Looking to confirm the understanding of these scenarios about per-packet and per-flow within the context of ACI, is this correct? If not, how does it actually work?
1. Intra fabric forwarding (within a single ACI fabric1) - ACI will utilize PER-PACKET ECMP load balancing if forwarding between two endpoints within the SAME fabric itself. This is because an endpoint1 on Leaf1 will forward per packet to spine1/2, then spine1/2 forwards to the destination leaf8 which receives the per packet flows and then sends them to endpoint2.
2. Inter fabric forwarding (ACI fabric1 to ISN to ACI fabric2) - ACI will utilize PER-FLOW ECMP load balancing if fowarding between two endpoints in DIFFERENT fabrics. This is because the ISN network(s) are not part of ACI and we cannot reliably send packets from both spines into the ISN devices(per packet). So if ACI understands the destination EP is in another fabric or external network (ie out an external connection) then it should only send traffic from EP1 on Leaf1 to Spine1 OR Spine2 (but not both spines). Then the chosen spine continues to fwd the flow into the ISN via a single connection, aka PER-FLOW.
thanks,
Dan
CCIE RS 34827
