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LAN Switching Configuration Guide, Cisco IOS Release 12.4T
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Configuring IP Multicast Multilayer Switching
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Contents
Configuring IP Multicast Multilayer SwitchingLast Updated: December 8, 2011
This module describes how to configure IP multicast Multilayer Switching (MLS).
Finding Feature InformationYour software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Prerequisites for Configuring IP Multicast Multilayer SwitchingThe following prerequisites are necessary before IP multicast MLS can function:
Restrictions for Configuring IP Multicast Multilayer SwitchingThe restrictions in the following sections apply to IP multicast MLS on the router:
Router Configuration Restrictions for IP Multicast Multilayer SwitchingIP multicast MLS does not work on internal or external routers in the following situations:
External Router Guidelines for IP Multicast Multilayer SwitchingFollow these guidelines when using an external router:
Access List Restrictions and Guidelines for IP Multicast Multilayer SwitchingThe following restrictions apply when using access lists on interfaces participating in IP multicast MLS:
For example, if the following input access list is applied to the RPF interface for a group of flows, no flows will be multilayer switched even though the second entry permits all IP traffic (because the protocol specified in the first entry is not ip): Router(config)# access-list 101 permit udp any any Router(config)# access-list 101 permit ip any any If the following input access list is applied to the RPF interface for a group of flows, all flows except the {s1, g1} flow are multilayer switched (because the protocol specified in the entry for {s1, g1} is not ip): Router(config)# access-list 101 permit udp s1 g1 Router(config)# access-list 101 permit ip any any Information About IP Multicast Multilayer SwitchingThe IP multicast MLS feature provides high-performance, hardware-based, Layer 3 switching of IP multicast traffic for routers connected to LAN switches. An IP multicast flow is a unidirectional sequence of packets between a multicast source and the members of a destination multicast group. Flows are based on the IP address of the source device and the destination IP multicast group address. IP multicast MLS switches IP multicast data packet flows between IP subnets using advanced, ASIC switching hardware, thereby off loading processor-intensive, multicast packet routing from network routers. The packet forwarding function is moved onto the connected Layer 3 switch whenever a supported path exists between a source and members of a multicast group. Packets that do not have a supported path to reach their destinations are still forwarded in software by routers. Protocol Independent Multicast (PIM) is used for route determination. For conceptual information about IP Multicast Multilayer Switching, see the "Multilayer Switching Overview" module. How to Configure and Monitor IP Multicast Multilayer SwitchingTo configure your Cisco router for IP multicast MLS, perform the tasks described in the following sections. The first two sections contain required tasks; the remaining tasks are optional.
Enabling IP Multicast RoutingYou must enable IP multicast routing globally on the MMLS-RPs before you can enable IP multicast MLS on router interfaces. To enable IP multicast routing on the router, complete the following steps. DETAILED STEPS
Enabling IP PIMYou must enable IP PIM on the router interfaces connected to the switch before IP multicast MLS will function on those router interfaces. To enable IP PIM, complete the following steps. DETAILED STEPS
Reenabling IP Multicast MLSIP multicast MLS is enabled by default when you enable IP PIM on the interface. Perform this task only if you disabled IP multicast MLS and you want to reenable it. To reenable IP multicast MLS on an interface, complete the following steps. DETAILED STEPS Specifying an IP Multicast MLS Management InterfaceWhen you enable IP multicast MLS, the subinterface (or VLAN interface) that has the lowest VLAN ID and is active (in the "up" state) is automatically selected as the management interface. The one-hop protocol Multilayer Switching Protocol (MLSP) is used between a router and a switch to pass messages about hardware-switched flows. MLSP packets are sent and received on the management interface. Typically, the interface in VLAN 1 is chosen (if that interface exists). Only one management interface is allowed on a single trunk link. In most cases, we recommend