[CentOS] Networking/routing issue

Hello,

I've been working on this for over a week. I don't think its working the way
it should.

Here's what I'm trying to do:

I have a Windstream dsl router with wireless > 192.168.1.100
|
|
Centos 6.8 server eth0  > 192.168.1.110 > gateway 192.168.1.111
                                     eth1 > 192.168.1.111 > gateway
192.168.1.100
|
|
Switch > other computers and devices > gateway 192.168.1.110

I want to send all internal traffic through 192.168.1.110, all external
traffic through 192.168.1.111, then back through 192.168.1.110.

I did an iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

Issues:

Outside connectivity for all other computers and devices only works if eth0
is also connected to the router, server works
Iptraf shows no traffic on eth1

Hope I haven't confused you as I have thoroughly confused myself.

TIA

TE Dukes