6.2 Route Switch Modules
6.2.4 Configure RSM interfaces
Configuring inter-VLAN routing on the RSM consists of two main procedures:
  • Creating and configuring VLANs on the switch and assigning VLAN membership to switch ports.
  • Creating and configuring VLAN interfaces for inter-VLAN routing on the RSM; a VLAN interface must be configured for each VLAN with traffic to be routed.

As previously discussed, VLANs are created at the switch level as a means of grouping ports. However, VLANs are controlled at the route-processor level. VLAN interfaces on the RSM are virtual interfaces, but you configure them much as you do a physical router interface. To specify a VLAN interface on the RSM of a Catalyst 5000 Series Switch, enter the following command in global configuration mode:

Router(config)#interface vlan vlan-interface -number

To specify a VLAN interface other than VLANs 0 and 1, use the VLAN number as the vlan-interface-number. The interface number configured on the Route Processor corresponds to the VLAN number configured on the Catalyst 5000 Series Switch. For example, interface VLAN 100 corresponds to VLAN 100 on the Catalyst 5000 Series Switch. The RSM can route up to 256 VLANs.

After you define the VLAN interface, you must assign a unique IP address to that interface. To assign a unique IP address and subnet mask to an interface, enter the following command in interface configuration mode:

Router(config-if)#ip address ip-address subnet-mask

Each VLAN that the RSM is routing appears as a separate virtual interface. Therefore, the configuration file of the RSM has an interface description for each VLAN.

The RSM on the Catalyst 5000 Series has one global MAC address that applies to all interfaces on that device. Specifying a unique MAC address per interface enhances the operations of the RSM interface when working with some Catalyst Switches. Assigning a unique MAC address per interface has the following benefits:

  • Makes best use of Fast EtherChannel® technology and load distribution because Fast EtherChannel technology uses a portion of the MAC address to determine the link the data uses.
  • Enhances multilayer switching management by providing unique MAC addresses per interface in the Multilayer Switching (MLS) cache.
  • Avoids Catalyst 1900 Switch operation problems by assigning unique MAC addresses in the Cisco 1900 switch content-addressable memory (CAM) table.

The Catalyst 5000 Series set command-based switches are slightly different. The Catalyst 4000 Family Layer 3 engine uses Cisco Express Forwarding (CEF). This technology provides Layer 3 switching based on a topology map of the entire network that is distributed to multiple application-specific integrated circuits (ASICs), allowing autonomous-switching decisions without the involvement of a centralized CPU.

The RSM concept is gone. The Layer 3 module looks like a router, but it is never referred to as an RSM rather a Layer 3 service module. Inter-VLAN traffic is run through the Gigabit Ethernet ports (both on the front panel and on backplane gigabit ports that you can't see). The concept of "interface vlan xxx" from the Catalyst 5000 Series does not apply here. With the Catalyst 5000 Series, you configure subinterfaces on IEEE 802.1q gigabit ports and the subinterfaces are assigned to a VLAN.

Perform the following steps to configure the interfaces as a channel (in this procedure, the Layer 3 services module is in Slot 2):

Step 1 - Use the set port channel mod/ports command to configure a Gigabit EtherChannel. Before you create the channel, ensure that the ports you intend to channel (in this case, 2/1 and 2/2) belong to the same VLAN:

Cat4000> (enable) set port channel 2/1-2 on
Ports 2/1-2 channel mode set to on.
Cat4000> (enable)

Step 2 - Use the set trunk mod_num/port_num command to enable trunking and specify an encapsulation type on the EtherChannel ports (specifying the encapsulation type on one of the EtherChannel ports enables trunking and the specified encapsulation on all ports in the channel):

Cat4000> (enable) set trunk 2/1 on dot1Q 1-10
Port(s) 2/1 trunk mode set to on
Port(s) 2/1 trunk type set to dot1Q 1-10
Cat4000> (enable)

Step 3 - Use the session mod_num command to access the Layer 3 services module console prompt:

Cat4000> (enable) session 2
Trying Router...
Connected to Router.
Escape character is \Q^]'.

router>

a. At the EXEC prompt, enter enable mode:

router> enable
router#

b. At the privileged EXEC prompt, enter global configuration mode:

router#configure terminal
router(config)#

Step 4 - Create an EtherChannel (portchannel) interface (the channel number can be from
1 to 64):

router(config)#interface port-channel channel_number

Step 5 - Assign the g3 and g4 interfaces to the port channel:

router(config)#interface g3
router(config-if)#channel-group channel_number
router(config-if)#exit
router(config)#

Repeat this step on the g4 interface.

Step 6 - Configure subinterfaces on the port channel interface, one for each allowed VLAN configured on the Layer 3 service module trunk over which you want to route (specify the same type of encapsulation as in Step 2):

router(config)#interface port-channel channel_number.vlan_id
router(config-subif)#encapsulation dot1Q vlan_id
router(config-subif)#ip address ip_address subnet_mask
router(config-subif)#exit

Repeat this step to create and configure additional subinterfaces on the port channel.

Step 7 - Configure a subinterface for the native VLAN by specifying the native keyword in the encapsulation command:

router(config)#interface port-channel channel_number.vlan_id
router(config-subif)#encapsulation dot1Q vlan_id native
router(config-subif)#ip address ip_address subnet_mask
router(config-subif)#exit

The example in Figures illustrate a sample configuration on a Catalyst 5500 Series Switch.

The example in Figures and illustrate a sample configuration on a Catalyst 4000 Series Switch.

Lab Activity
  In this lab activity, you will learn how to configure routing between RSM and an external router connected to an ISP.