that the management interface be determined by default. However, you can optionally specify a different router interface or subinterface as the management interface. We recommend using a subinterface with minimal data traffic so that multicast MLSP packets can be sent and received more quickly. If the user-configured management interface goes down, the router uses the default interface (the active interface with the lowest VLAN ID) until the user-configured interface comes up again. To specify the IP multicast MLS management interface, complete the following steps. DETAILED STEPS Monitoring and Maintaining an IP Multicast MLS NetworkTo monitor and maintain an IP multicast MLS network, use one or more of the show commands listed below. DETAILED STEPS IP Multicast MLS Configuration ExamplesThis section contains the following examples:
Basic IP Multicast MLS Network Examples
Network Topology ExampleThe figure below shows a basic IP multicast MLS example network topology. The network is configured as follows:
Operation Before IP Multicast MLS ExampleWithout IP multicast MLS, when the G1 source (on VLAN 10) sends traffic destined for IP multicast group G1, the switch forwards the traffic (based on the Layer 2 multicast forwarding table entry generated by the IGMP snooping, CGMP, or GMRP multicast service) to Host A on VLAN 10 and to the router subinterface in VLAN 10. The router receives the multicast traffic on its incoming subinterface for VLAN 10, checks the multicast routing table, and replicates the traffic to the outgoing subinterfaces for VLANs 20 and 30. The switch receives the traffic on VLANs 20 and 30 and forwards the traffic received on these VLANs to the appropriate switch ports, again based on the contents of the Layer 2 multicast forwarding table. Operation After IP Multicast MLS ExampleAfter IP multicast MLS is implemented, when the G1 source sends traffic destined for multicast group G1, the MMLS-SE checks its Layer 3 multicast MLS cache and recognizes that the traffic belongs to a multicast MLS flow. The MMLS-SE forwards the traffic to Host A on VLAN 10 based on the multicast forwarding table, but does not forward the traffic to the router subinterface in VLAN 10 (assuming a completely switched flow). For each multicast MLS cache entry, the switch maintains a list of outgoing interfaces for the destination IP multicast group. The switch replicates the traffic on the appropriate outgoing interfaces (VLANs 20 and 30) and then forwards the traffic on each VLAN to the destination hosts (using the Layer 2 multicast forwarding table). The switch performs a packet rewrite for the replicated traffic so that the packets appear to have been routed by the appropriate router subinterface. If not all the router subinterfaces are eligible to participate in IP multicast MLS, the switch must forward the multicast traffic to the router subinterface in the source VLAN (in this case, VLAN 10). In this situation, on those subinterfaces that are ineligible, the router performs multicast forwarding and replication in software, in the usual manner. On those subinterfaces that are eligible, the switch performs multilayer switching. Router Configuration ExampleThe following is an example configuration of IP multicast MLS on the router: ip multicast-routing interface fastethernet2/0.10 encapsulation isl 10 ip address 10.1.10.1 255.255.255.0 ip pim dense-mode interface fastethernet2/0.20 encapsulation isl 20 ip address 10.1.20.1 255.255.255.0 ip pim dense-mode interface fastethernet2/0.30 encapsulation isl 30 ip address 10.1.30.1 255.255.255.0 ip pim dense-mode mls rp ip multicast management-interface You will receive the following message informing you that you changed the management interface: Warning: MLS Multicast management interface is now Fa2/0.30 Switch Configuration ExampleThe following example shows how to configure the switch (MMLS-SE): Console> (enable) set trunk 1/2 on isl Port(s) 1/2 trunk mode set to on. Port(s) 1/2 trunk type set to isl. Console> (enable) set igmp enable IGMP feature for IP multicast enabled Console> (enable) set mls multicast enable Multilayer Switching for Multicast is enabled for this device. Console> (enable) set mls multicast include 10.1.10.1 Multilayer switching for multicast is enabled for router 10.1.10.1. Complex IP Multicast MLS Network Examples
Network Topology ExampleThe figure below shows a more complex IP multicast MLS example network topology. The network is configured as follows:
