Multicast

IP Multicast Multipath enables load balancing of multicast traffic across multiple equal-cost paths in a network. By default, multicast routing uses only one path from source to destination even when multiple equal-cost paths exist. The multipath feature allows routers to distribute multicast traffic across multiple paths, improving bandwidth utilization and providing better load distribution. The s-g-hash algorithm determines how multicast streams are mapped to available paths: the basic algorithm uses the source address only, while the next-hop-based algorithm considers both source and group addresses along with available next-hop interfaces, providing more granular load distribution across the network topology.

Diagram

Classes

configuration (iosxe.devices)

Name	Type	Constraint	Mandatory	Default Value
multicast	Class	[multicast]	No

multicast (iosxe.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
multipath	Boolean	true, false	No
multipath_s_g_hash	Choice	basic, next-hop-based	No
vrfs	List	[vrfs]	No

vrfs (iosxe.devices.configuration.multicast)

Name	Type	Constraint	Mandatory	Default Value
vrf	String		Yes
multipath	Boolean	true, false	No
multipath_s_g_hash	Choice	basic, next-hop-based	No

By enabling multicast multipath, you can improve network efficiency and utilize available bandwidth more effectively when multiple equal-cost paths exist between multicast sources and receivers.

Multicast Parameters

Key Components:

• Multipath (): Enables IP multicast multipath load balancing. When enabled, allows multicast traffic to be distributed across multiple equal-cost paths.

• S-G-Hash Algorithm (): Configures the source-group hash algorithm for multicast load balancing:

  • : Uses source address only for path selection
  • : Uses source, group, and next-hop information for more granular distribution

• VRF-Specific Configuration (): Enables multicast multipath and configures parameters within specific VRF instances.

Key Parameters Briefly Explained:

• : Enable/disable multicast multipath load balancing
• : Algorithm for distributing multicast streams ( or )
• : VRF-specific multicast multipath settings

You can use these multicast parameters to enable load balancing of multicast traffic across multiple equal-cost paths in your network. The basic algorithm provides simple source-based distribution, while next-hop-based provides more sophisticated load balancing by considering additional factors. Adjusting these parameters lets you optimize multicast traffic distribution based on your network topology and traffic patterns.

Sample Configuration

The following configuration describes how to set up IP multicast multipath on a Cisco IOS-XE device, including global configuration and VRF-specific settings.

ip multicast multipath s-g-hash next-hop-based
!
ip multicast vrf PROD_VRF multipath s-g-hash basic
ip multicast vrf GUEST_VRF multipath s-g-hash next-hop-based

Example YAML Code

The following YAML code defines multicast multipath configuration on an IOS-XE device, including global and VRF-specific settings.

iosxe:
  devices:
    - name: Device1
      configuration:
        multicast:
          multipath: true
          multipath_s_g_hash: next-hop-based
          vrfs:
            - vrf: PROD_VRF
              multipath: true
              multipath_s_g_hash: basic
            - vrf: GUEST_VRF
              multipath: true
              multipath_s_g_hash: next-hop-based

Real-World Use Cases

Use Case 1: Data Center with Redundant Paths

In a data center environment with multiple equal-cost paths between ToR (Top of Rack) and spine switches:

iosxe:
  devices:
    - name: DataCenterCore
      configuration:
        multicast:
          multipath: true
          multipath_s_g_hash: next-hop-based  # Better distribution for multiple streams

Use Case 2: Multi-VRF Environment

In a service provider network with separate VRFs for different customers:

iosxe:
  devices:
    - name: ServiceProviderEdge
      configuration:
        multicast:
          multipath: true
          multipath_s_g_hash: next-hop-based
          vrfs:
            - vrf: CUSTOMER_A
              multipath: true
              multipath_s_g_hash: basic  # Simpler algorithm for smaller deployment
            - vrf: CUSTOMER_B
              multipath: true
              multipath_s_g_hash: next-hop-based  # More streams, better distribution

Use Case 3: Campus Network with Video Streaming

For a campus network distributing video multicast streams across redundant core switches:

iosxe:
  devices:
    - name: CampusCore
      configuration:
        multicast:
          multipath: true
          multipath_s_g_hash: next-hop-based  # Optimal for multiple video streams