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Multicast PIM-ASM and PIM-SSM Configuration Guide

1. Introduction

This guide provides a comprehensive, step-by-step tutorial for establishing IPv4 Multicast networks on the Asterfusion Open Intelligent Gateway. By leveraging the high-performance VPP data plane, you will learn how to build multicast routing architectures that are both highly efficient and scalable for enterprise and data center environments.

2. What This Guide Will Accomplish

By following this guide, you will learn how to deploy robust multicast architectures. The configuration scenarios are structured into two distinct phases:

2.1 Phase 1: Establish PIM-ASM Underlay

  • Scenario 1: Basic PIM-SM with Static RP: Establishing a foundational PIM-ASM network using OSPF as the underlay routing protocol with a central Rendezvous Point.
  • Scenario 2: Multicast over BGP: Deploying PIM-ASM over a BGP underlay to validate advanced RPF checks within a typical Spine-Leaf topology.

2.2 Phase 2: Advanced Capabilities

  • Scenario 3: PIM-SSM Built directly upon the underlay established in Phase 1, this scenario demonstrates how to migrate to a highly efficient, RP-less architecture using IGMPv3 and explicit (S, G) tree building.

3. Scenario 1: Basic PIM-SM with Static RP

3.1 Scenario Overview

In this scenario, we establish a standard PIM-SM domain without using Loopback interfaces. The Spine’s Ethernet1 IP (10.0.1.2) serves as the Static RP for the entire domain.

Device Roles:

  • Source DR (Leaf1): Gateway for the Multicast Source.
  • RP (Spine): The central Rendezvous Point. Its downlink interface IP (10.0.1.2) is used as the RP address.
  • Receiver DR (Leaf2): Gateway for the Receiver, running IGMPv3.

3.2 Network Topology Plan

Network Topology for Multicast PIM-ASM and PIM-SSM
Role
Device
Interface
IP Address
 Function
Source DR
Leaf1
Ethernet 1 (Downlink)
192.168.10.1/24
 Connects to Source PC
Ethernet 2 (Uplink)
10.0.1.1/30
Connects to Spine (Ethernet1)
RP / Spine
Spine
Ethernet 1 (Downlink)
10.0.1.2/30
Connects to Leaf1 (RP Address)
Ethernet 3 (Downlink)
10.0.2.1/30
Connects to Leaf2
Receiver DR
Leaf2
Ethernet 1 (Uplink)
10.0.2.2/30
Connects to Spine (Ethernet3)
Ethernet 2 (Downlink)
192.168.20.1/24
Connects to Receiver PC

3.3 Configuration Steps

Configure Source DR (Leaf1)

Leaf1 connects to the Source PC via Ethernet 1 and the Spine via Ethernet 2. The critical step is enabling the unknown-multicast trap to ensure the first multicast packet is sent to the CPU for PIM registration.

sonic# configure terminal

# 1.Configure Interfaces
sonic(config)# interface ethernet 1
sonic(config-if-1)# description Link_to_Source_PC
sonic(config-if-1)# ip address 192.168.10.1/24
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 2
sonic(config-if-2)# description Link_to_Spine
sonic(config-if-2)# ip address 10.0.1.1/30
sonic(config-if-2)# ip pim
sonic(config-if-2)# exit

# 2.Enable Control Plane Trap
sonic(config)# unknown-multicast trap

# 3.Configure Static RP
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 4.Configure Underlay Routing (OSPF)
sonic(config)# router ospf
sonic(config-router)# network 10.0.1.0/30 area 0
sonic(config-router)# network 192.168.10.0/24 area 0
sonic(config-router)# exit

Configure Spine (RP)

The Spine acts as the Rendezvous Point. We use the IP address of Ethernet 1 (10.0.1.2) as the RP address for the entire network.

# 1.Configure Interfaces
sonic(config)# interface ethernet 1
sonic(config-if-1)# description Link_to_Leaf1
sonic(config-if-1)# ip address 10.0.1.2/30
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 3
sonic(config-if-3)# description Link_to_Leaf2
sonic(config-if-3)# ip address 10.0.2.1/30
sonic(config-if-3)# ip pim
sonic(config-if-3)# exit

# 2.Configure Static RP
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 3.Configure Underlay Routing (OSPF)
sonic(config)# router ospf
sonic(config-router)# network 10.0.1.0/30 area 0
sonic(config-router)# network 10.0.2.0/30 area 0
sonic(config-router)# exit

Configure Receiver DR (Leaf2)

Leaf2 connects to the Spine via Ethernet 1 and the Receiver PC via Ethernet 2. IGMPv3 is explicitly enabled on the receiver-facing interface.

