VLAN Encapsulation in ACI
There are two types of VLANs used in ACI
- External VLAN: Used for External Communication and Integration
- Internal VLAN: It is also called as Platform Independent Vlan whose scope is local to each leaf. ACI has no control how Platform VLAN is allocated to traffic going via leaf. APIC allocates PI VLAN per EPG, Per BD and these allocation is local to leaf and is different to each Leaf.
Cisco ACI fabric internally does not use VLANs as traditional switches but it translates externally connected VLANs to Flooding Domain, Bridge Domain and VXLANs. All of this is happening at the ingress to the fabric.
Here we can see the ACI has allocated the Platform VLAN to each VLAN which its receives from ingress port. Example from port Eth1/11, Traffic comes to Leaf with encapsulation of Ethernet vlan 1675 and upon receive, it allocates VLAN 12 randomly on that leaf switch.
show vlan extended output command you can see how internal VLANs are encapsulated to VXLANs or external VLANs. With this command, you can easily see which external VLANs are used on the particular leaf switch.