Section 7.3: Configuring Multi-Layer Switching
To process of configuring multilayer switching contains a number of steps. Before you can configure MLS for a specific VLAN or interface, you must globally enable the MLSP that operates between the route processor and the switch. To enable MLSP on the route processor, enter the following command in global configuration mode:
Router(config)#mls rp ip
You can use the no mis rp ip command in global configuration mode to disable MLS on the route processor. In Cisco's implementation of MLS, Layer 3 switches IP and IP multicast packets. Any other packets are routed as in a non-Layer 3 switched network. MLS is a form of interVLAN routing. Multilayer switches make forwarding decisions based upon which ports are configured for which VLANs. Internal route processors and ISL-configured links use VLAN IDs to identify interfaces. External route processor interfaces have knowledge regarding subnets but not VLANs. Therefore, MLS requires that each external route processor interface have a VLAN ID assigned to it. To assign a VLAN ID to a route processor interface, use the following commands in interface configuration mode:
Router (config)#interface interface_number Router (config-if)#mls rp vlan-id vlan_id_number
In the second command, vian-id-number represents the VLAN assigned to the interface specified in the interface_number argument in the interface command.
To remove an interface from a VLAN, use the no mls rp vlan-id vian_id_number command. This removes the VLAN ID from an interface and, in so doing, disables MLS for that interface.
Once you have determined which route processor interfaces will be MLS interfaces, you must add the interfaces to the same VTP domain as the switch. To place an external route processor interface in the same VTP domain as the switch, use the following commands in interface configuration mode:
Router(config) interface interface_nvmber Router(config-if)# mls rp vtp-domain domain_name
For an ISL interface, use the mls rp vtp-domain command only on the primary interface as all subinterfaces that are part of the primary interface inherit the VTP domain of the primary interface.
Use the no mls rp vtp-domain domain_name command to remove the MLS interface from a VTP domain.
You can use the show mls rp vtp-domain domain_name command to see domain information for a specific VTP domain:
Once you have put an interface into a particular VTP domain you must enable MLS. MLS must be enabled on every interface that will participate in Layer 3 switching. On a router or RSM interface, use the following command in interface configuration mode in order to enable MLS:
Router (config-if)#mls rp ip
You can use the no mls rp ip command to disable MLS on an interface.
When a RSM or router is configured to participate in MLS, the device uses the MLSP to send Hello messages, advertise routing changes, and announce the VLANs or MAC addresses of those interfaces on the devices participating in MLS. One interface on the MLS-RP must be identified as the management interface through which MLSP packets are sent and received. The MLSP management interface can be any MLS interface connected to the switch. Only one management interface needs to be specified. If no management interface is configured, however, MLSP messages will not be sent. Multiple interfaces on the same route processor can be configured as a management interface; though this will increase the management overhead per route processor. To identify a management interface on an RSM or router, use the following command in interface configuration mode:
Router(config-if)#mls rp management-interface
You can disable the management interface by using the no mls rp management-interface command in interface configuration mode.
You can use the show mls rp exec command to verify the MLS configuration for an MLS-RP. This command identifies each MLS-RP to the switch by both the MLS ID and MLS IP address of the route processor. The MLS ID is the MAC address of the route processor. The MLS-RP automatically selects the IP address of one of its interfaces and uses that IP address as its MLS IP address.
To verify the MLS configuration for a specific interface, enter the following command in privilege exec mode:
Router#show mls rp interface interface_number
This command displays information that indicates whether MLS is configured on the specified interface; the VTP domain in which the VLAN ID resides; and whether the interface is configured as the management interface for the MLS-RP.