Hi,
You can enable or disable BUM (Broadcast, Unknown unicast, and Multicast) forwarding per bridge domain in ACI Multipod.
And you can check "Delivery of BUM Traffic between Pods"
1. EP1 belonging to BD1 originates a BUM frame.
2. The frame is encapsulated by the local leaf node and destined to the multicast group GIPo1 associated to BD1. As a consequence, it is sent along one of the multi-destination tree assigned to BD1 and reaches all the local spine and leaf nodes where BD1 has been instantiated.
3. Spine 1 is responsible for forwarding BUM traffic for BD1 toward the IPN devices, leveraging the specific link connected to IPN1.
4. The IPN device receives the traffic and performs multicast replication toward all the Pods from which it received an IGMP Join for GIPo1. This ensures that BUM traffic is sent only to Pods where BD1 is active (i.e. there is at least an endpoint actively connected in the Bridge Domain).
5. The spine that sent the IGMP Join toward the IPN devices receives the multicast traffic and forwards it inside the local Pod along one of the multi-destination trees associated to BD1. All the leafs where BD1 has been instantiated receive the frame.
6. The leaf where EP2 is connected also receives the stream, decapsulates the packet and forwards it to EP2.
https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737855.html
Meanwhile, if you would know more about BUM forwarding overview and ACI Multipod scenario troubleshooting, you can refer to Troubleshoot ACI Intra-Fabric Forwarding - MultiPod Forwarding
https://www.cisco.com/c/en/us/support/docs/cloud-systems-management/application-policy-infrastructure-controller-apic/218013-troubleshoot-aci-intra-fabric-forwarding.html
Multi-Pod broadcast, unknown unicast, and multicast (BUM) forwarding overview
In ACI, traffic is flooded via overlay multicast groups in many different scenarios. For example, flooding occurs for:
- Multicast and broadcast traffic.
- Unknown unicast that must be flooded.
- Fabric ARP glean messages.
- EP announce messages.
Many features and functionality rely on BUM forwarding.
Within ACI, all Bridge Domains are allocated a multicast address known as a Group IP Outer (or GIPo) address. All traffic that must be flooded within a Bridge Domain is flooded on this GIPo.
Note that disabling BUM forwarding for a Bridge Domain may impact the functionality of certain applications or services that rely on multicast or broadcast traffic. Therefore, it is recommended to carefully evaluate the impact of this configuration change before implementing it in a production environment.
