Enabling GTP load balancing
You can use the following load balancing command to enable or disable FortiGate 7000E GTP-U 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 FPM.
config load-balance flow-rule
edit 17
set status disable
set ether-type ipv4
set src-addr-ipv4 0.0.0.0 0.0.0.0
set dst-addr-ipv4 0.0.0.0 0.0.0.0
set protocol udp
set src-l4port 0-0
set dst-l4port 2123-2123
set action forward
set forward-slot master
set priority 5
set comment "gtp-c to primary blade"
next
end
The recommended configuration for optimal GTP-C tunnel setup and GTP-U throughput performance is to enable gtp-load-balance and disable the GTP-C flow rule. In this configuration, both GTP-C and GTP-U traffic is load balanced among all of the FPMs:
config load-balance setting
config gtp-load-balance enable
end
config load-balance flow-rule
edit 17
set status disable
set ether-type ipv4
set src-addr-ipv4 0.0.0.0 0.0.0.0
set dst-addr-ipv4 0.0.0.0 0.0.0.0
set protocol udp
set src-l4port 0-0
set dst-l4port 2123-2123
set action forward
set forward-slot master
set priority 5
set comment "gtp-c to primary blade"
next
end
If you want GTP-C traffic to only be processed by the primary FPM, you can edit the GTP-C flow rule and set status to enable. When enabled, this flow rule sends all GTP-C traffic to the primary FPM. Enabling this flow rule can reduce GTP performance, since all GTP-C tunnel setup sessions will be done by the primary FPM and not distributed among all of the FPMs.
config load-balance flow-rule
edit 17
set status enable
set ether-type ipv4
set src-addr-ipv4 0.0.0.0 0.0.0.0
set dst-addr-ipv4 0.0.0.0 0.0.0.0
set protocol udp
set src-l4port 0-0
set dst-l4port 2123-2123
set action forward
set forward-slot master
set priority 5
set comment "gtp-c to primary blade"
next
end
GTP-U load balancing may not distribute sessions evenly among all of the FPMs. Its common in many 4G networks to have just a few SGWs. Similar configurations with very few servers may also be used in other GTP implementations. If the FortiGate 7000E 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 SLBC load balancing is based on source and destination IP addresses and TCP ports, its possible that sessions will not be distributed evenly among the FPMs. In fact, most GTP-U traffic could be processed by a limited number of FPMs.
Enabling GTP-U load balancing still distributes sessions and improves performance, but performance gains from enabling GTP-U load balancing may not be as high as anticipated.