To enable the Advanced Routing Engine (ARE) on a Palo Alto Networks firewall, the license for the ARE must be applied first. Without the proper license, the firewall cannot activate and use the advanced routing features provided by ARE, such as support for more complex routing protocols (e.g., BGP, OSPF, etc.).

Once the license is applied and validated, the routing engine can be configured, allowing the creation of logical routers and routing policies.

The Proxy IDs (or Traffic Selectors) define the local and remote subnets that are allowed to communicate over the IPSec tunnel. If the Proxy IDs on the Palo Alto Networks firewall do not match the configuration on the Cisco ASA, the tunnel will fail to establish because the firewalls won't agree on which traffic to encrypt. Ensuring that the Proxy IDs match between the Palo Alto Networks firewall and the Cisco ASA will resolve the issue.

Use of dynamic routing protocols: An IP address is needed on the tunnel interface to participate in dynamic routing protocols (like OSPF, BGP, etc.) over the tunnel. This allows the firewall to advertise routes and receive updates over the tunnel.

Tunnel monitoring: The IP address on the tunnel interface can also be used for monitoring the tunnel's status. Tunnel monitoring (such as IPSec tunnel monitoring) requires an IP address on the tunnel interface to check the health and availability of the tunnel.

When a Palo Alto Networks firewall receives routes for the same destination from different routing protocols, it uses the administrative distance (AD) to determine the best route. The administrative distance is a measure of the trustworthiness of a route, with a lower value indicating higher preference. The firewall will choose the route with the lowest administrative distance to populate its forwarding table.

In the context of GlobalProtect with certificate-based authentication, certificate profiles are used to ensure proper validation of the certificates. They perform the following functions:

Define trust anchors, which are the root and intermediate Certificate Authorities (CAs) that the firewall trusts to authenticate certificates.

Specify revocation checks, such as CRL (Certificate Revocation List) and OCSP (Online Certificate Status Protocol), to ensure that the certificates being used have not been revoked.

Map certificate attributes, such as the Common Name (CN), which helps in authenticating users and devices based on their certificates.

By default, the Autonomous Digital Experience Manager (ADEM) traffic is configured to use the management interface in a Palo Alto Networks firewall. The management interface is typically used for management-related traffic, such as monitoring and logging, and it is configured to handle ADEM-related traffic for the optimal performance of digital experience monitoring features.

This default configuration helps ensure that ADEM traffic does not interfere with regular traffic that may traverse other interfaces, such as traffic from security zones or IPSec tunnels.

Establishing a functional IPSec VPN on a Palo Alto Networks Next-Generation Firewall requires addressing two distinct traffic flows: the management of the tunnel itself ( Control Plane ) and the transit of protected data ( Data Plane ).

First, to address the failure of the tunnel to establish, the firewall must have a security policy that permits the negotiation protocols. Specifically, a rule is required to allow ike (UDP/500), ipsec-esp-udp (UDP/4500 if NAT-T is used), and ipsec-esp (IP Protocol 50) between the source zone (where the firewall's public-facing interface resides) and the destination zone (where the partner’s gateway resides). Since the firewall is the endpoint for this negotiation, the destination zone is often the "local" zone or the specific external zone where the peer's IP is located.

Second, once the tunnel is established, the firewall must be configured to allow the actual application traffic. In the Palo Alto Networks zone-based architecture, traffic entering or exiting an IPSec tunnel is associated with a Tunnel Interface . This interface must be assigned to a security zone. Because the default behavior for interzone traffic is to "Deny," the engineer must explicitly create a pair of security rules: one to allow traffic from the internal network zone to the tunnel interface's zone, and another to allow returning traffic from the tunnel interface's zone back to the internal zone. Without these rules, the tunnel may appear "active" in the logs, but all encapsulated production data will be dropped.