Configuring Multicast Routing over GRE Tunnel

Prerequisites for Configuring Multicast Routing over GRE Tunnel

Before configuring multicast routing over GRE, you should be familiar with the concepts of IP Multicast Routing Technology and GRE Tunneling.

Restrictions for Configuring Multicast Routing over GRE Tunnel

The following are the restrictions for configuring multicast routing over GRE tunnel:

  • IPv6 multicast over GRE tunnel is not supported.

  • The total number of supported multicast routes (mroutes) is 32000, across all tunnels.

    Use the formula 8000/(((Number of tunnels)/4) + 1) to derive the number of mroutes.

  • Bidirectional PIM is not supported.

  • Multicast routing should be configured on the first hop router (FHR), the rendezvous point (RP) and the last hop router (LHR) to support multicast over the GRE tunnel.

  • On Catalyst series switches, the tunnel source can be a loopback, physical, or L3 EtherChannel interface.

  • No feature interactions such as IPSec, ACL, Tunnel counters, Crypto support, Fragmentation, Cisco Discovery Protocol (CDP), QoS, GRE keepalive, Multipoint GRE, etc. are supported on the GRE Tunnel.

Information About Multicast Routing over GRE Tunnel

This chapter describes how to configure a Generic Route Encapsulation (GRE) tunnel to tunnel IP multicast packets between non-IP multicast areas. The benefit is that IP multicast traffic can be sent from a source to a multicast group, over an area where IP multicast is not supported. Multicast Routing over GRE Tunnel supports sparse mode and pim-ssm mode; and supports static RP and auto-RP. See Rendevous Point and Auto-RP for information on configuring static RP and auto-RP.

Benefits of Tunneling to Connect Non-IP Multicast Areas

  • If the path between a source and a group member (destination) does not support IP multicast, a tunnel between them can transport IP multicast packets.

How to Configure Multicast Routing over GRE Tunnel

Configuring a GRE Tunnel to Connect Non-IP Multicast Areas

You can configure a GRE tunnel to transport IP multicast packets between a source and destination that are connected by a medium that does not support multicast routing.

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip multicast-routing

Example:


Device(config)# ip multicast-routing

Enables IP multicast routing.

Step 4

interface tunnel number

Example:


Device(config)# interface tunnel 0

Enters tunnel interface configuration mode.

Step 5

ip address ip_address subnet_mask

Example:


Device(config-if)# ip address 192.168.24.1 255.255.255.252

Configures IP address and IP subnet.

Step 6

ip pim sparse-mode

Example:


Device(config-if)# ip pim sparse-mode

Enables sparse mode of operation of Protocol Independent Multicast (PIM) on the tunnel interface with one of the following mode of operation:

Step 7

tunnel source { ip-address | interface-name }

Example:


Device(config-if)# tunnel source 100.1.1.1

Configures the tunnel source.

Step 8

tunnel destination { hostname | ip-address }

Example:


Device(config-if)# tunnel destination 100.1.5.3

Configures the tunnel destination.

Step 9

end

Example:


Device(config-if)# end

Ends the current configuration session and returns to privileged EXEC mode.

Step 10

show interface type number

Example:


Device# show interface tunnel 0

Displays tunnel interface information.

Tunneling to Connect Non-IP Multicast Areas Example

The following example shows multicast-routing between a Catalyst switch through a GRE tunnel.

Figure 1. Tunnel Connecting Non-IP Multicast Areas

In the figure above, the multicast source (10.1.1.1) is connected to Catalyst Switch-1 and is configured for multicast group 239.1.1.20. The multicast receiver (10.2.2.3) is connected to Catalyst Switch-2 and is configured to receive multicast packets for group 239.1.1.20. Separating Switch-1 and Switch-2 is an IP cloud, which is not configured for multicast routing.

A GRE tunnel is configured between Switch-1 to Switch-2 sourced with their loopback interfaces. Multicast-routing is enabled on Switch-1 and Switch-2. The ip pim sparse-mode command is configured on tunnel interfaces to support PIM in the sparse mode. Sparse mode configuration on the tunnel interfaces allows sparse-mode packets to be forwarded over the tunnel depending on rendezvous point (RP) configuration for the group.

Switch-1 Configuration: 


Device(config)# ip multicast-routing 
Device(config)# interface Loopback0   //Tunnel source interface 
Device(config-if)# ip address 2.2.2.2 255.255.255.255 

Device(config)# interface Tunnel 10     //Tunnel interface configured for PIM traffic
Device(config-if)# ip address 192.168.24.1 255.255.255.252
Device(config-if)# ip pim sparse-mode
Device(config-if)# ip nhrp map 192.168.24.3  4.4.4.4  //NHRP may optionally be configured to dynamically discover tunnel end points.
Device(config-if)# ip nhrp map multicast 4.4.4.4
Device(config-if)# ip nhrp network-id 1
Device(config-if)# ip nhrp nhs 192.168.24.3
Device(config-if)# tunnel source Loopback0
Device(config-if)# tunnel destination 4.4.4.4

Device(config)# interface GigabitEthernet 0/0/0       //Source interface
Device(config-if)# ip address 10.1.1.2 255.255.255.0 
Device(config-if)# ip pim sparse-mode

Switch-2 Configuration: 

Device(config)# ip multicast-routing
Device(config)# interface Loopback0   	//Tunnel source interface
Device(config-if)# ip address 4.4.4.4 255.255.255.255 

Device(config)# interface Tunnel 10 	    //Tunnel interface configured for PIM traffic
Device(config-if)# ip address 192.168.24.2 255.255.255.252
Device(config-if)# ip nhrp map 192.168.24.4 2.2.2.2 	//NHRP may optionally be configured to dynamically discover tunnel end points.
Device(config-if)# ip nhrp map multicast 2.2.2.2
Device(config-if)# ip nhrp network-id 1
Device(config-if)# ip nhrp nhs 192.168.24.4
Device(config-if)# ip pim sparse-mode
Device(config-if)# tunnel source Loopback0
Device(config-if)# tunnel destination 2.2.2.2

Device(config)# interface GigabitEthernet 0/0/0      //Receiver interface
Device(config-if)# ip address 10.2.2.2 255.255.255.0 
Device(config-if)# ip pim sparse-mode

Additional References for Multicast Routing over GRE Tunnel

Related Documents

Related Topic Document Title

For complete syntax and usage information for the commands used in this chapter.

See the IP Multicast Routing Commands section of the Command Reference (Catalyst 9400 Series Switches)

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

MIBs

MIB MIBs Link

All the supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/support

Feature Information for Multicast Routing over GRE Tunnel

The 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.
Table 1. Feature Information for Multicast Routing over GRE Tunnel

Feature Name

Releases

Feature Information

Multicast Routing over GRE Tunnel

Cisco IOS XE Everest 16.6.1

This chapter describes how to configure a GRE tunnel to tunnel IP multicast packets between non-IP multicast areas.

This feature was implemented on the following platforms:

  • Cisco Catalyst 9400 Series Switches