Subinterfaces in Palo Alto Networks firewalls allow for logical segmentation of a physical interface, enabling the handling of multiple VLANs or traffic types over a single physical connection. They are applicable in Layer 3, Layer 2, and Virtual Wire interface types, each serving distinct purposes.
Layer 3 Subinterfaces
Layer 3 subinterfaces are used to route traffic between different VLANs. Each subinterface is assigned an IP address and a VLAN tag, allowing the firewall to act as a gateway for multiple VLANs over a single physical interface.
Use Case:
Implemented in "router-on-a-stick" configurations to manage inter-VLAN routing.
Configuration:
Assign a unique VLAN tag and IP address to each subinterface, and associate it with a virtual router and security zone.
Benefits:
Efficient use of physical interfaces, simplified network design, and centralized routing control.
Layer 2 Subinterfaces
Layer 2 subinterfaces enable the firewall to handle multiple VLANs by associating each subinterface with a specific VLAN ID. Traffic is switched based on MAC addresses, and VLANs are used to segment broadcast domains.
Use Case:
Used in environments where the firewall provides Layer 2 switching between VLANs.
Configuration:
Create subinterfaces with specific VLAN tags and assign them to appropriate security zones.
Benefits:
Allows for granular control and monitoring of VLAN-segmented traffic without Layer 3 routing.
Virtual Wire Subinterfaces
Virtual Wire (vWire) subinterfaces allow the firewall to inspect and enforce policies on traffic based on VLAN tags or IP classifiers, even though the firewall is deployed transparently without IP addressing.
Use Case:
Ideal for environments requiring transparent inspection of VLAN-tagged traffic without altering the existing network topology.
Configuration:
Define subinterfaces with specific VLAN tags and associate them with security zones; optionally use IP classifiers for more granular traffic identification.
Benefits:
Enables policy enforcement and traffic segmentation in transparent deployments, facilitating multi-tenant environments and detailed traffic control.