Fixed a stx err

[6bed4] / 6bed4router.c

/* 6bed4/router.c -- traffic forwarding daemon for public TSP service
 *
 * This is an implementation of the profile that makes TSP service publicly
 * usable, that is without authentication.  However to avoid abuse of such
 * a service, it is not anonymous -- IPv6 addresses contain the IPv4 address
 * and port.
 *
 * This is an implementation of neighbour and router discovery over a
 * tunnel that packs IPv6 inside UDP/IPv4.  This tunnel mechanism is
 * targeted specifically at embedded devices that are to function on
 * any network, including IPv4-only, while being designed as IPv6-only
 * devices with a fallback to this tunnel.
 *
 * Interestingly, as a side-effect of this design the router daemon can be
 * stateless.  Any further requirements that are stateful are most likely
 * filtering, and that can be solved in stateful firewall configuration.
 *
 * The intention of TSP is to enable IPv4-only hosts to connecto to
 * IPv6 services; the public TSP profile adds to that the ability to
 * do it in a temporary manner.
 *
 * TODO: Should we translate ICMPv4 --> ICMPv6?
 *
 * From: Rick van Rein <rick@openfortress.nl>
 */


#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <stdbool.h>

#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <getopt.h>
#include <fcntl.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>
#include <sys/ioctl.h>

#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip6.h>
#include <netinet/udp.h>
#include <netinet/icmp6.h>
#include <arpa/inet.h>

#include <linux/if.h>
#include <linux/if_tun.h>
#include <linux/if_ether.h>


/* The following will initially fail, due to an IANA obligation to avoid
 * default builds with non-standard options.
 */
#include "nonstd.h"


#define MTU 1280

/*
 * The HAVE_SETUP_TUNNEL variable is used to determine whether absense of
 * the -t option leads to an error, or to an attempt to setup the tunnel.
 * The setup_tunnel() function used for that is defined per platform, such
 * as for LINUX.  Remember to maintain the manpage's optionality for -t.
 */
#undef HAVE_SETUP_TUNNEL


/* Global variables */

char *program;

int v4sox = -1;
int v6sox = -1;

char *v4server = NULL;
char *v6server = NULL;
char *v6prefix = NULL;

const uint8_t v6listen_linklocal [16] = { 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
uint8_t v6listen_linklocal_complete [16] = { 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };

uint8_t lladdr_6bed4 [6];

struct sockaddr_in  v4name;
struct sockaddr_in6 v6name;

struct in6_addr v6listen;
struct in6_addr v6listen_complete;
struct in_addr  v4listen;


struct {
        struct tun_pi tun;
        union {
                struct {
                        struct ip6_hdr v6hdr;
                        uint8_t data [MTU - sizeof (struct ip6_hdr)];
                } idata;
                struct {
                        struct ip6_hdr v6hdr;
                        struct icmp6_hdr v6icmphdr;
                } ndata;
        } udata;
} v4data6;

#define v4tunpi6        ( v4data6.tun)
#define v4data          ((uint8_t *) &v4data6.udata)
#define v4hdr6          (&v4data6.udata.idata.v6hdr)
#define v4src6          (&v4data6.udata.idata.v6hdr.ip6_src)
#define v4dst6          (&v4data6.udata.idata.v6hdr.ip6_dst)

#define v4v6plen        ( v4data6.udata.ndata.v6hdr.ip6_plen)
#define v4v6nexthdr     ( v4data6.udata.ndata.v6hdr.ip6_nxt)
#define v4v6hoplimit    ( v4data6.udata.ndata.v6hdr.ip6_hops)

#define v4icmp6         (&v4data6.udata.ndata.v6icmphdr)
#define v4v6icmpdata    ( v4data6.udata.ndata.v6icmphdr.icmp6_data8)
#define v4v6icmptype    ( v4data6.udata.ndata.v6icmphdr.icmp6_type)
#define v4v6icmpcode    ( v4data6.udata.ndata.v6icmphdr.icmp6_code)
#define v4v6icmpcksum   ( v4data6.udata.ndata.v6icmphdr.icmp6_cksum)

