There is no perfect way to load balancing on firewalls, so what I would suggest is two ways to achieve this :
1. Use source based routing where you can route half of your LAN to one ISP and other half to second ISP
2. Configure PBR (Policy based routing) to route one type of traffic ( e.g http, ftp etc) on one ISP and some other traffic type ( https, voip etc) on
the other ISP.
Sarab [ JNCIS-FWV , JNCIA-SEC , CCIP , CCSA ]
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