# 1.Configure Interfaces
sonic(config)# interface ethernet 1
sonic(config-if-1)# description Link_to_Spine
sonic(config-if-1)# ip address 10.0.2.2/30
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 2
sonic(config-if-2)# description Link_to_Receiver_PC
sonic(config-if-2)# ip address 192.168.20.1/24
sonic(config-if-2)# ip igmp
sonic(config-if-2)# ip pim
sonic(config-if)# exit

# 2.Configure Static RP
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 3.Configure Underlay Routing (OSPF)
sonic(config)# router ospf
sonic(config-router)# network 10.0.2.0/30 area 0
sonic(config-router)# network 192.168.20.0/24 area 0
sonic(config-router)# exit

3.4 Verification

Control Plane Verification

  • Verify PIM Neighbors (on Spine)

sonic# show ip pim neighbor

Output 1 in PIM-ASM Configuration Guide
  • Verify RP Mapping (Any Device)

sonic# show ip pim rp-info

Output 2 in PIM-ASM Configuration Guide
Output 3 in PIM-ASM Configuration Guide

Data Plane Verification

Send multicast traffic from Source (192.168.10.10) to Group (239.1.1.1) and have the Receiver join the group.

  • Leaf1 (Source DR) – Verify Registration

sonic# show ip mroute

Output 4 in PIM-ASM Configuration Guide
  • Spine (RP) – Verify Forwarding Tree

sonic# show ip mroute

Output 5 in PIM-ASM Configuration Guide
  • Leaf2 (Receiver DR) – Verify Reception

sonic# show ip mroute

Output 6 in PIM-ASM Configuration Guide

4. Scenario 2: Multicast over BGP (Data Center Architecture)

4.1 Scenario Overview

This scenario replicates a typical Data Center Spine-Leaf architecture using BGP as the underlay routing protocol. Unlike OSPF, BGP does not automatically flood routing information. This scenario validates that the AsterNOS PIM stack can correctly perform RPF (Reverse Path Forwarding) checks based on BGP routing tables.

Key Changes:

  • Underlay Protocol: Replaced OSPF with BGP.
  • Routing Logic: Leaf2 must learn the RP address via BGP to send PIM Join messages.

4.2 Configuration Steps

Configure Source DR (Leaf1)

Leaf1 connects to the Source (192.168.10.10). It must advertise the source subnet into BGP so the Spine knows where the multicast source is located.

# 1.Interface Configuration
sonic(config)# interface ethernet 1
sonic(config-if-1)# ip address 192.168.10.1/24
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 2
sonic(config-if-2)# ip address 10.0.1.1/30
sonic(config-if-2)# ip pim
sonic(config-if-2)# exit

# 2. Enable Control Plane Trap
sonic#(config)# unknown-multicast trap

# 3.Static RP Configuration
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 4.BGP Configuration (AS 65001)
sonic(config)# router bgp 65001
sonic(config-router)# bgp router-id 1.1.1.1
sonic(config-router)# no bgp ebgp-requires-policy
sonic(config-router)# bgp default ipv4-unicast

sonic(config-router)# neighbor 10.0.1.2 remote-as 65000

sonic(config-router)# address-family ipv4 unicast
sonic(config-router-af)# neighbor 10.0.1.2 activate
sonic(config-router-af)# network 192.168.10.0/24
sonic(config-router-af)# exit
sonic(config-router)# exit

Configure Spine (RP)

# 1.Interface Configuration
sonic(config)# interface ethernet 1
sonic(config-if-1)# ip address 10.0.1.2/30
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 3
sonic(config-if-3)# ip address 10.0.2.1/30
sonic(config-if-3)# ip pim
sonic(config-if-3)# exit

# 2.Static RP Configuration
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 3.BGP Configuration (AS 65000)
sonic(config)# router bgp 65000
sonic(config-router)# bgp router-id 2.2.2.2
sonic(config-router)# no bgp ebgp-requires-policy
sonic(config-router)# bgp default ipv4-unicast

sonic(config-router)# neighbor 10.0.1.1 remote-as 65001
sonic(config-router)# neighbor 10.0.2.2 remote-as 65002

sonic(config-router)# address-family ipv4 unicast
sonic(config-router-af)# neighbor 10.0.1.1 activate
sonic(config-router-af)# neighbor 10.0.2.2 activate
sonic(config-router-af)# network 10.0.1.0/30
sonic(config-router-af)# exit
sonic(config-router)# exit

Configure Receiver DR (Leaf2)

Leaf2 (AS 65002) connects to the Receiver. It learns the RP route via BGP.

