[LARTC] Proxy Arp question

[Joseph Watson <jtwatson@datakota.com>]

Hello,

I have been digging around for a while trying to get a good understanding of 
how to configure linux to do proxy arp.  I understand the conncept well 
(there is lots of info on this), but am struggling to get a clear 
understanding of implimenting it on linux. 

First question:
Is the following possible, or does the firewall have to have a address on 
192.168.1.0/24 network??  My thought was I could add a route on eth0 to the 
192.168.1.0/24 network, and a route on eth1 to the host 192.168.1.2 and then 
turn on proxy arp.

    192.168.1.0/24
              |
   eth0: 192.168.2.1
        Firewall
   eth1: 192.168.3.1
              |
      192.168.1.2


Second question:
I have been using Shorewall as a firewall, and it comes with proxyarp 
capability.  Here is the working configuration of my firewall using proxy 
arp:

    192.168.1.0/24
              |
   eth0: 192.168.1.1
        Firewall
   eth1: 192.168.3.1
              |
      192.168.1.2

There are the following routes:
 192.168.1.2 dev eth1  scope link
 192.168.1.0/24 dev eth0  scope link

This makes sence.  Where I am confused is when I check the proxy_arp settings:

[]# cat /proc/sys/net/ipv4/conf/eth0/proxy_arp
0
[]# cat /proc/sys/net/ipv4/conf/eth1/proxy_arp
1
[]#

Why is proxy_arp not turned on for eth0??  Every howto I can find says to turn 
on proxy_arp for both interfaces.  

Thanks for any help.

-- 
Regards

Joseph Watson
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