsulation type.

Task	Command
Step 1 (Optional) Enable IPX routing on the router¹.	Router(config)# ipx routing
Step 2 (Optional) Specify an IPX routing protocol².	Router(config)# ipx router ipx_routing_protocol
Step 3 Specify a VLAN interface on the MSFC.	Router(config)# interface vlan-id
Step 4 Assign a network number to the VLAN³.	Router(config-if)# ipx network [network \| unnumbered] encapsulation encapsulation-type
Step 5 Exit configuration mode.	Router(config-if)# Ctrl-Z

This example shows how to enable IPX routing on the MSFC, create a VLAN interface, and assign the interface an IPX network address:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# ipx routing
Router(config)# ipx router rip
Router(config-ipx-router)# network all
Router(config-ipx-router)# interface vlan100
Router(config-if)# ipx network 100 encapsulation snap
Router(config-if)# ^Z
Router#

Configuring App leTalk InterVLAN Routing on the MSFC

To configure interVLAN routing for AppleTalk, perform this task:

Task Command

Step 1 (Optional) Enable AppleTalk routing on the router¹.

Router(config)# appletalk routing

Step 2 Specify a VLAN interface on the MSFC.

Router(config)# interface vlan-id

Step 3 Assign a cable range to the VLAN.

Router(config-if)# appletalk cable-range cable-range

Step 4 Assign a zone name to the VLAN.

Router(config-if)# appletalk zone zone-name

Step 5 Exit configuration mode.

Router(config-if)# Ctrl-Z

¹This step is necessary if you have multiple routers in the network.

Task	Command
Step 1 (Optional) Enable AppleTalk routing on the router¹.	Router(config)# appletalk routing
Step 2 Specify a VLAN interface on the MSFC.	Router(config)# interface vlan-id
Step 3 Assign a cable range to the VLAN.	Router(config-if)# appletalk cable-range cable-range
Step 4 Assign a zone name to the VLAN.	Router(config-if)# appletalk zone zone-name
Step 5 Exit configuration mode.	Router(config-if)# Ctrl-Z

This example shows how to enable AppleTalk routing on the MSFC, create a VLAN interface, and assign the interface an AppleTalk cable-range and zone name:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# appletalk routing
Router(config)# interface vlan100
Router(config-if)# appletalk cable-range 100-100
Router(config-if)# appletalk zone Engineering
Router(config-if)# ^Z
Router#

Configuring Redunda ncy with HS RP

You can configure one or more Hot Standby Routing Protocol (HSRP) groups on MSFC VLAN interfaces to provide automatic routing backup for your network. Each VLAN interface in an HSRP group shares a virtual IP address and MAC address. You can configure end stations and other devices to use the HSRP address as the default gateway so that if one router interface fails, service is not interrupted to those devices.

The interface with the highest HSRP priority is the active interface for that HSRP group.

To use HSRP, you must have one of the following configurations:

Two supervisor engines in a single chassis (redundant supervisor engines)---Each supervisor engine must be equipped with an MSFC and PFC.
Two supervisor engines in two chassis---You must have one supervisor engine, equipped with an MSFC and PFC, in each chassis.

To configure HSRP on an MSFC VLAN interface, perform this task in interface configuration mode:

Task Command

Step 1 Enable HSRP and specify the HSRP IP address. If you do not specify a group-number, group 0 is used.

Router(config-if)# standby [group-number] ip [ip-address]

Step 2 Specify the priority for the HSRP interface. Increase the priority of at least one interface in the HSRP group (the default is 100). The interface with the highest priority becomes active for that HSRP group.

Router(config-if)# standby [group-number] priority priority

Step 3 (Optional) Configure the interface to preempt the current active HSRP interface and become active if the interface priority is higher than the priority of the current active interface.

Router(config-if)# standby [group-number] preempt [delay delay]

Step 4 (Optional) Set the HSRP hello timer and holdtime timer for the interface. The default values are 3 (hello) and 10 (holdtime). All interfaces in the HSRP group should use the same timer values.

Router(config-if)# standby [group-number] timers hellotime holdtime

Step 5 (Optional) Specify a clear-text HSRP authentication string for the interface. All interfaces in the HSRP group should use the same authentication string.

Router(config-if)# standby [group-number] authentication string

Task	Command
Step 1 Enable HSRP and specify the HSRP IP address. If you do not specify a group-number, group 0 is used.	Router(config-if)# standby [group-number] ip [ip-address]
Step 2 Specify the priority for the HSRP interface. Increase the priority of at least one interface in the HSRP group (the default is 100). The interface with the highest priority becomes active for that HSRP group.	Router(config-if)# standby [group-number] priority priority
Step 3 (Optional) Configure the interface to preempt the current active HSRP interface and become active if the interface priority is higher than the priority of the current active interface.	Router(config-if)# standby [group-number] preempt [delay delay]
Step 4 (Optional) Set the HSRP hello timer and holdtime timer for the interface. The default values are 3 (hello) and 10 (holdtime). All interfaces in the HSRP group should use the same timer values.	Router(config-if)# standby [group-number] timers hellotime holdtime
Step 5 (Optional) Specify a clear-text HSRP authentication string for the interface. All interfaces in the HSRP group should use the same authentication string.	Router(config-if)# standby [group-number] authentication string

This example shows how to configure an interface as part of HSRP group 100:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# interface vlan100
Router(config-if)# standby 100 ip 172.20.100.10
Router(config-if)# standby 100 priority 110
Router(config-if)# standby 100 preempt
Router(config-if)# standby 100 timers 5 15
Router(config-if)# standby 100 authentication Secret
Router(config-if)# ^Z
Router#

Table of Contents

Configuring InterVLAN Routing