int dhcprelay_main(int argc UNUSED_PARAM, char **argv)
{
struct sockaddr_in server_addr;
char **iface_list;
int *fds;
int num_sockets, max_socket;
uint32_t our_nip;
INIT_G();
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
server_addr.sin_port = htons(SERVER_PORT);
/* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
if (!argv[1] || !argv[2])
bb_show_usage();
if (argv[3]) {
if (!inet_aton(argv[3], &server_addr.sin_addr))
bb_perror_msg_and_die("bad server IP");
}
iface_list = make_iface_list(argv + 1, &num_sockets);
fds = xmalloc(num_sockets * sizeof(fds[0]));
/* Create sockets and bind one to every iface */
max_socket = init_sockets(iface_list, num_sockets, fds);
/* Get our IP on server_iface */
if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
return 1;
/* Main loop */
while (1) {
// reinit stuff from time to time? go back to make_iface_list
// every N minutes?
fd_set rfds;
struct timeval tv;
int i;
FD_ZERO(&rfds);
for (i = 0; i < num_sockets; i++)
FD_SET(fds[i], &rfds);
tv.tv_sec = SELECT_TIMEOUT;
tv.tv_usec = 0;
if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
int packlen;
struct dhcp_packet dhcp_msg;
/* server */
if (FD_ISSET(fds[0], &rfds)) {
packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
if (packlen > 0) {
pass_to_client(&dhcp_msg, packlen, fds);
}
}
/* clients */
for (i = 1; i < num_sockets; i++) {
struct sockaddr_in client_addr;
socklen_t addr_size;
if (!FD_ISSET(fds[i], &rfds))
continue;
addr_size = sizeof(client_addr);
packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
(struct sockaddr *)(&client_addr), &addr_size);
if (packlen <= 0)
continue;
/* Get our IP on corresponding client_iface */
// RFC 1542
// 4.1 General BOOTP Processing for Relay Agents
// 4.1.1 BOOTREQUEST Messages
// If the relay agent does decide to relay the request, it MUST examine
// the 'giaddr' ("gateway" IP address) field. If this field is zero,
// the relay agent MUST fill this field with the IP address of the
// interface on which the request was received. If the interface has
// more than one IP address logically associated with it, the relay
// agent SHOULD choose one IP address associated with that interface and
// use it consistently for all BOOTP messages it relays. If the
// 'giaddr' field contains some non-zero value, the 'giaddr' field MUST
// NOT be modified. The relay agent MUST NOT, under any circumstances,
// fill the 'giaddr' field with a broadcast address as is suggested in
// [1] (Section 8, sixth paragraph).
// but why? what if server can't route such IP? Client ifaces may be, say, NATed!
// 4.1.2 BOOTREPLY Messages
// BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
// It is the responsibility of BOOTP servers to send BOOTREPLY messages
// directly to the relay agent identified in the 'giaddr' field.
// (yeah right, unless it is impossible... see comment above)
// Therefore, a relay agent may assume that all BOOTREPLY messages it
// receives are intended for BOOTP clients on its directly-connected
// networks.
//
// When a relay agent receives a BOOTREPLY message, it should examine
// the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
// These fields should provide adequate information for the relay agent
// to deliver the BOOTREPLY message to the client.
//
// The 'giaddr' field can be used to identify the logical interface from
// which the reply must be sent (i.e., the host or router interface
// connected to the same network as the BOOTP client). If the content
// of the 'giaddr' field does not match one of the relay agent's
// directly-connected logical interfaces, the BOOTREPLY message MUST be
// silently discarded.
if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) {
/* Fall back to our IP on server iface */
// this makes more sense!
dhcp_msg.gateway_nip = our_nip;
}
// maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
}
}
xid_expire();
} /* while (1) */
/* return 0; - not reached */
}
int main() {
make_iface_list();
}
