848d8761
From: philip+usenet@paeps.cx
SpreadTooThin wrote:
> I think this is like an arp request...
Yes. So it will only work for IPs on your local network.
> What I'm looking for is unix source code of a method to get the mac address
> of a computer given its IP / host name.
Depending on the Unix you're using, you may need to fight the kernel to be
able to do this. It may be tempting to try using a raw socket on the
interface with an address on the same network as the one you're interested in,
but you may find that the kernel will eat the answers instead of sending them
up the socket.
First you will need to find an interface on the same network as the IP you are
interested in. The SIOCGIFCONF and SIOCGIFNETMASK ioctls are probably what
you want. Example code can probably be found in any old arp implementation.
On a BSDish system -- or another system which implements BPF -- the easiest
way to send your ARP requests and get the answers will probably be to use the
BPF.
Sending your request will be a simple matter of creating an Ethernet header
and sticking an ARP behind it. Take a look at struct ether_header and struct
ether_arp. You should just be able to write that to your BPF descriptor.
Getting the replies will be a bit more interesting. A filter like this should
catch them: (not tested)
struct bpf_insn insns[] = {
BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 12),
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, ETHERTYPE_ARP, 0, 3),
BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 20),
BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, ARPOP_REPLY, 0, 1),
BPF_STMT(BPF_RET|BPF_K, sizeof(struct ether_arp) +
sizeof(struct ether_header)),
BPF_STMT(BPF_RET|BPF_K, 0),
};
Good luck. :-)
- Philip
--
Philip Paeps Please don't email any replies
philip@paeps.cx I follow the newsgroup.
Nanny could get a statue to cry on her shoulder and say what it really
thought about pigeons.
-- (Terry Pratchett, Maskerade)
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