arp proxy: "arp who-has" but no reply found

[dinh107]

Hi,

I want my machine 192.168.242.1 become a arp proxy for 192.168.242.2. I entered this command:
arp -Ds 192.168.242.2 eth0

Using arp -n, I verify that 192.168.242.2 is displayed on the list. When I try to ping from another machine to 192.168.242.2. I can see a arp who-has arrived to 192.168.242.1 but no reply found.

Anyone of you have experience about this please help me!!!!!
Thanks a lot,
Best regards,

Dinh Tran

[KenJackson]

A couple times in the distant past I thought I needed to use arp to solve some problem, but in both cases I found better solutions. So I have wondered if there are any practical problems for which arp is the best solution.

What are you trying to do?

[dinh107]

I am using an open-source application which will set my machine as an arp proxy but it doesnt work. So I try to set it manually. It doesnt work neither

[KenJackson]

OK, but you may not need to use arp. If you want one ethernet port to respond to two addresses, you can do that with the "ip" command something like this (I'm not sure of the syntax):

ip address add local 192.168.242.2/24 dev eth0 label eth0:name

If the PC has two ethernet ports and you want it to route packets from the network to another PC on the second port (maybe a wireless thing), then you need to setup forwarding in /etc/sysctl.conf and let arp work automatically:

net.ipv4.ip_forward = 1

You probably will also need to add routing entries with "route add" commands. (Check the table with "route -nr").