Sometimes you will have some L2 domains (Bridge Domains – BD) in your datacenter that will be used with hardware appliances like F5 NLB or something like an additional firewall, WAF or something similar. That is the case where ACI will not route or bridge but the only L3 point of exit from that kind of segment would be on actual hardware appliance outside ACI Fabric – connected to the Leaf port.
We will take an example here and use it throughout the article where BIG IP F5 NLB is used as an L3 termination of L2 BD 10.10.10.0/24.
F5 is directly connected to ACI Leaf and routing from 10.10.10.0/24 subnet (L2 BD) is done directly on F5 device which is default gateway for that subnet endpoints.
In those cases for some particular implementations when you decide not to use PBR or Service graphs, it will happen that appliances like our F5 would become L3 termination for some ACI L2 BD like the 10.10.10.0/24 from my beautiful image above.