#define v4ngbsoltarget  (&v4data6.udata.ndata.v6icmphdr.icmp6_data8 [4])


struct {
        struct tun_pi tun;
        union {
                uint8_t data [MTU];
                struct ip6_hdr v6hdr;
                struct icmp6_hdr v6icmp;
        } udata;
        uint8_t zero;
} v6data6;

#define v6tuncmd        ( v6data6.tun)
#define v6data          ( v6data6.udata.data)
#define v6hdr6          (&v6data6.udata.v6hdr)
#define v6src6          (&v6data6.udata.v6hdr.ip6_src)
#define v6dst6          (&v6data6.udata.v6hdr.ip6_dst)
#define v6hoplimit      ( v6data6.udata.v6hdr.ip6_hops)

#define v6nexthdr       ( v6data6.udata.v6hdr.ip6_nxt)
#define v6icmptype      ( v6data6.udata.v6icmp.icmp6_type)


uint8_t router_linklocal_address [] = {
        0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x00,
};

uint8_t democlient_linklocal_address [] = {
        0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x01,
};

uint8_t allnodes_linklocal_address [] = {
        0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x01,
};

uint8_t allrouters_linklocal_address [] = {
        0xff, 0x02, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x00, 0x02,
};

void addr_6bed4(struct in6_addr *dst_ip6, uint8_t *s_addr, int sin_port, int lanip) {

        dst_ip6->s6_addr [8] = s_addr [0] & 0xfc;
        memcpy (&dst_ip6->s6_addr [9], s_addr + 1, 3);
        dst_ip6->s6_addr [12] = sin_port >> 8;
        dst_ip6->s6_addr [13] = sin_port & 0xff;
        dst_ip6->s6_addr [14] = (s_addr [0] & 0x03) << 6 | lanip >> 8;
        dst_ip6->s6_addr [15] = lanip & 0xff;
}

/*
 *
 * Driver routines
 *
 */

#ifdef LINUX
#define HAVE_SETUP_TUNNEL
/* Implement the setup_tunnel() command for Linux.
 * Return 1 on success, 0 on failure.
 */
int setup_tunnel (void) {
        v6sox = open ("/dev/net/tun", O_RDWR);
        if (v6sox == -1) {
                fprintf (stderr, "%s: Failed to access tunnel driver on /dev/net/tun: %s\n", program, strerror (errno));
                return 0;
        }
        int ok = 1;
        struct ifreq ifreq;
        memset (&ifreq, 0, sizeof (ifreq));
        strncpy (ifreq.ifr_name, "6bed4", IFNAMSIZ);
        ifreq.ifr_flags = IFF_TUN;
        if (ok && (ioctl (v6sox, TUNSETIFF, (void *) &ifreq) == -1)) {
                ok = 0;
        }
        ifreq.ifr_name [IFNAMSIZ] = 0;
        char cmd [512+1];
        snprintf (cmd, 512, "/sbin/ip -6 addr flush dev %s", ifreq.ifr_name);
        if (ok && system (cmd) != 0) {
                ok = 0;
        }
        snprintf (cmd, 512, "/sbin/ip addr add fe80::0 dev %s scope link", ifreq.ifr_name);
        if (ok && system (cmd) != 0) {
                ok = 0;
        }
        snprintf (cmd, 512, "/sbin/ip -6 addr add %s dev %s", v6prefix, ifreq.ifr_name);
        if (ok && system (cmd) != 0) {
                ok = 0;
        }
        snprintf (cmd, 512, "/sbin/ip link set %s up mtu 1280", ifreq.ifr_name);
        if (ok && system (cmd) != 0) {
                ok = 0;
        }
        if (!ok) {
                close (v6sox);  /* This removes the tunnel interface */
        }
        return ok;
}
#endif /* LINUX */


