Comparison of Active/Passive and Active/Active HA Configurations

Overview

High Availability (HA) configurations in Palo Alto Networks firewalls are designed to ensure continuous network security and uptime. The two primary HA configurations are Active/Passive and Active/Active, each with its own operational mechanisms, advantages, and considerations.

Active/Passive HA Configuration

Operational Mechanism:

• Active Firewall: Handles all traffic processing under normal conditions.
• Passive Firewall: Remains synchronized with the Active firewall but does not process traffic unless a failover occurs.
• Failover Process: If the Active firewall experiences a failure, the Passive firewall transitions to Active status, ensuring uninterrupted traffic flow.

Advantages:

• Simplicity: Easier to configure and manage due to its straightforward design.
• Resource Optimization: The Passive firewall remains idle, consuming minimal resources until a failover is necessary.

Considerations:

• Resource Utilization: The Passive firewall's resources are underutilized during normal operations.
• Failover Time: There may be a brief interruption during the failover process, though this is typically minimal.

Active/Active HA Configuration

Operational Mechanism:

• Both Firewalls Active: Both firewalls actively process traffic, distributing the load between them.
• Session Handling: Sessions are distributed based on configured load-sharing algorithms, and session information is synchronized between firewalls.
• Failover Process: If one firewall fails, the other continues to handle all traffic, with session information intact due to synchronization.

Advantages:

• Load Balancing: Traffic load is shared between both firewalls, optimizing resource utilization and potentially improving performance.
• High Availability: Both firewalls are active, reducing the risk of downtime since either can take over if the other fails.

Considerations:

• Complexity: More complex to configure and manage due to the need for session synchronization and load-sharing configurations.
• Asymmetric Routing: Careful network design is required to handle asymmetric traffic flows, where traffic may enter through one firewall and return through another. This requires session synchronization to maintain session integrity.
• Potential Overhead: Synchronizing session information between firewalls introduces additional overhead, which may impact performance if not properly managed.

Active/Active HA with Floating IP Addresses

In an Active/Active High Availability (HA) configuration with floating IP addresses on Palo Alto Networks firewalls, both devices actively process traffic, and the floating IP addresses can move between the firewalls in the event of a failure. This setup ensures continuous availability and load balancing.

Key Components:

• Floating IP Addresses: Shared IP addresses that can move between HA firewalls upon failure, ensuring uninterrupted service.
• Virtual MAC Addresses: MAC addresses associated with floating IPs, allowing switches to redirect traffic to the active firewall hosting the floating IP.

Operational Overview:

1. Traffic Distribution: Clients are configured to use floating IP addresses as their default gateways. Both HA firewalls actively handle traffic, distributing the load based on configured algorithms.
2. Failover Process: If a firewall or link fails, the floating IP address and its associated virtual MAC address move to the operational firewall. The active firewall sends a gratuitous ARP to update network devices, ensuring traffic is directed to the correct firewall.
3. Session Persistence: Session information is synchronized between the HA firewalls. In case of failover, the operational firewall can continue sessions without interruption.

Considerations:

• Asymmetric Routing: Careful network design is required to handle asymmetric traffic flows, where traffic may enter through one firewall and return through another. This requires session synchronization to maintain session integrity.
• Complexity: Active/Active configurations with floating IPs introduce additional complexity compared to Active/Passive setups. Proper planning and understanding are essential to implement this configuration effectively.

Additional Resources:

For detailed configuration steps and best practices, refer to the official Palo Alto Networks documentation:

• Configure Active/Active HA with Floating IP Addresses
• Configure Active/Active HA with Floating IP Address Bound to Active-Primary Firewall

Active/Active HA with ARP Load-Sharing

In an Active/Active High Availability (HA) configuration with ARP Load-Sharing on Palo Alto Networks firewalls, both devices actively process traffic, distributing the load based on ARP responses.

Key Components:

• ARP Load-Sharing: Allows both firewalls to respond to ARP requests for a shared IP address, distributing client traffic between them. The device selection algorithm determines which firewall responds to the ARP request.
• Virtual MAC Addresses: Each firewall generates a unique virtual MAC address for the shared IP address, enabling correct traffic forwarding.

Operational Overview:

1. Traffic Distribution: Clients are configured with the shared IP address as their default gateway. Both firewalls respond to ARP requests, distributing traffic based on the selected device selection algorithm.
2. Failover Process: If a firewall fails, the shared IP address and its associated virtual MAC address move to the operational firewall. The active firewall sends gratuitous ARPs to update network devices, ensuring traffic is directed appropriately.

Considerations:

• Layer 3 Deployment: ARP Load-Sharing is suitable when end hosts use the firewall as their default gateway, and no Layer 3 device exists between the firewall and end hosts.
• Device Selection Algorithm: The algorithm determines which firewall responds to ARP requests. Options include IP Modulo and IP Hash.
• Session Synchronization: Session information is synchronized between the HA firewalls. In case of failover, the operational firewall can continue sessions without interruption.

Configuration Steps:

1. Enable Active/Active HA: On both firewalls, enable HA, set the mode to Active Active, and assign unique device IDs.
2. Configure Virtual Address: Define a virtual address (shared IP) on the LAN interface with the type set to ARP Load-Sharing.
3. Set Device Selection Algorithm: Choose the method for determining which firewall responds to ARP requests (IP Modulo or IP Hash).
4. Define HA Failover Conditions: Set conditions under which failover occurs, such as link or firewall failure.
5. Commit Configuration: Apply the configuration changes on both firewalls.

Additional Resources:

• Configure Active/Active HA with ARP Load-Sharing
• Configure Active/Active HA with Floating IP Addresses

sequenceDiagram
    participant A as Active Firewall
    participant P as Passive Firewall
    participant C as Client

    Note over A, P: Initial State - Active/Passive

    C->>A: Sends request
    A->>C: Responds with VIP

    Note over A, P: Failover Occurs

    C->>P: Sends request
    P->>C: Responds with VIP
  

In this diagram, the client initially communicates with the active firewall. After a failover, the passive firewall becomes active and continues to handle client requests

For detailed configuration steps and best practices, refer to the official Palo Alto Networks documentation

• Configure Active/Active HA with Floating IP Addresses
• Configure Active/Active HA with Route-Based Redundancy

Mermaid Sequence Diagram: Active/Active HA Configuration

The following Mermaid sequence diagram illustrates the interactions between two firewalls in an Active/Active High Availability (HA) configuration:

sequenceDiagram
    participant A as Active Firewall 1
    participant B as Active Firewall 2
    participant C as Client

    C->>A: Sends request
    A->>C: Responds

    C->>B: Sends request
    B->>C: Responds

    Note over A, B: Both firewalls actively process traffic
    Note over A, B: Session information is synchronized between firewalls
  

In this configuration, both firewalls handle client requests simultaneously, distributing the traffic load. Session synchronization ensures that if one firewall fails, the other can seamlessly continue processing sessions without interruption.

Choosing Between Active/Passive and Active/Active

The decision between Active/Passive and Active/Active configurations should be based on specific network requirements:

• Active/Passive: Suitable for environments where simplicity and cost-effectiveness are prioritized, and where occasional failovers are acceptable.
• Active/Active: Ideal for networks requiring high throughput and load balancing, especially when dealing with high traffic volumes and the need for continuous uptime. However, this configuration demands more complex setup and maintenance.

It's essential to assess your organization's specific needs, traffic patterns, and resource availability when designing your HA architecture to ensure optimal performance and reliability.