ArubaOS-CX IGMP Snooping and PIM Sparse Mode Configuration

Multicast on ArubaOS-CX (AOS-CX) is built from three pieces: IGMP snooping to constrain traffic inside each VLAN, a PIM variant to build the distribution tree between subnets, and a Rendezvous Point when PIM Sparse Mode is used. Most deployments that fail in production fail on the third piece or forget IGMP snooping entirely, so the access layer floods video and imaging traffic to every port. This article gives the configuration order, the VSX-specific commands, and the verification that shows where the tree actually broke.

Step 1: Enable Multicast Routing and PIM

switch(config)# router pim
switch(config-pim)# enable
switch(config-pim)# rp-address 10.255.0.1
switch(config-pim)# exit

PIM Sparse Mode is the default choice for campus and data center networks: traffic only follows a path where a receiver has joined. Dense Mode is reserved for lab or very small topologies because it floods first and prunes afterwards.

Step 2: SVI-Level IGMP and PIM

switch(config)# interface vlan 20
switch(config-if-vlan)# ip address 10.20.0.1/24
switch(config-if-vlan)# ip igmp enable
switch(config-if-vlan)# ip igmp version 2
switch(config-if-vlan)# ip pim-sparse enable
switch(config-if-vlan)# ip pim-sparse hello-interval 30
switch(config-if-vlan)# exit

Enable PIM on every routed interface that may carry the stream (including uplinks to the core), and IGMP only where receivers exist. On the interface facing the multicast source, no IGMP is required but PIM is.

Step 3: IGMP Snooping and the Querier

switch(config)# vlan 20
switch(config-vlan)# ip igmp snooping enable
switch(config-vlan)# ip igmp snooping querier
switch(config-vlan)# ip igmp snooping version 2
switch(config-vlan)# exit

Without a querier, group membership times out and streams stop after a few minutes; without snooping, all multicast traffic within the VLAN is flooded. In a VSX pair, configure the querier on only one side or split the scope by VLAN to avoid duplicate queries.

Step 4: VSX Virtual Neighbors (VXLAN Fabrics)

switch(config)# interface vlan 30
switch(config-if-vlan)# ip pim-sparse enable
switch(config-if-vlan)# ip pim-sparse vsx-virtual-neighbor
switch(config-if-vlan)# exit

On VSX VTEPs, vsx-virtual-neighbor lets both peers process IGMP and PIM joins regardless of the DR state, which prevents the multicast data path from breaking when the designated router is on the standby peer. Register source and RP candidates are configured on the fabric-wide PIM router when anycast gateway is used.

Step 5: Designated Router and RP Options

switch(config)# interface vlan 20
switch(config-if-vlan)# ip pim-sparse dr-priority 100
switch(config-if-vlan)# exit
switch(config)# router pim
switch(config-pim)# rp-candidate source-ip-interface loopback 0 group-prefix 224.0.0.0/4
switch(config-pim)# bsr-candidate source-ip-interface loopback 0
switch(config-pim)# exit

Either pin an RP with a static rp-address or let BSR/auto-RP discover it; mixing static and dynamic on the same group range is the classic cause of one-way flows.

Verification and Common Faults

show ip multicast routing
show ip pim interface
show ip pim neighbor
show ip igmp snooping vlan 20
show ip mroute 239.1.1.1

• Streams work in one VLAN but not another: IGMP snooping missing on the second VLAN.
• Sources register but receivers get nothing: no RP reachable or the RP range does not cover the group.
• Traffic floods to all ports: snooping disabled, or the mrouter port was not learned - enable PIM on the uplink.
• After a VSX role change the stream stalls: vsx-virtual-neighbor missing on the SVI.

Related reading: the VSX pair bring-up in ArubaOS-CX VSX configuration, port roles in ArubaOS-CX access vs trunk configuration, and why multicast needs priority treatment in ArubaOS-CX QoS trust and queue profiles.

原文链接：HPE Aruba Networking AOS-CX multicast configuration task list