ok, vc vai criar 4 range /24 na mesma interface e setar manualmente nos devidos equipamentos.

se for links diferentes (/30) na ether1 vc vai colocar todos os ips publicos, exemplo:

100.100.100.2/30
101.101.101.2/30 ETHER1
102.102.102.2/30
103.103.103.2/30

SENDO QUE SEUS RESPECTIVOS GATEWAY SEJA FINAL XXX.XXX.XXX.1

DEPOIS CRIA OS RANGES /24 NA ETHER2

192.168.10.1/24
192.168.20.1/24 ETHER 2
192.168.30.1/24
192.168.40.1/24

VAI EM IP FIREWALL NAT

+ CHAIN= SRCNAT OUT-INTERFACE=ETHER1 ACTION=MASQUERADE

IP FIREWALL MANGLE

+ CHAIN=PREROUTING SRC-ADDRESS=192.168.10.0/24 ACTION=MARK-ROUTING NEW ROUTING MARK=LINK1

+ CHAIN=PREROUTING SRC-ADDRESS=192.168.20.0/24 ACTION=MARK-ROUTING NEW ROUTING MARK=LINK2

+ CHAIN=PREROUTING SRC-ADDRESS=192.168.30.0/24 ACTION=MARK-ROUTING NEW ROUTING MARK=LINK3

+ CHAIN=PREROUTING SRC-ADDRESS=192.168.40.0/24 ACTION=MARK-ROUTING NEW ROUTING MARK=LINK4

IP ROUTE

+ GATEWAY=100.100.100.1 ROUTING-MARK=LINK1
+ GATEWAY=101.101.101.1 ROUTING-MARK=LINK2
+ GATEWAY=102.102.102.1 ROUTING-MARK=LINK3
+ GATEWAY=103.103.103.1 ROUTING-MARK=LINK4

+ GATEWAY=100.100.100.1 COMMENT=DEFAULT

DEIXA ALGUM LINK COMO ROTA DEFAULT

IP ROUTE RULES

+ SRC-ADRRESS=192.168.10.0/24 ROUTINK-MARK=LINK1 ACTION=LOOKUP TABLE=LINK1

+ SRC-ADRRESS=192.168.20.0/24 ROUTINK-MARK=LINK2 ACTION=LOOKUP TABLE=LINK2

+ SRC-ADRRESS=192.168.30.0/24 ROUTINK-MARK=LINK3 ACTION=LOOKUP TABLE=LINK3

+ SRC-ADRRESS=192.168.40.0/24 ROUTINK-MARK=LINK4 ACTION=LOOKUP TABLE=LINK4

PRONTO JA DEVE FUNCIONAR, NAO COPIE E COLE Q NAO VAI FUNCIONAR, SIGA PASSO A PASSO PELO WINBOX, SE O GATEWAY FOR O MESMO AI JA NAO SEI TE AJUDAR NAO