Hi, I need to look up MAC address in the local network and I'm using Linux. What I do is send a ARP request with libnet, but after I send 3 requests, the cache still won't update. I use wireshark to catch the packets. From wireshark, I did get 3 ARP replays, after each of my ARP request. Does anyone know how come the ARP cache won't update?
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A:
The Linux kernel does not accept unsolicited ARP by default. Since the request was sent by your userspace application and not by the kernel, the kernel sees the reply as "unsolicited".
You can change this default in /proc/sys/net/ipv4/conf/*/arp_accept (either on a per-device basis or across all devices).
caf
2010-07-29 05:56:57
Thanks for the quick reply!!! Now I see. Still, is there another way to do it other then changing /proc/sys/net/ipv4/conf/*/arp_accept? by ioctl ?
Aitjcize
2010-07-29 06:26:02
Why do you need another way? What's wrong with that way? You can use "all" instead of * if you dont know what interface to set it on.
camh
2010-07-29 10:18:46
@Aitjcize: `/proc/sys/` is an interface to sysctl, however it is the *preferred* interface on Linux. You can change it programatically with a simple `fopen(); fprintf(); fclose();` sequence.
caf
2010-07-29 13:32:58