I found out some document that said GNU/linux can't reply Gratuitous ARP request. But I used VMware to do this test.
One is CentOs 5.2(Ubuntu 8.1), another one is Windows xp.
Setup same both ip address.
Start two machines, xp will prompt me IP conflict.
whether linux kernel have fixed it?
if you answer is "yes" then I want to know How to Detection of IP conflict in Linux.

I did not understand what do you mean, but web tools may help you detect ip

Hello skiron.liu

When do you want to be notified of the conflict?

The cleanest place to detect the conflict is when a network interface is brought up because it is then that the IP address becomes known. That can happen at any time but, for the majority of systems, happens only at boot. Do you want to halt the boot process and display the error message? That could be inconvenient.

Alternatively, if you mostly work in the graphical environment, you might like the check to be done at login time and any conflict to be displayed in a window.

Best

Charles

If I only use command line how to detect it? find in /var/log/message? What are keywords that point out conflict?

Can't you create a conflict to test and then monitor the logs to see?

Does Linux detect duplicate IPs? I wasn't aware that it does so was thinking of running a script via pre-up in the interfaces file. Wouldn't work for DHCP but that's probably not what skiron.liu is looking for.

My work environment has a lot of embedded linux. all of this use to testing and development. maybe sometimes they set a IP that have been used to another Non-embedded linux server. Then only one device can contact network. At this point, I need a function to detect collision of IP that avoid wasted time to think about why it can't contact other PCs.

Hello skiron.liu

Don't apologise, you're English is fine! Easy to understand. I figure you're thinking clearly so that's a good start

Unless the embedded Linux systems are acting as servers (so need to have known IP addresses), why not use DHCP? That would solve the problem.

If that's not an option write back and say whether your CentOs 5.2 and Ubuntu 8.1 use the /etc/interfaces to control network interface configuration. That's the only one I'm familiar with.

Best

Charles

Maybe try something like this? I've never tried it.

The DHCP seems OK! But actually not.example: DHCP assign a.a.a.a to PC1. but because of some reason that I must manual set IP to my device. Suppose I just be use a.a.a.a then how?

I have seen this so I have this question about whether reply/request Gratuitous ARP in linux. If "yes", seem kernel isn't log collision. If "no", xp how to detect collision?

Tomorrow I will find two real PC make testing.

Hello skiron.liu

And thanks to win32sux for suggesting IPWatchD It looks like the perfect answer. There's a good explanation at http://ipwatchd.sourceforge.net/ipwatchd-whitepaper.pdf

Best

Charles

Thanks everyone for help me!
1)ipwatchd is a good daemon. It can send Gratuitous Arp and log collision.
2)other way that can also use "arping -I ethN X.X.X.X"(X.X.X.X is itself of IP), then see output. No collision occured if nothing output. Collision occured if show some MAC address to you.

Hello skiron.liu

Glad you found a solution. Thanks for arping (and sorry I didn't remember it and suggest it earlier).

Please mark thread solved via "Thread tools".

Best

Charles