Multiple Subnets on 1 ethernet LAN segment

Sum1 · 08-26-2014, 10:01 AM

I must be missing some simple part of the configuration process, but I can't find it myself.

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I have a Gentoo Server connected to LAN.
The LAN is a production environment so I want to be careful with testing some items on the Gentoo Server.
I've set up a static ip in the the /etc/conf.d/net:

Code:

config_eno1="10.10.0.1 netmask 255.255.255.0 broadcast 10.10.0.255"
routes_eno1="default via 192.168.1.1

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The dhcp server/routerbox controlling the LAN runs slackware 14.
I've added the following rules to the iptables firewall:

Code:

iptables -t filter -I INPUT -i eth1 -s 10.10.0.0/24 -j ACCEPT
iptables -t filter -I FORWARD -i eth1 -s 10.10.0.0/24 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0((eth0 is the internet-facing ethernet)) -s 10.10.0.0/24 -j MASQUERADE

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Also, in case the dhcp server is an issue, I added a 10.10.0.0/24 segment to it:

Code:

subnet 10.10.0.0 netmask 255.255.255.0 {
  range 10.10.0.1 10.10.0.100;
  }

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I've rebooted the Gentoo Server.
I've stopped and re-started dhcpd and iptables services on the Slackware router.

When I try to ping the router from Gentoo server:

Code:

connect: Network is unreachable

When I try to ping the Gentoo server from the router:

Code:

10 packets transmitted, 0 received, 100% packet loss, time 8997ms

What am I missing to get a 10.10.0.1 device to reach the internet on a LAN segment in the 192.168.1.0/24 range?

Thank you for your help.

smallpond · 08-26-2014, 12:32 PM

There are two independent subnets running on your LAN, but you have not indicated that you have anything routing packets between them. That doesn't happen by magic. Telling the Gentoo server to use 192.168.1.1 as a gateway does not tell it what interface to use. It is complaining that it has no interface on that subnet, which is true.

Sum1 · 08-26-2014, 01:04 PM

Smallpond, I appreciate your methodical prose.
Alas, I'm a little too dense to deduce the solution.

Are you saying, in addition to declaring a default gateway for ethernet device eno1, I also need to declare a path from the gateway to/through the other subnet?

Would this require "ip route add __________" on the Gentoo server?

Thank you for your time.

Sum1 · 08-26-2014, 07:59 PM

I've been doing some more googling and I think maybe you were telling me my configuration will not work.
It IS possible to route tcp/ip packets between ethernet devices on two different subnets, but you can't put an x.x.x.x address on a y.y.y.y subnet and route it anywhere.

Am I understanding correctly?
Please confirm if you have a min.
Thanks for your help.