# 1.Interface Configuration
sonic(config)# interface ethernet 1
sonic(config-if-1)# ip address 10.0.2.2/30
sonic(config-if-1)# ip pim
sonic(config-if-1)# exit

sonic(config)# interface ethernet 2
sonic(config-if-2)# ip address 192.168.20.1/24
sonic(config-if-2)# ip pim
sonic(config-if-2)# ip igmp
sonic(config-if-2)# exit

# 2.Static RP Configuration
sonic(config)# ip pim rp 10.0.1.2 224.0.0.0/4

# 3.BGP Configuration (AS 65002)
sonic(config)# router bgp 65002
sonic(config-router)# bgp router-id 3.3.3.3
sonic(config-router)# no bgp ebgp-requires-policy
sonic(config-router)# bgp default ipv4-unicast

sonic(config-router)# neighbor 10.0.2.1 remote-as 65000

sonic(config-router)# address-family ipv4 unicast
sonic(config-router-af)# neighbor 10.0.2.1 activate
sonic(config-router-af)# network 192.168.20.0/24
sonic(config-router-af)# exit
sonic(config-router)# exit

4.3 Verification

  • Verify Underlay Routing (BGP)

sonic# show ip route

  • Leaf1:
IP-multicast-Use-Case Figure 2-1
  • RP:
IP-multicast-Use-Case Figure 2-2
  • Leaf2:
IP-multicast-Use-Case Figure 2-3

  • Verify Multicast Routing (PIM over BGP)

Check the multicast routing table after the receiver joins the group.

sonic# show ip mroute

  • Leaf1:
IP-multicast-Use-Case Figure 2-4
  • RP:
IP-multicast-Use-Case Figure 2-5
  • Leaf2:
IP-multicast-Use-Case Figure 2-6

5. Scenario 3: PIM-SSM (Source Specific Multicast)

5.1 Scenario Overview

This scenario demonstrates the transition from ASM to PIM-SSM. In this mode, the RP is eliminated, and the multicast distribution tree is built directly from the receiver to the source using IGMPv3.

5.2 Configuration Steps

This configuration assumes the physical underlay (Scenario 1 or 2) is already functional.

Upgrade to IGMPv3(Leaf2 Only)

To process Source-Specific joins, the receiver-facing interface on Leaf2 must be upgraded to IGMP version 3.

sonic(config)# interface ethernet 2
sonic(config-if)# ip igmp version 3
sonic(config-if)# exit

Global RP Cleanup (All Devices)

The core of SSM is the complete absence of a Rendezvous Point. You must remove the static RP configuration from Leaf1, Spine, and Leaf2 to tear down the ASM shared tree mechanism.

sonic(config)# no ip pim rp 10.0.1.2 224.0.0.0/4

Note:  (No further router configuration is needed. The network is now ready for SSM.)

Flow Triggering Requirements

To establish the SSM Shortest Path Tree (SPT), the following conditions must be met by the end-stations:

  • Source Side: Outbound multicast traffic must target a destination IP within 0.0.0/8.
  • Receiver Side: The host must issue an IGMPv3 Membership Report that includes the specific Source IP (192.168.10.10) and Group IP.

5.3 Verification

  • Verify IGMPv3 Join

Check the IGMP groups on Leaf2 to ensure the receiver has successfully sent an IGMPv3 Source-Specific Join.

sonic# show ip igmp groups

show ip igmp groups output in PIM-SSM Configuration Guide

  • Verify PIM-SSM Routing Table

Check the multicast routing table on Leaf2 to confirm the Shortest Path Tree (SPT) has been established directly to the source.

sonic# show ip mroute

show ip mroute output in PIM-SSM Configuration Guide

6. Conclusion

This guide has verified the comprehensive multicast routing capabilities of AsterNOS, enabling highly efficient traffic distribution across diverse topologies. The completed scenarios demonstrate that AsterNOS provides the essential flexibility required for modern networks, seamlessly supporting both traditional PIM-ASM and advanced, RP-less PIM-SSM architectures.