mjhjmtu

I am trying to setup a system composed by two Linux based gateways, and two Linux based boxes to communicate between the two boxes using a proxy_arp setup thru the two gateways.

In this example I am using the 12.0.0.0/24 network, because no piece of the network is going into the outside world. I think everything can be adapted to the class C setup too... Tell me if I am wrong.

Anyway, my network setup is like that:

 ++++++++++++++++++++++++++++++++++++++++ ethernet switch 1
 | |
 + eth0 + eth0
 | |
 +-----------+ +----------------+
 | 12.0.0.76 | + 12.255.255.254 +
 +-----------+ +----------------+
 Linux Box 1 Linux Gateway 1



 ++++++++++++++++++++++++++++++++++++++++ ethernet switch 2
 | |
 + eth0 + eth0
 | |
 +-----------+ +----------------+
 | 12.0.0.71 | + 12.255.255.254 +
 +-----------+ +----------------+
 Linux Box 2 Linux Gateway 2

Both Gateways are connected each other by a NULL MODEM SERIAL Cable and there is a 'socat' like program which is listening from ethernet and put the packets into serial and vice-versa. (almost like a ethernet-to-serial bridge)

All machines networks are statically configured (ifconfig):

Linux Box 1: 12.0.0.76 netmask 255.0.0.0 gateway 12.255.255.254

and

Linux Box 2: 12.0.0.71 netmask 255.0.0.0 gateway 12.255.255.254

and both

Gateways 12.255.255.254 netmask 255.0.0.0

and have proxy_arp enabled with sysctl

net.ipv4.conf.eth0.proxy_arp = 1 
net.ipv4.ip_forward = 1

Running the tcpdump -i eth0 arp on both Gateways it seems there is no ARP-Reply to the ARP Request because on the Linux Box 1 or 2, if I ping 12.0.0.76 or 12.0.0.71...

Here is the arp cache on the Linux Box 2:

$ arp -n
Address HWtype HWaddress Flags Mask Iface
12.0.0.76 (incomplete) eth0
12.255.255.254 ether 00:1b:c5:08:d4:11 C eth0

So I suppose the proxy_arp on 00:1b:c5:08:d4:11 (Gatway 2) DOES NOT WORK.

My goal is to reach the Linux Box 1 from Linux Box 2 and vice-versa (using proxy_arp) for example:

Linux Box 1:

$ mycommand-server listening on port 5020

Linux Box 2:

$ mycommand-client 12.0.0.76 port 5020