Help: the configuration of outlet cable with 3 ISP allocated.

[MengTS]

Situation: A connect-in cable from ISP, with 3 IP. The 3 IP belongs to
two different network segments with respective gateways. Several servers are
linked to LAN port.

Question: What configuration should be done to the WAN port in order to
guarantee the connections linked by this 3 IP  to work respectively?

Sorry,I'm in China,my english so bad…......

[hoba]

I'm not getting completely what you are asking for. Maybe a small diagram would help.