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HA heartbeat and communication between cluster units

Connecting HA heartbeat interfaces

For most FortiGate models if you do not change the heartbeat interface configuration, you can isolate the default heartbeat interfaces of all of the cluster units by connecting them all to the same switch. Use one switch per heartbeat interface. If the cluster consists of two units you can connect the heartbeat interfaces together using crossover cables.

HA heartbeat and data traffic are supported on the same cluster interface. In NAT/Route mode, if you decide to use heartbeat interfaces for processing network traffic or for a management connection, you can assign the interface any IP address. This IP address does not affect HA heartbeat traffic.

In Transparent mode, you can connect the heartbeat interface to your network and enable management access. You would then establish a management connection to the interface using the Transparent mode management IP address. This configuration does not affect HA heartbeat traffic.

 

Heartbeat packets and heartbeat interface selection

HA heartbeat hello packets are constantly sent by all of the enabled heartbeat interfaces. Using these hello packets, each cluster unit confirms that the other cluster units are still operating. The FGCP selects one of the heartbeat interfaces to be used for communication between the cluster units. The FGCP selects the heartbeat interface for heartbeat communication based on the linkfail states of the heartbeat interfaces, on the priority of the heartbeat interfaces, and on the interface index.

The FGCP checks the linkfail state of all heartbeat interfaces to determine which ones are connected. The FGCP selects one of these connected heartbeat interfaces to be the one used for heartbeat communication. The FGCP selects the connected heartbeat interface with the highest priority for heartbeat communication.

If more than one connected heartbeat interface has the highest priority the FGCP selects the heartbeat interface with the lowest interface index. The web-based manager lists the FortiGate unit interfaces in alphabetical order. This order corresponds to the interface index order with lowest index at the top and highest at the bottom. If more than one heartbeat interface has the highest priority, the FGCP selects the interface that is highest in the heartbeat interface list (or first in alphabetical order) for heartbeat communication.

If the interface that is processing heartbeat traffic fails or becomes disconnected, the FGCP uses the same criteria to select another heartbeat interface for heartbeat communication. If the original heartbeat interface is fixed or reconnected, the FGCP again selects this interface for heartbeat communication.

The HA heartbeat communicates cluster session information, synchronizes the cluster configuration, synchronizes the cluster kernel routing table, and reports individual cluster member status. The HA heartbeat constantly communicates HA status information to make sure that the cluster is operating properly.

 

Interface index and display order

The web-based manager and CLI display interface names in alphanumeric order. For example, the sort order for a FortiGate unit with 10 interfaces (named port1 through port10) places port10 at the bottom of the list:

  • port1
  • port2 through 9
  • port10

 

However, interfaces are indexed in hash map order, rather than purely by alphabetic order or purely by interface number value comparisons. As a result, the list is sorted primarily alphabetical by interface name (for example, base1 is before port1), then secondarily by index numbers:

  • port1
  • port10
  • port2 through port9

 

HA heartbeat interface IP addresses

The FGCP uses link-local IP4 addresses (RFC 3927) in the 169.254.0.x range for HA heartbeat interface IP addresses and for inter-VDOM link interface IP addresses. When a cluster initially starts up, the primary unit heartbeat interface IP address is 169.254.0.1. Subordinate units are assigned heartbeat interface IP addresses in the range 169.254.0.2 to 169.254.0.63. HA inter-VDOM link interfaces on the primary unit are assigned IP addresses 169.254.0.65 and 169.254.0.66.

The ninth line of the following CLI command output shows the HA heartbeat interface IP address of the primary unit.

get system ha status

Model: 620

Mode: a-p

Group: 0

Debug: 0

ses_pickup: disable

Master:150 head_office_upper FG600B3908600825 1

Slave :150 head_office_lower FG600B3908600705 0

number of vcluster: 1 vcluster 1: work 169.254.0.1

Master:0 FG600B3908600825

Slave :1 FG600B3908600705

 

You can also use the execute traceroute command from the subordinate unit CLI to display HA heartbeat IP addresses and the HA inter-VDOM link IP addresses. For example, use execute ha manage 1 to connect to the subordinate unit CLI and then enter the following command to trace the route to an IP address on your network:

 

execute traceroute 172.20.20.10

traceroute to 172.20.20.10 (172.20.20.10), 32 hops max, 72 byte packets

1 169.254.0.1 0 ms 0 ms 0 ms

2 169.254.0.66 0 ms 0 ms 0 ms

3 172.20.20.10 0 ms 0 ms 0 ms

Both HA heartbeat and data traffic are supported on the same FortiGate interface. All heartbeat communication takes place on a separate VDOM called vsys_ha. Heartbeat traffic uses a virtual interface called port_ha in the vsys_ha VDOM. Data and heartbeat traffic use the same physical interface, but they’re logically separated into separate VDOMs.

