Solving the High Availability problem

Solving the High Availability problem

The basic high availability (HA) problem for TCP/IP networks and security gateways is keeping network traffic flowing. Uninterrupted traffic flow is a critical component for online systems and media because critical business processes quickly come to a halt when the network is down.

The security gateway is a crucial component of most networks since all traffic passes through it. A standalone network security gateway is a single point of failure that is vulnerable to any number of software or hardware problems that could compromise the device and bring all traffic on the network to a halt.

A common solution to the high availability problem is to eliminate the security gateway as single point of failure by introducing redundancy. With two or more redundant security gateways, if one fails, the remaining one or more gateways keep the traffic flowing. FortiOS provides six redundancy solutions: industry standard VRRP as well as five proprietary solutions: FortiGate Cluster Protocol (FGCP) high availability, FortiGate Session Life Support Protocol (FGSP) high availability, Session-Aware Load Balancing Clustering (SLBC), Enhanced Load Balanced Clustering (ELBC) and Content Clustering.

You can combine more than one high availability solution into a single configuration. A common reason for doing this could be to add VRRP to an FGCP or FGSP con- figuration.

A strong and flexible High availability solution is required for many mission-critical firewall and security profile applications. Each FortiOS high availability solution can be fine tuned to fit into many different network scenarios.


FortiGate Cluster Protocol (FGCP)

FGCP HA provides a solution for two key requirements of critical enterprise networking components: enhanced reliability and increased performance. Enhanced reliability is achieved through device failover protection, link failover protection and remote link failover protection. Also contributing to enhanced reliability is session failover protection for most IPv4 and IPv6 sessions including TCP, UDP, ICMP, IPsec VPN, and NAT sessions. Increased performance is achieved though active-active HA load balancing. Extended FGCP features include full mesh HA and virtual clustering. You can also fine tune the performance of the FGCP to change how a cluster forms and shares information among cluster units and how the cluster responds to failures.

When configured onto your network an FGCP cluster appears to be a single FortiGate unit operating in NAT/Route or Transparent mode and configuration synchronization allows you to configure a cluster in the same way as a standalone FortiGate unit. If a failover occurs, the cluster recovers quickly and automatically and also sends administrator notifications so that the problem that caused the failure can be corrected and any failed equipment restored.

The FGCP is compatible with most network environments and most networking equipment. While initial configuration is relatively quick and easy, a large number of tools and configuration options are available to fine tune the cluster for most situations.


FortiGate Session Life Support Protocol (FGSP)

In a network that already includes load balancing (either with load balancers or routers) for traffic redundancy, two identical FortiGate units can be integrated into the load balancing configuration using the FortiGate Session Life Support Protocol (FGSP). The external load balancers or routers can distribute sessions among the FortiGate units and the FGSP performs session synchronization of IPv4 and IPv6 TCP, UDP, ICMP, expectation, and NAT sessions to keep the session tables of both FortiGate units synchronized.

If one of the FortiGate units fails, session failover occurs and active sessions fail over to the unit that is still operating. This failover occurs without any loss of data. As well, the external load balancers or routers detect the failover and re-distribute all sessions to the unit that is still operating.

Load balancing and session failover is done by external routers or load balancers and not by the FGSP. The FortiGate units just perform session synchronization which allows session failover to occur without packet loss.

The FGSP also includes configuration synchronization, allowing you to make configuration changes once for both FortiGate units instead of requiring duplicate configuration changes on each unit. Settings that identify the FortiGate unit to the network, for example, interface IP addresses and BGP neighbor settings, are not synchronized so each FortiGate unit maintains its identity on the network. These settings must be configured separately for each FortiGate unit.

In previous versions of FortiOS the FGSP was called TCP session synchronization or standalone session synchronization. However, the FGSP has been expanded to include configuration synchronization and session synchronization of connectionless sessions, expectation sessions, and NAT sessions.



FortiGate units can function as master or backup Virtual Router Redundancy Protocol (VRRP) routers and can be quickly and easily integrated into a network that has already deployed VRRP. A FortiGate unit can be integrated into a VRRP group with any third-party VRRP devices and VRRP can provide redundancy between multiple FortiGate units.

In a VRRP configuration, when a FortiGate unit operating as the master unit fails, a backup unit takes its place and continues processing network traffic. If the backup unit is a FortiGate unit, the network continues to benefit from FortiOS security features. If the backup unit is a router, after a failure traffic will continue to flow, but FortiOS security features will be unavailable until the FortiGate unit is back on line. You can include different FortiGate models in the same VRRP group.

FortiOS supports VRRP between two or more FortiGate units and between FortiGate units and third-party routers that support VRRP. Using VRRP you can assign VRRP routers as master or backup routers. The master router processes traffic and the backup routers monitor the master router and can begin forwarding traffic if the master fails. Similar to the FGCP you can configuration VRRP between multiple FortiGate units to provide redundancy. You can also create a VRRP group with a FortiGate units and any routers that support VRRP.

In a VRRP configuration that consists of one FortiGate unit and one router, normally the FortiGate unit would be the master and all traffic would be processed by the FortiGate unit. If the FortiGate unit fails, all traffic switches to the router. Network connectivity is maintained even though FortiGate security features will be unavailable until the FortiGate unit can is back on line.


SessionAware Load Balancing Clustering (SLBC)

Session-Aware Load Balancing Clusters consist of one or more FortiControllers acting as load balancers and FortiGate-5000s and operating as workers all installed in one or two FortiGate-5000 series chassis.

SLBC clusters load balance TCP and UDP sessions. As a session-aware load balancer, the FortiController includes FortiASIC DP processors that maintain state information for all TCP and UDP sessions. The FortiASIC DP processors are capable of directing any TCP or UDP session to any worker installed in the same chassis. This session-awareness means that all TCP and UDP traffic being processed by a specific worker continues to be processed by the same worker. Session-awareness also means that more complex networking features such as network address translation (NAT), fragmented packets, complex UDP protocols, and complex protocols such as SIP that use pinholes, can be load balanced by the cluster.

For more information about SLBC see the FortiController Session-Aware Load Balancing Guide.

You cannot mix FGCP and SLBC clusters in the same FortiGate-5000 chassis.

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About Mike

Michael Pruett, CISSP has a wide range of cyber-security and network engineering expertise. The plethora of vendors that resell hardware but have zero engineering knowledge resulting in the wrong hardware or configuration being deployed is a major pet peeve of Michael's. This site was started in an effort to spread information while providing the option of quality consulting services at a much lower price than Fortinet Professional Services. Owns PacketLlama.Com (Fortinet Hardware Sales) and Office Of The CISO, LLC (Cybersecurity consulting firm).

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