Initial revision

arp.c

@@ -0,0 +1,56 @@
+#include <string.h>
+#include <unistd.h>
+#include <net/ethernet.h>
+#include <net/if_arp.h>
+#include <linux/if_packet.h>
+
+#include "l2tpns.h"
+
+/* Most of this code is based on keepalived:vrrp_arp.c */
+
+struct arp_buf {
+	struct ether_header eth;
+	struct arphdr arp;
+
+	/* Data bit - variably sized, so not present in |struct arphdr| */
+	unsigned char ar_sha[ETH_ALEN];	/* Sender hardware address */
+	ipt ar_sip;			/* Sender IP address. */
+	unsigned char ar_tha[ETH_ALEN]; /* Target hardware address */
+	ipt ar_tip;			/* Target ip */
+} __attribute__((packed));
+
+void sendarp(int ifr_idx, const unsigned char* mac, ipt ip)
+{
+	int fd;
+	struct sockaddr_ll sll;
+	struct arp_buf buf;
+
+	/* Ethernet */
+	memset(buf.eth.ether_dhost, 0xFF, ETH_ALEN);
+	memcpy(buf.eth.ether_shost, mac, ETH_ALEN);
+	buf.eth.ether_type = htons(ETHERTYPE_ARP);
+
+	/* ARP */
+	buf.arp.ar_hrd = htons(ARPHRD_ETHER);
+	buf.arp.ar_pro = htons(ETHERTYPE_IP);
+	buf.arp.ar_hln = ETH_ALEN;
+	buf.arp.ar_pln = 4; //IPPROTO_ADDR_LEN;
+	buf.arp.ar_op = htons(ARPOP_REQUEST);
+
+	/* Data */
+	memcpy(buf.ar_sha, mac, ETH_ALEN);
+	memcpy(&buf.ar_sip, &ip, sizeof(ip));
+	memcpy(buf.ar_tha, mac, ETH_ALEN);
+	memcpy(&buf.ar_tip, &ip, sizeof(ip));
+	
+	/* Now actually send the thing */
+	fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_RARP));
+
+	memset(&sll, 0, sizeof(sll));
+	sll.sll_family = AF_PACKET;
+	strncpy(sll.sll_addr, mac, sizeof(sll.sll_addr)); /* Null-pad */
+	sll.sll_halen = ETH_ALEN;
+	sll.sll_ifindex = ifr_idx;
+
+	sendto(fd, &buf, sizeof(buf), 0, (struct sockaddr*)&sll, sizeof(sll));
+}