FortiGate-6000 and FortiGate-7000 GTP load balancing

On a FortiGate-6000 or 7000 system you can use the following command to enable or disable GTP load balancing.

config load-balance setting

config gtp-load-balance {disable | enable}

end

The following flow rule is also available to direct GTP-C traffic to the primary FPC or FPM.

config load-balance flow-rule

edit 17

set ether-type ipv4

set protocol udp

set dst-l4port 2123-2123

set comment "gtp-c to master blade"

next

end

By default, both of these configurations are disabled and GTP-C and GTP-U traffic is not load balanced. The DP processor sends all GTP-C and GTP-U traffic to the primary FPC or FPM.

To load balance GTP-U traffic to multiple FPCs or FPMs, you can set gtp-load-balance to enable. This also enables the GTP-C flow rule. GTP-U traffic is then load balanced across all FPCs or FPMs while GTP-C traffic is still handled by the primary FPC or FPM. This is the recommended configuration for load balancing GTP traffic.

GTP-U load balancing may not distribute sessions evenly among all of the FPCs or FPMs. Its common in many 4G networks to have just a few SGWs. Similar configurations with very few serves may also be used in other GTP implementations. If the FortiGate-6000 or 7000 receives GTP traffic from a very few servers, the GTP traffic will have very few source and destination IP addresses and TCP/IP ports. Since the FortiGate-6000 and 7000 perform SLBC load balancing based on source and destination IP addresses and TCP ports, its possible that sessions will not be distributed evenly among the FPCs or FPMs. In fact, most GTP-U traffic could be processed by a limited number of FPCs or FPMs.

Enabling GTP load balancing still distributes sessions and improves performance, but performance gains from enabling GTP load balancing may not be as high as anticipated.