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This chapter describes how to configure your network to perform IP multicast Multilayer Switching (MLS). For a complete description of the Multilayer Switching commands, see the chapter "IP Multicast MLS Commands" in the Cisco IOS Switching Services Command Reference. For documentation of other commands that appear in this chapter, you can use the command reference master index or search online.
This chapter contains these sections:
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Note The information in this chapter is a brief summary of the information contained in the Catalyst 5000 Series Multilayer Switching User Guide. The commands and configurations described in this guide apply only to the devices that provide routing services. Commands and configurations for Catalyst 5000 series switches are documented in the Catalyst 5000 Series Multilayer Switching User Guide. |
The following prerequisites are necessary before MLS can function:
You must also configure the Catalyst 5000 series switch in order for IP multicast MLS to function on the router.
The restrictions in the following sections apply to IP multicast MLS on the router:
IP multicast MLS does not work on internal or external routers in the following situations:
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Note Groups in the 224.0.0.* range are reserved for routing control packets and must be flooded to all forwarding ports of the VLAN. These addresses map to the multicast MAC address range 01-00-5E-00-00-xx, where xx is in the range 0 to 0xFF. |
Follow these guidelines when using an external router:
The following restrictions apply when using access lists on interfaces participating in IP multicast MLS:
Router(config)# access-list 101 permit udp any any Router(config)# access-list 101 permit ip any any
Router(config)# access-list 101 permit udp s1 g1 Router(config)# access-list 101 permit ip any any
Perform the tasks in this section to configure your Cisco router for IP multicast MLS. To ensure a successful multicast MLS configuration, you must also configure the Catalyst Switches in your network. For a full description, see the Catalyst 5000 Series Multilayer Switching User Guide. Only configuration tasks and commands for routers are described in this chapter.
For examples of IP multicast MLS configurations, see the "IP Multicast MLS Configuration Examples" section later in this document.
You 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, use the following command in router configuration mode:
| Command | Purpose |
|---|---|
Router(config)# ip multicast-routing | Enables IP multicast routing globally. |
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NoteThis section describes only how to enable IP multicast routing on the router. For detailed IP multicast configuration information, refer to the "Configuring IP Multicast Routing" chapter in the Cisco IOS IP and IP Routing Configuration Guide. |
You must enable Protocol Independent Multicast (PIM) on the router interfaces connected to the switch before IP multicast MLS will function on those router interfaces. To do so, use the following commands in interface configuration mode:
| Command | Purpose | |
|---|---|---|
Step1 | Router(config)# interface type number | Configures an interface. |
Step2 | Router(config-if)# ip pim {dense-mode | sparse-mode
| sparse-dense-mode}
| Enables PIM on the interface. |
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NoteThis section describes only how to enable PIM on router interfaces. For detailed PIM configuration information, refer to the "Configuring IP Multicast Routing" chapter in the Cisco IOS IP and IP Routing Configuration Guide. |
IP multicast MLS is enabled by default when you enable PIM on the interface. Perform this task only if you disabled IP multicast MLS and you want to reenable it. To enable IP multicast MLS on an interface, use the following command in interface configuration mode:
| Command | Purpose |
|---|---|
Router(config-if)# mls rp ip multicast |
When 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 VLAN1 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 change the default IP multicast MLS management interface, use the following command in interface configuration mode:
| Command | Purpose |
|---|---|
Router(config-if)# mls rp ip multicast management-interface | Configures an interface as the IP multicast MLS management interface. |
To monitor and maintain an IP multicast MLS network, use the following show commands:
| Command | Purpose |
|---|---|
Router# show ip mroute [group-name | group-address [source]] | Displays hardware switching state for outgoing interfaces. |
Router# show ip pim interface [type number] [count] | Displays PIM interface information. |
Router# show mls rp ip multicast [locate] [group [source] [vlan-id]] | [statistics] | [summary] | Displays Layer 3 switching information. |
The following sections contain example IP multicast MLS implementations. These examples include the switch configurations, although switch commands are not documented in this router publication. Refer to the Catalyst 5000 Command Reference for that information.
This example consists of the following sections:
Figure 32 shows a basic IP multicast MLS example network topology.
The network is configured as follows:
Without 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 Layer2 multicast forwarding table entry generated by the IGMP snooping, CGMP, or GMRP multicast service) to HostA on VLAN10 and to the router subinterface in VLAN10.
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 Layer2 multicast forwarding table.
After IP multicast MLS is implemented, when the G1 source sends traffic destined for multicast group G1, the MMLS-SE checks its Layer3 multicast MLS cache and recognizes that the traffic belongs to a multicast MLS flow. The MMLS-SE forwards the traffic to HostA on VLAN 10 based on the multicast forwarding table, but does not forward the traffic to the router subinterface in VLAN10 (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 Layer2 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, VLAN10). 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.
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NoteOn the MMLS-RP, the IP multicast MLS management interface is user-configured to the VLAN30 subinterface. If this interface goes down, the system will revert to the default management interface (in this case, the VLAN10 subinterface). |
The 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
The 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.
This example consists of the following sections:
Figure 33 shows a more complex IP multicast MLS example network topology.
The network is configured as follows:
Without IP multicast MLS, when ServerA (on VLAN 10) sends traffic destined for IP multicast group G1, SwitchB forwards the traffic (based on the Layer2 multicast forwarding table entry) to HostA on VLAN10 and to SwitchA. Switch A forwards the traffic to the Router A and Router B subinterfaces in VLAN10.
RouterA 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. RouterB 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.
SwitchA receives the traffic on VLANs 20 and 30. SwitchA forwards VLAN 20 traffic to the appropriate switch ports (in this case, to HostC), based on the contents of the Layer2 multicast forwarding table. SwitchA forwards the VLAN 30 traffic to SwitchC.
Switch C receives the VLAN 30 traffic and forwards it to the appropriate switch ports (in this case, HostsD and E) using the multicast forwarding table.
After IP multicast MLS is implemented, when ServerA sends traffic destined for multicast groupG1, SwitchB forwards the traffic (based on the Layer2 multicast forwarding table entry) to HostA on VLAN10 and to SwitchA.
Switch A checks its Layer3 multicast MLS cache and recognizes that the traffic belongs to a multicast MLS flow. SwitchA does not forward the traffic to the router subinterfaces in VLAN 10 (assuming a completely switched flow). Instead, SwitchA 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 Layer2 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, HostsD 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, VLAN10). 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.
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NoteOn both MMLS-RPs, no user-configured IP multicast MLS management interface is specified. Therefore, the VLAN1 subinterface is used by default. |
Router A (MMLS-RP) Configuration
ip 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) Configuration
ip 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) Configuration
Console> (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)
The following example shows how to configure Switch B (assuming VLAN Trunking Protocol [VTP] is used for VLAN management):
Console> (enable) set igmp enable IGMP feature for IP multicast enabled Console> (enable)
The following example shows how to configure Switch C (assuming VTP is used for VLAN management):
Console> (enable) set igmp enable IGMP feature for IP multicast enabled Console> (enable)
Posted: Mon Jul 17 16:54:10 PDT 2000
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