Can Spanning-tree BPDU be transferred across ACI interstite overlay?

[vacumjh]

In a ACI MultiSite environment, say VLAN 10 is stretched crossed between two sites. Within each site, there is NXOS switch connected to the leaf switches with L2 trunk, including VLAN 10.

So will VLAN 10 spanning-tree BPDU be transferred across the ISN through overlay between site 1 and site 2? If so, anyway to prevent BPDU to be transferred across?

[M02@rt37]

Hello @vacumjh 

In an ACI MultiSite environment where VLAN 10 is stretched across two sites, spanning-tree BPDU information is not transferred across the inter-site network  by default. ACI MultiSite uses a concept called End Point Groups (EPGs) and contracts to handle communication between sites.

ACI MultiSite leverages MP-BGP for inter-site communication and doesn't extend Layer 2 constructs like spanning tree across sites. The communication between sites is generally at Layer 3, and traffic between EPGs is handled through the underlying infrastructure.

So, you don't need to worry about spanning-tree BPDU information being transferred across the ISN in ACI MultiSite. The design focuses on scalable and efficient communication between sites without extending Layer 2 domains across the WAN.

[Ruben Cocheno]

@vacumjh

Even though ACI does not generate STP BPDUs, ACI switches will forward STP BPDUs across EPGs on which they are received. In fact, we want ACI to forward the BPDUs across to other switches! This allows the externally connected switches to maintain a loop-free topology and avoid broadcast storms and other nastiness that goes hand-in-hand when layer-2 loops form!

Also keep in mind to use MCP Fabric-wide, and on all interfaces. MCP detects loops from external sources (i.e., misbehaving servers, external networking equipment running STP) and will err-disable the interface on which ACI receives its own packet.

if you dont want to forward STP across, you can use BPDU filter at the IPG level.