Segue as regras de mangle que utilizo
PARA 2 LINKS
chain=prerouting connection-state=new nth=1,1,0 src-address-list=ADSLlista dst-address-list=!valido action=mark-connection new-connection-mark=bancos passthrough=yes
chain=prerouting connection-mark=bancos src-address-list=ADSLlista dst-address-list=!valido action=mark-routing new-routing-mark=bancos passthrough=no
chain=prerouting connection-state=new nth=1,1,1 src-address-list=ADSLlista dst-address-list=!valido action=mark-connection new-connection-mark=teste2 passthrough=yes
chain=prerouting connection-mark=teste2 src-address-list=ADSLlista dst-address-list=!valido action=mark-routing new-routing-mark=teste3 passthrough=no
PARA 3 LINKS
chain=prerouting connection-state=new nth=2,4,0 src-address-list=ADSLlista dst-address-list=!valido action=mark-connection new-connection-mark=bancosx passthrough=yes
chain=prerouting connection-mark=bancosx src-address-list=ADSLlista dst-address-list=!valido action=mark-routing new-routing-mark=bancos passthrough=no
chain=prerouting connection-state=new nth=2,4,1 src-address-list=ADSLlista dst-address-list=!valido action=mark-connection new-connection-mark=teste2x passthrough=yes
chain=prerouting connection-mark=teste2x src-aUtiliddress-list=ADSLlista dst-address-list=!valido action=mark-routing new-routing-mark=teste3 passthrough=no
chain=prerouting connection-state=new nth=2,4,2 src-address-list=ADSLlista dst-address-list=!valido action=mark-connection new-connection-mark=adsl_res2x passthrough=yes
chain=prerouting connection-mark=adsl_res2x src-address-list=ADSLlista dst-address-list=!valido action=mark-routing new-routing-mark=adsl_r2 passthrough=no
Veja que tem alguns itens a mais, mas isso não deve interferir
- Negando lista de alguns ip's válidos "=!valido"
-Definindo clientes que passarão "src-address-list=ADSLlista"
Creio que os NTH's estão corretos, e portanto imagino que somente eles poderiam alterar essa proporção