When using IPv4, if the remote server is not yet in the ARP cache, the MAC resolution will fail and data appear to not be shared via alfred. Add a routine (modified from batctl sources) to request MAC resolution by simply sending a datagram to the discard port (UDP/9). This adds the remote MAC to the ARP cache, resulting in successful MAC resolution.

Signed-off-by: Jonathan Haws jhaws@sdl.usu.edu --- alfred.h | 1 + util.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 34 insertions(+)

diff --git a/alfred.h b/alfred.h index eecfdfd..5771483 100644 --- a/alfred.h +++ b/alfred.h @@ -213,3 +213,4 @@ uint16_t get_random_id(void); bool is_valid_ether_addr(uint8_t *addr); int ipv4_arp_request(struct interface *interface, const alfred_addr *addr, struct ether_addr *mac); +void ipv4_request_mac_resolve(const alfred_addr *addr); diff --git a/util.c b/util.c index dd3f00f..a6a98b9 100644 --- a/util.c +++ b/util.c @@ -30,6 +30,7 @@ #include <sys/ioctl.h> #include <sys/time.h> #include <time.h> +#include <unistd.h> #include "alfred.h"

int time_diff(struct timespec *tv1, struct timespec *tv2, @@ -85,6 +86,7 @@ int ipv4_arp_request(struct interface *interface, const alfred_addr *addr, { struct arpreq arpreq; struct sockaddr_in *sin; + int retries = 1;

memset(&arpreq, 0, sizeof(arpreq)); memset(mac, 0, ETH_ALEN); @@ -99,6 +101,14 @@ int ipv4_arp_request(struct interface *interface, const alfred_addr *addr, if (ioctl(interface->netsock, SIOCGARP, &arpreq) < 0) return -1;

+ while (retries-- && !(arpreq.arp_flags & ATF_COM)) { + ipv4_request_mac_resolve(addr); + usleep(200000); + + if (ioctl(interface->netsock, SIOCGARP, &arpreq) < 0) + return -1; + } + if (arpreq.arp_flags & ATF_COM) { memcpy(mac, arpreq.arp_ha.sa_data, sizeof(*mac)); } else { @@ -108,3 +118,26 @@ int ipv4_arp_request(struct interface *interface, const alfred_addr *addr,

return 0; } + +void ipv4_request_mac_resolve(const alfred_addr *addr) +{ + const struct sockaddr *sockaddr; + struct sockaddr_in inet4; + size_t sockaddr_len; + int sock; + char t = 0; + + sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); + if (sock < 0) + return; + + memset(&inet4, 0, sizeof(inet4)); + inet4.sin_family = AF_INET; + inet4.sin_port = htons(9); + inet4.sin_addr.s_addr = addr->ipv4.s_addr; + sockaddr = (const struct sockaddr *)&inet4; + sockaddr_len = sizeof(inet4); + + sendto(sock, &t, sizeof(t), 0, sockaddr, sockaddr_len); + close(sock); +}