FreeBSD and multiple gateways

Question: How to add multiple gateways to a FreeBSD?
Answer: No you can not do this (at least directly) on FreeBSD. FreeBSD don't support multiple gateways.
Workaround solution: If you have a server with 2 set of IPs and each set have there own gateway.

• First, you must select one of the gateway to be a default gateway.
• Then, You need ipfw (or any FreeBSD firewall solution),
  Check that your kernel support ipfw, if not, recompile your kernel with the following options(IPDIVERT and DUMMYNET is not required, but if you add IPFW/IPFW2 it better to also add these two options)

  #Firewall & NAT & DummyNet 
  options         IPFIREWALL
  options         IPDIVERT
  options         IPFIREWALL_DEFAULT_TO_ACCEPT
  options         IPFIREWALL_VERBOSE
  options         IPFIREWALL_VERBOSE_LIMIT=100
  options         DUMMYNET
  options         IPFW2
  

  add the following rule to your ipfw rules set.

   ipfw add rule_no fwd second_gateyway_ip ip from ip_of_this_gateway to not me
  

  For example, I have 2 ip set (10.0.0.100,10.0.0.101,10.0.0.102 for gateway 10.0.0.254) and (192.168.0.77,192.168.0.78 for gateways 192.168.0.254). I chose 10.0.0.254 as the default gateway. So, my ipfw rules are

   ipfw add 100 fwd 192.168.0.254 ip from 192.168.0.77 to not me
        ipfw add 110 fwd 192.168.0.254 ip from 192.168.0.78 to not me

Source: http://freebie.miraclenet.co.th/server/