Access to ARP Cache

Hi all,

I have an IP Address, and I'm sure, that the corresponding MAC Address
is inside the ARP cache.
Is there a C-Function to get the MAC Address?

Regards
Dirk



=?ISO-8859-1?Q?Dirk_F=F6rster?=

Dirk Förster wrote:

> Hi all,
>
> I have an IP Address, and I'm sure, that the corresponding MAC Address
> is inside the ARP cache.
> Is there a C-Function to get the MAC Address?

Your mac address will not be in the arp cache of your computer. It only
lists the mac of other computers.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

James Knott wrote:
> Dirk Förster wrote:
>
>
>>Hi all,
>>
>>I have an IP Address, and I'm sure, that the corresponding MAC Address
>>is inside the ARP cache.
>>Is there a C-Function to get the MAC Address?
>
>
> Your mac address will not be in the arp cache of your computer. It only
> lists the mac of other computers.
>
That's right.
The IP Address I have is the next hop Address. And I know, that there
was an ARP request before.I want to read out the corresponding MAC Address.

On Mon, 10 Nov 2003 13:09:44 +0100, Dirk Förster wrote:

> James Knott wrote:
>> Dirk Förster wrote:
>>
>>
>>>Hi all,
>>>
>>>I have an IP Address, and I'm sure, that the corresponding MAC Address
>>>is inside the ARP cache.
>>>Is there a C-Function to get the MAC Address?
>>
>>
>> Your mac address will not be in the arp cache of your computer. It only
>> lists the mac of other computers.
>>
> That's right.
> The IP Address I have is the next hop Address. And I know, that there
> was an ARP request before.I want to read out the corresponding MAC Address.

Try ifconfig, arp and arping. For more info the man pages can come handy.

Rudi Swennen

Dirk Förster wrote:
> Hi all,
>
> I have an IP Address, and I'm sure, that the corresponding MAC Address
> is inside the ARP cache.
> Is there a C-Function to get the MAC Address?

See,

man 7 arp

FWIW, when looking for assistance with Linux programming tasks, the
Linux programming newsgroups and mailing lists are generally your best
bet, e.g.,

comp.os.linux.development.*

--
Jim

To reply by email, remove "link" and change "now.here" to "yahoo"
jfischer_link5809{at}now.here.com

I had a similar question and googled around until I
found the following ioctl. Hope this helps....



/* Try to find an entry in arp cache for the ip address specified */

printf("Find arp entry for IP : %s\n", ip);

sin = (struct sockaddr_in *) &arpreq.arp_pa;
memset(sin, 0, sizeof(struct sockaddr_in));
sin->sin_family = AF_INET;
ina.s_addr = inet_addr(ip);
memcpy(&sin->sin_addr, (char *)&ina, sizeof(struct in_addr));

strcpy(arpreq.arp_dev, "eth0");
arpreq.arp_ha.sa_family = AF_UNSPEC;
/*
rc = ioctl(sd, SIOCGARP, &arpreq);

if (rc < 0)
{
perror("Entry not available in cache. Sending arp req...\n");

send_arp_req(ip);

rc = ioctl(sd, SIOCGARP, &arpreq);
if (rc < 0)
{
printf("No arp reply. \n");
exit(1);
}
}
*/
send_arp_req(ip);

rc = ioctl(sd, SIOCGARP, &arpreq);
if (rc < 0)
{
printf("No arp reply. \n");
exit(1);
}

hw_addr = (unsigned char *) arpreq.arp_ha.sa_data;
printf("HWAddr found : %x:%x:%x:%x:%x:%x\n", hw_addr[0],
hw_addr[1], hw_addr[2], hw_addr[3], hw_addr[4], hw_addr[5]);

return 1;
}

void send_arp_req(char *ip_addr)
{
/* Sending the arp Request here */
}



Dirk Förster wrote:
> Hi all,
>
> I have an IP Address, and I'm sure, that the corresponding MAC Address
> is inside the ARP cache.
> Is there a C-Function to get the MAC Address?
>
> Regards
> Dirk
>