/*
 *
 * Utility functions
 *
 */


/* Calculate the ICMPv6 checksum field
 */
uint16_t icmp6_checksum (size_t payloadlen) {
        uint16_t plenword = htons (payloadlen);
        uint16_t nxthword = htons (IPPROTO_ICMPV6);
        uint16_t *area [] = { (uint16_t *) v4src6, (uint16_t *) v4dst6, &plenword, &nxthword, (uint16_t *) v4icmp6, (uint16_t *) v4v6icmpdata };
        uint8_t areawords [] = { 8, 8, 1, 1, 1, payloadlen/2 - 2 };
        uint32_t csum = 0;
        u_int8_t i, j;
        for (i=0; i < 6; i++) {
                for (j=0; j<areawords [i]; j++) {
                        csum += ntohs (area [i] [j]);
                }
        }
        csum = (csum & 0xffff) + (csum >> 16);
        csum = (csum & 0xffff) + (csum >> 16);
        csum = htons (~csum);
        return csum;
}


/* Send an ICMPv6 reply.  This is constructed at the tunnel end, from
 * the incoming message.  The parameter indicates how many bytes the
 * ICMPv6 package counts after the ICMPv6 header.  It must be 4 (mod 8).
 *
 * Actions: v4/udp src becomes dest, set v4/udp/v6 src, len, cksum, send.
 *          v6 dest is provided (usually v4src6) but if it starts with
 *          0x00,0x00 it will be replaced with allnodes_linklocal_address.
 */
void icmp6_reply (size_t icmp6bodylen, struct in6_addr *dest) {
        v4v6hoplimit = 255;
        if ((icmp6bodylen & 0x07) != 4) {
                return;   /* illegal length, drop */
        }
        v4v6plen = htons (icmp6bodylen + 4);
        if ((* (uint16_t *) dest) == htons (0x0000)) {
                memcpy (v4dst6, allnodes_linklocal_address, 16);
        } else {
                memcpy (v4dst6, dest, 16);
        }
        memcpy (v4src6, router_linklocal_address, 16);
        v4v6icmpcksum = icmp6_checksum (ntohs (v4v6plen));
        //
        // Send the message to the IPv4 originator port
printf ("Sending ICMPv6-IPv6-UDP-IPv4 to %d.%d.%d.%d:%d, result = %zd\n",
((uint8_t *) &v4name.sin_addr.s_addr) [0],
((uint8_t *) &v4name.sin_addr.s_addr) [1],
((uint8_t *) &v4name.sin_addr.s_addr) [2],
((uint8_t *) &v4name.sin_addr.s_addr) [3],
ntohs (v4name.sin_port),
        sendto (v4sox,
                        v4data,
                        sizeof (struct ip6_hdr) + 4 + icmp6bodylen,
                        MSG_DONTWAIT,
                        (struct sockaddr *) &v4name, sizeof (v4name)));
}


/* Append the current prefix to an ICMPv6 message.  Incoming optidx
 * and return values signify original and new offset for ICMPv6 options.
 * The endlife parameter must be set to obtain zero lifetimes, thus
 * instructing the tunnel client to stop using an invalid prefix.
 */
size_t icmp6_prefix (size_t optidx, uint8_t endlife) {
        v4v6icmpdata [optidx++] = 3;    // Type
        v4v6icmpdata [optidx++] = 4;    // Length
        v4v6icmpdata [optidx++] = 64;   // This is a /64 prefix
        v4v6icmpdata [optidx++] = 0xc0; // L=1, A=1, Reserved1=0
        memset (v4v6icmpdata + optidx, endlife? 0x00: 0xff, 8);
        optidx += 8;
                                        // Valid Lifetime: Zero / Infinite
                                        // Preferred Lifetime: Zero / Infinite
        memset (v4v6icmpdata + optidx, 0, 4);
        optidx += 4;
                                        // Reserved2=0
        memcpy (v4v6icmpdata + optidx + 0, &v6listen, 8);
        memset (v4v6icmpdata + optidx + 8, 0, 8);
        optidx += 16;
        return optidx;
}


