L2 DataPath – Deep Dive

L2 DataPath – Deep Dive

L2 DataPath Examples

In this we will learn how L2 traffic flows between ACI fabrics via different example. Before we go to the example, let’s understand the traffic flow via Flow chart.

If destination MAC is known to an ingress leaf the packet is forwarded either to local port (if the endpoint is on local leaf) or to remote leaf (if the endpoint is not on local leaf).

If destination MAC is not known to and ingress leaf then there are two options:

  • If BD is in Hardware-proxy mode the packet is forwarded to Spine Proxy and spine either drops the packet (destination MAC address is not known to Spine) or forwards the packet to remote leaf (destination MAC address is known to Spine)
  • If BD is in Flood mode the packet is flooded within BD

Here we will discuss two case scenario each with one or two example

Scenario 1:  Both EP belong to same EPG with same IP subnet on different Leaf and both host knows MAC of each other. EPG belong to L2 BD.

Example 1: Both Leaf knows Source and Destination MAC in its LST and GST table.


Let‘s look at an example where the traffic flows between two endpoints in the same EPG in the same L2 BD; MAC addresses of both endpoints are known.

  • VM A is known as local to leaf switches 1 and 2 (vPC) and VM B is known as remote to these two switches.
  • VM A is known as remote to Leaf 4 and VM B is known as local to Leaf 4.


  • RS

    Super Duper Like ... one of the most difficult topic explained in simple way

  • Wk

    If possible more of the CLI show command along the way of explanation, this will be better for understanding... thank you in advance

  • JO

    ACI Forwarding is explained in very deep dive manner, It helped me to understand how traffic flows in ACI , Very good content and well explained


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