 

Heartbeat packet Ethertypes

Normal IP packets are 802.3 packets that have an Ethernet type (Ethertype) field value of 0x0800. Ethertype values other than 0x0800 are understood as level 2 frames rather than IP packets.

By default, HA heartbeat packets use the following Ethertypes:

  • HA heartbeat packets for NAT/Route mode clusters use Ethertype 0x8890. These packets are used by cluster units to find other cluster units and to verify the status of other cluster units while the cluster is operating. You can change the Ethertype of these packets using the ha-eth-type option of the config system ha command.
  • HA heartbeat packets for Transparent mode clusters use Ethertype 0x8891. These packets are used by cluster units to find other cluster units and to verify the status of other cluster units while the cluster is operating. You can change the Ethertype of these packets using the hc-eth-type option of the config system ha command.
  • HA telnet sessions between cluster units over HA heartbeat links use Ethertype 0x8893. The telnet sessions are used to synchronize the cluster configurations. Telnet sessions are also used when an administrator uses the execute ha manage command to connect from one cluster unit CLI to another. You can change the Ethertype of these packets using the l2ep-eth-type option of the config system ha command.

Because heartbeat packets are recognized as level 2 frames, the switches and routers on your heartbeat network that connect to heartbeat interfaces must be configured to allow them. If level2 frames are dropped by these network devices, heartbeat traffic will not be allowed between the cluster units.

Some third-party network equipment may use packets with these Ethertypes for other purposes. For example, Cisco N5K/Nexus switches use Ethertype 0x8890 for some functions. When one of these switches receives Ethertype 0x8890 packets from an attached cluster unit, the switch generates CRC errors and the packets are not forwarded. As a result, FortiGate units connected with these switches cannot form a cluster.

In some cases, if the heartbeat interfaces are connected and configured so regular traffic flows but heartbeat traffic is not forwarded, you can change the configuration of the switch that connects the HA heartbeat interfaces to allow level2 frames with Ethertypes 0x8890, 0x8893, and 0x8891 to pass.

Alternatively, you can use the following CLI options to change the Ethertypes of the HA heartbeat packets:

config system ha

set ha-eth-type <ha_ethertype_4-digit_hex set hc-eth-type <hc_ethertype_4-digit_ex>

set l2ep-eth-type <l2ep_ethertype_4-digit_hex>

end

For example, use the following command to change the Ethertype of the HA heartbeat packets from 0x8890 to

0x8895 and to change the Ethertype of HA Telnet session packets from 0x8891 to 0x889f:

config system ha

set ha-eth-type 8895 set l2ep-eth-type 889f

end

 

Modifying heartbeat timing

In an HA cluster, if a cluster unit CPU becomes very busy, the cluster unit may not be able to send heartbeat packets on time. If heartbeat packets are not sent on time other units in the cluster may think that the cluster unit has failed and the cluster will experience a failover.

A cluster unit CPU may become very busy if the cluster is subject to a syn flood attack, if network traffic is very heavy, or for other similar reasons. You can use the following CLI commands to configure how the cluster times HA heartbeat packets:

config system ha

set hb-interval <interval_integer>

set hb-lost-threshold <threshold_integer>

set helo-holddown <holddown_integer>

end

 

Changing the lost heartbeat threshold

The lost heartbeat threshold is the number of consecutive heartbeat packets that are not received from another cluster unit before assuming that the cluster unit has failed. The default value is 6, meaning that if the 6 heartbeat packets are not received from a cluster unit then that cluster unit is considered to have failed. The range is 1 to 60 packets.

If the primary unit does not receive a heartbeat packet from a subordinate unit before the heartbeat threshold expires, the primary unit assumes that the subordinate unit has failed.

If a subordinate unit does not receive a heartbeat packet from the primary unit before the heartbeat threshold expires, the subordinate unit assumes that the primary unit has failed. The subordinate unit then begins negotiating to become the new primary unit.

The lower the hb-lost-threshold the faster a cluster responds when a unit fails. However, sometimes heartbeat packets may not be sent because a cluster unit is very busy. This can lead to a false positive failure detection. To reduce these false positives you can increase the hb-lost-threshold.

Use the following CLI command to increase the lost heartbeat threshold to 12:

config system ha

set hb-lost-threshold 12 end

 


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