/*
 * TODO: DEPRECATED
 *
 * Append a Destination Link-Layer Address Option to an ICMPv6
 * message.  The address is comprised from the remote's UDP port
 * and IPv4 address, as seen by the router.  They are supplied
 * in that order, in network byte order.  The resulting address
 * is 6 bytes, but even though that makes it look like a MAC
 * address, it really is another beast.
 * Note that no effort is made in the router to recognise the
 * "illegal port number" 0x3333 -- the client needs a message
 * and will recognise it and act on it.
 */
size_t icmp6_dest_linkaddr (size_t optidx) {
        uint8_t typelen [2] = { ND_OPT_DESTINATION_LINKADDR, 1 };
        memcpy (v4v6icmpdata + optidx + 0, &typelen, 2);
        v4v6icmpdata [optidx + 2] = ntohs (v4name.sin_port) & 0xff;
        v4v6icmpdata [optidx + 3] = ntohs (v4name.sin_port) >> 8;
        memcpy (v4v6icmpdata + optidx + 4, &v4name.sin_addr, 4);
        optidx += 8;
        return optidx;
}


/*
 * Test if an address is a local override.  This function is compiled-in
 * to support hosts with a /64 from their own ISP and nothing more; they
 * need to access local IPv6 addresses.  We rely on the 6bed4 port being
 * 0 to decide that an address cannot be anything but a local override.
 * Define LOCAL_OVERRIDES_PORT0 to enable this feature.
 */
#ifdef LOCAL_OVERRIDES_PORT0
static inline bool is_local_override (struct in6_addr *ip6) {
        return ip6->s6_addr16 [6] == 0;
}
#else
#define is_local_override(_) false
#endif

/*
 * Test if the provided IPv6 address matches the prefix used for 6bed4.
 */
static inline bool is_6bed4 (struct in6_addr *ip6) {
        return memcmp (&v6listen, ip6->s6_addr, 8) == 0;
}


/*
 * Validate the originator's IPv6 address.  It should match the
 * UDP/IPv4 coordinates of the receiving 6bed4 socket.  Also,
 * the /64 prefix must match that of v6listen.
 */
bool validate_originator (struct sockaddr_in *sin, struct in6_addr *ip6) {
        uint16_t port = ntohs (sin->sin_port);
        uint32_t addr = ntohl (sin->sin_addr.s_addr);

        if (!is_6bed4 (ip6)) {
                return false;
        }
        if ((port & 0xff) != ip6->s6_addr [13]) {
                return false;
        }
        if ((port >> 8) != ip6->s6_addr [12]) {
                return false;
        }
        if (addr != ((ntohl(ip6->s6_addr32 [2]) & 0xfcffffff) | (((uint32_t) ip6->s6_addr [14] & 0xc0) << 18))) {
                return false;
        }
        return true;
}


/*
 * Major packet processing functions
 */


/*
 * Respond to a Router Solicitation received over the 6bed4 Network.
 */
void handle_6bed4_router_solicit (void) {
        struct in6_addr observed;
        v4v6icmptype = ND_ROUTER_ADVERT;
        v4v6icmpdata [0] = 0;                   // Cur Hop Limit: unspec
        v4v6icmpdata [1] = 0x18;                // M=0, O=0
                                                // H=0, Prf=11=Low
                                                // Reserved=0
// TODO: wire says 0x44 for router_adv.flags
        size_t writepos = 2;
        memset (v4v6icmpdata+writepos, 0xff, 2+4+4);
                                        // Router Lifetime: max, 18.2h
                                        // Reachable Time: max
                                        // Retrans Timer: max
        writepos += 2+4+4;
        writepos = icmp6_prefix (writepos, 0);
        //TODO:DEPRECATED// writepos = icmp6_dest_linkaddr (writepos);
        memcpy (&observed, v6listen_linklocal, 8);
        addr_6bed4(&observed, (uint8_t *) &v4name.sin_addr.s_addr, ntohs(v4name.sin_port), 1);
        icmp6_reply (writepos, &observed);
}


