HA Links and Backup Links

The firewalls in an HA pair use HA links to synchronize data and maintain state information. Some models of the firewall have dedicated HA ports—Control link (HA1) and Data link (HA2), while others require you to use the in-band ports as HA links.
  • For firewalls with dedicated HA ports, use these ports to manage communication and synchronization between the firewalls. For details, see HA Ports on Palo Alto Networks Firewalls.
  • For firewalls without dedicated HA ports such as the PA-220 and PA-220R firewalls, as a best practice use the management port for the HA1 port, and use the dataplane port for the HA1 backup.
    For firewalls without dedicated HA ports, decide which ports to use for HA1 and HA1 backup based on your environment and understanding which are the least used and least congested. Assign HA1 to the best interface and HA1 backup to the other one.
HA peers in an HA cluster can be a combination of standalone members and HA pairs. HA cluster members use an HA4 link and HA4 backup link to perform session state syncronization. HA1 (control link), HA2 (data link), and HA3 (packet-forwarding link) are not supported between cluster members that aren’t HA pairs.
HA Links and Backup Links
Control Link
The HA1 link is used to exchange hellos, heartbeats, and HA state information, and management plane sync for routing, and User-ID information. The firewalls also use this link to synchronize configuration changes with its peer. The HA1 link is a Layer 3 link and requires an IP address.
ICMP is used to exchange heartbeats between HA peers.
Ports used for HA1—TCP port 28769 and 28260 for clear text communication; port 28 for encrypted communication (SSH over TCP).
If you enable encryption on the HA1 link, you can also Refresh HA1 SSH Keys and Configure Key Options.
Data Link
The HA2 link is used to synchronize sessions, forwarding tables, IPSec security associations and ARP tables between firewalls in an HA pair. Data flow on the HA2 link is always unidirectional (except for the HA2 keep-alive); it flows from the active or active-primary firewall to the passive or active-secondary firewall. The HA2 link is a Layer 2 link, and it uses ether type 0x7261 by default.
Ports used for HA2—The HA data link can be configured to use either IP (protocol number 99) or UDP (port 29281) as the transport, and thereby allow the HA data link to span subnets.
HA1 and HA2 Backup Links
Provide redundancy for the HA1 and the HA2 links. In-band ports can be used for backup links for both HA1 and HA2 connections when dedicated backup links are not available. Consider the following guidelines when configuring backup HA links:
  • The IP addresses of the primary and backup HA links must not overlap each other.
  • HA backup links must be on a different subnet from the primary HA links.
  • HA1-backup and HA2-backup ports must be configured on separate physical ports. The HA1-backup link uses port 28770 and 28260.
  • PA-3200 Series firewalls don’t support an IPv6 address for the HA1-backup link; use an IPv4 address.
Palo Alto Networks recommends enabling heartbeat backup (uses port 28771 on the MGT interface) if you use an in-band port for the HA1 or the HA1 backup links.
Packet-Forwarding Link
In addition to HA1 and HA2 links, an active/active deployment also requires a dedicated HA3 link. The firewalls use this link for forwarding packets to the peer during session setup and asymmetric traffic flow. The HA3 link is a Layer 2 link that uses MAC-in-MAC encapsulation. It does not support Layer 3 addressing or encryption. PA-7000 Series firewalls synchronize sessions across the NPCs one-for-one. On PA-800 Series, PA-3200 Series, and PA-5200 Series firewalls, you can configure aggregate interfaces as an HA3 link. The aggregate interfaces can also provide redundancy for the HA3 link; you cannot configure backup links for the HA3 link. On PA-3200 Series, PA-5200 Series, and PA-7000 Series firewalls, the dedicated HSCI ports support the HA3 link. The firewall adds a proprietary packet header to packets traversing the HA3 link, so the MTU over this link must be greater than the maximum packet length forwarded.
HA4 Link and HA4 Backup Link
The HA4 link and HA4 backup link perform session cache synchronization among all HA cluster members having the same cluster ID. The HA4 link between cluster members detects connectivity failures between cluster members by sending and receiving Layer 2 keepalive messages. View the status of the HA4 and HA4 backup links on the firewall dashboard.

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