Operation Before IP Multicast MLS ExampleWithout IP multicast MLS, when Server A (on VLAN 10) sends traffic destined for IP multicast group G1, Switch B forwards the traffic (based on the Layer 2 multicast forwarding table entry) to Host A on VLAN 10 and to Switch A. Switch A forwards the traffic to the Router A and Router B subinterfaces in VLAN 10. Router A receives the multicast traffic on its incoming subinterface for VLAN 10, checks the multicast routing table, and replicates the traffic to the outgoing subinterface for VLAN 20. Router B receives the multicast traffic on its incoming interface for VLAN 10, checks the multicast routing table, and replicates the traffic to the outgoing subinterface for VLAN 30. Switch A receives the traffic on VLANs 20 and 30. Switch A forwards VLAN 20 traffic to the appropriate switch ports (in this case, to Host C), based on the contents of the Layer 2 multicast forwarding table. Switch A forwards the VLAN 30 traffic to Switch C. Switch C receives the VLAN 30 traffic and forwards it to the appropriate switch ports (in this case, Hosts D and E) using the multicast forwarding table. Operation After IP Multicast MLS ExampleAfter IP multicast MLS is implemented, when Server A sends traffic destined for multicast group G1, Switch B forwards the traffic (based on the Layer 2 multicast forwarding table entry) to Host A on VLAN 10 and to Switch A. Switch A checks its Layer 3 multicast MLS cache and recognizes that the traffic belongs to a multicast MLS flow. Switch A does not forward the traffic to the router subinterfaces in VLAN 10 (assuming a completely switched flow). Instead, Switch A replicates the traffic on the appropriate outgoing interfaces (VLANs 20 and 30). VLAN 20 traffic is forwarded to Host C and VLAN 30 traffic is forwarded to Switch C (based on the contents of the Layer 2 multicast forwarding table). The switch performs a packet rewrite for the replicated traffic so that the packets appear to have been routed by the appropriate router subinterface. Switch C receives the VLAN 30 traffic and forwards it to the appropriate switch ports (in this case, Hosts D and E) using the multicast forwarding table. If not all the router subinterfaces are eligible to participate in IP multicast MLS, the switch must forward the multicast traffic to the router subinterfaces in the source VLAN (in this case, VLAN 10). In this situation, on those subinterfaces that are ineligible, the routers perform multicast forwarding and replication in software in the usual manner. On those subinterfaces that are eligible, the switch performs multilayer switching.
Router A (MMLS-RP) Configurationip multicast-routing interface fastethernet1/0.1 encapsulation isl 1 ip address 172.20.1.1 255.255.255.0 interface fastethernet1/0.10 encapsulation isl 10 ip address 172.20.10.1 255.255.255.0 ip pim dense-mode interface fastethernet1/0.20 encapsulation isl 20 ip address 172.20.20.1 255.255.255.0 ip pim dense-mode Router B (MMLS-RP) Configurationip multicast-routing interface fastethernet1/0.1 encapsulation isl 1 ip address 172.20.1.2 255.255.255.0 interface fastethernet2/0.10 encapsulation isl 10 ip address 172.20.10.100 255.255.255.0 ip pim dense-mode interface fastethernet2/0.30 encapsulation isl 30 ip address 172.20.30.100 255.255.255.0 ip pim dense-mode Switch A (MMLS-SE) ConfigurationConsole> (enable) set vlan 10 Vlan 10 configuration successful Console> (enable) set vlan 20 Vlan 20 configuration successful Console> (enable) set vlan 30 Vlan 30 configuration successful Console> (enable) set trunk 1/1 on isl Port(s) 1/1 trunk mode set to on. Port(s) 1/1 trunk type set to isl. Console> (enable) set trunk 1/2 on isl Port(s) 1/2 trunk mode set to on. Port(s) 1/2 trunk type set to isl. Console> (enable) set trunk 1/3 desirable isl Port(s) 1/3 trunk mode set to desirable. Port(s) 1/3 trunk type set to isl. Console> (enable) set trunk 1/4 desirable isl Port(s) 1/4 trunk mode set to desirable. Port(s) 1/4 trunk type set to isl. Console> (enable) set igmp enable IGMP feature for IP multicast enabled Console> (enable) set mls multicast enable Multilayer Switching for Multicast is enabled for this device. Console> (enable) set mls multicast include 172.20.10.1 Multilayer switching for multicast is enabled for router 172.20.10.1. Console> (enable) set mls multicast include 172.20.10.100 Multilayer switching for multicast is enabled for router 172.20.10.100. Console> (enable) Additional ReferencesRelated Documents
MIBsTechnical Assistance
Feature Information for Configuring IP Multicast Multilayer SwitchingThe following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R) Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. © 2011 Cisco Systems, Inc. All rights reserved.
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