CentOS - Sep 2016 - 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

> -----Original Message-----
> From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On
> Behalf Of TE Dukes
> Sent: Saturday, September 3, 2016 7:31 AM
> To: 'CentOS mailing list'
> Subject: [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.
> 
[Thomas E Dukes] 
The above needs a little clarification: all external traffic through
192.168.1.111 > 192.168.1.110> all other computers and devices.
> 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
> 
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> https://lists.centos.org/mailman/listinfo/centos

On 09/03/2016 01:31 PM, TE Dukes wrote:
> 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.
As far as i understand, you have two interfaces in the same subnet.

This is usually a bad idea.

best regards
Ulf Volmer

In article <003101d205da$b35b9a20$1a12ce60$@palmettoshopper.com>,
TE Dukes <tdukes at palmettoshopper.com> wrote:
> > 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.
> > 
> [Thomas E Dukes] 
> The above needs a little clarification: all external traffic through
> 192.168.1.111 > 192.168.1.110> all other computers and devices.
Assuming your subnet mask is 255.255.255.0, you have both interfaces on the
same subnet, which won't work. You have two options:

1. Change the third number on the DSL router and on eth1, e.g. 192.168.2.100
   and 192.168.2.111

2. Change the third number on eth0 and all the other computers and devices.

Either of the above options will work. Choose whichever gives you least hassle.

You need to make sure that all of the other devices have the address of your
server's eth0 set as their default gateway. The server needs to have the
address of the router as its default gateway.

If the other devices want to get their addresses via DHCP (a good idea), you
will need to run a DHCP server on your server machine, as they will be isolated
from the router.

You will also need to make sure IP forwarding is enabled on the server.

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org