IPSec VPN Tunnels
Network Security

IPSec VPN Tunnels

Table of Contents

IPSec VPN Tunnels

Explains the steps involved in creating an IPSec VPN tunnel.
Where Can I Use This?
What Do I Need?
  • Prisma Access
  • PAN-OS
No license required
The process of creating an IPSec tunnel first starts to establish a preparatory tunnel that is encrypted and secured, and then from within that secure tunnel negotiate the encryption keys and parameters for the IPSec tunnel.
The VPN negotiations take place in two defined phases: phase one and phase two. The main purpose of phase one is to set up a secure encrypted channel through which the two peers can negotiate. When phase one finishes successfully, the peers quickly move on to phase two for negotiations.
If the tunnel interface is in a zone different from the zone where the traffic will originate or depart, then define a policy rule to allow the traffic to flow from the source zone to the zone containing the tunnel interface. Configuring the IP address on the tunnel interface is optional. You would need this IP address if you intend to run dynamic routing protocols over the tunnel interface.
While IPSec incorporates many component technologies and offers multiple encryption options, the basic operation includes the following five main procedures:
  • Interesting Traffic or On-Demand
    —The IPSec tunnel policy rule and the route table determines which type of traffic is considered to be “interesting” or is captured “on-demand” and, therefore, protected. How the PAN-OS VPN security policy gets implemented depends on the device platform. The access lists interpret IPSec policy rule to determine which traffic will be protected by IPSec.
    The IPSec tunnel comes up only when there is an interesting traffic destined to the tunnel. To manually initiate the tunnel, check the tunnel status and clear tunnels by referring to troubleshooting site-to-site VPN issues using the CLI.
  • IKE Phase 1
    —IKE is a key management protocol standard used with IPSec. IKE authenticates each peer in an IPSec session, automatically negotiates two levels of SAs, and handles the exchange of session keys accomplished in two phases: phase 1 and phase 2.
    The main purpose of IKE phase 1 is to authenticate the IPSec peers and to set up a secure channel between the peers.
  • IKE Phase 2
    —IKE negotiates the stricter IPSec Security Associations (SA) parameters between the peers.
  • IPSec Data Transfer
    —Qualifying data is transferred between IPSec peers. Information is exchanged through IPSec sessions based on the method for defining interesting traffic. Packets are encrypted and decrypted at the IPSec peers using any encryption specified in the IPSec SA.
  • IPSec Tunnel Session Termination
    —The IPSec session can be terminated because the traffic ended and the IPSec SA was deleted or the SA can timeout based on either SA lifetime setting. The SA timeout can be after a specified number of seconds or a specified number of bytes passed through the connection.
    The keys are discarded when SAs terminate, requiring IKE to perform a new phase two and, possibly, a new phase one negotiation. New SAs can be established before the current ones expire, maintaining uninterrupted data flows.
    The IPSec session terminates through deletion or by timing out.

IPSec Tunnel Policy Rule Implementation on Palo Alto Networks Next-Generation Firewalls

Encapsulating a packet for secure transportation on the network is accomplished by means of the IPsec protocol. For example, in the case of a site-to-site VPN, a source host in a network transmits an IP packet. When that packet reaches the edge of the network, it makes contact with a VPN gateway. The VPN gateway that corresponds with that network encrypts the private IP packet and relays it over an ESP tunnel to a peer VPN gateway at the edge of the next network, the gateway of which decrypts the packet and delivers it to the destination host.
The policy-based VPNs have specific security rules, policy rules, or access-lists (such as source addresses, destination addresses, and ports) that are configured for permitting the interesting traffic through IPSec tunnels. These rules are referenced during the quick mode (or IPSec phase 2), and are exchanged in the first or the second messages as the proxy IDs. If the Palo Alto Networks firewall is not configured with the proxy ID settings, then the firewall sets the proxy ID with the default values (source ip =, destination ip =, application:any) and exchanges it with the peer during the first or the second message of the quick mode.

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