/* Handle the IPv4 message pointed at by msg as a neighbouring command.
 *
 * Type Code    ICMPv6 meaning                  Handling
 * ---- ----    -----------------------------   ----------------------------
 * 133  0       Router Solicitation             Send Router Advertisement
 * 134  0       Router Advertisement            Ignore
 * 135  0       Neighbour Solicitation          Send Neighbour Advertisement
 * 136  0       Neighbour Advertisement         Ignore
 * 137  0       Redirect                        Ignore
 */
void handle_4to6_nd (ssize_t v4ngbcmdlen) {
        uint16_t srclinklayer;
        if (v4ngbcmdlen < sizeof (struct ip6_hdr) + sizeof (struct icmp6_hdr)) {
                return;
        }
        if (v4v6icmpcode != 0) {
                return;
        }
        if (icmp6_checksum (v4ngbcmdlen - sizeof (struct ip6_hdr)) != v4v6icmpcksum) {
                return;
        }
        //
        // Approved.  Perform neighbourly courtesy.
        switch (v4v6icmptype) {
        case ND_ROUTER_SOLICIT:
                //
                // Validate Router Solicitation
                srclinklayer = 0;
                if (v4ngbcmdlen == sizeof (struct ip6_hdr) + 8 + 8) {
                        // One option is possible, the source link-layer address
                        if (v4v6icmpdata [4] != 1 || v4v6icmpdata [5] != 1) {
                                break;   /* bad opton, ignore */
                        }
                        // The source link-layer address is end-aligned
                        srclinklayer = (v4v6icmpdata [10] << 8) | v4v6icmpdata [11];
                        if (srclinklayer == 0) {
                                break;   /* illegal, ignore */
                        }
                } else if (v4ngbcmdlen == sizeof (struct ip6_hdr) + 8) {
                        srclinklayer = 0;   /* set for latter filling */
                } else {
                        break;   /* illegal length, drop */
                }
                //
                // Having accepted the Router Advertisement, respond
                handle_6bed4_router_solicit ();
                break;
        case ND_NEIGHBOR_SOLICIT:
                //
                // Validate Neigbour Solicitation
                if (!validate_originator (&v4name, v4src6)) {
                        break;  /* bad source address, drop */
                }
                if ((v4ngbcmdlen != sizeof (struct ip6_hdr) + 24) &&
                    (v4ngbcmdlen != sizeof (struct ip6_hdr) + 24 + 8)) {
                        break;   /* funny length, drop */
                }
                if ((memcmp (v4ngbsoltarget, v6listen_linklocal, 16) != 0) &&
                    (memcmp (v4ngbsoltarget, v6listen_linklocal_complete, 16) != 0) &&
                    (memcmp (v4ngbsoltarget, &v6listen_complete, 16) != 0)) {
                        break;  /* target not known here, drop */
                }
                //
                // Construct Neigbour Advertisement
                v4v6icmptype = ND_NEIGHBOR_ADVERT;
                v4v6icmpdata [0] = 0xc0;
                v4v6icmpdata [1] =
                v4v6icmpdata [2] =
                v4v6icmpdata [3] = 0x00;        // R=1, S=1, O=1, Reserved=0
                memcpy (v4v6icmpdata +  4, &v6listen_complete, 16);
                // Append option: the target link-layer address
                // Note: wire does not include target link-layer address
                v4v6icmpdata [20] = 2;          // Type: Target Link-Layer Addr
                v4v6icmpdata [21] = 1;          // Length: 1x 8 bytes
                memcpy (v4v6icmpdata + 22, lladdr_6bed4, 6);
                icmp6_reply (28, v4src6);       // 28 is the ICMPv6 response length
                break;
        case ND_ROUTER_ADVERT:
        case ND_NEIGHBOR_ADVERT:
        case ND_REDIRECT:
                break;   /* drop */
        }
}


/* 
 * Forward a message received over the 6bed4 Network over IPv6.
 * Note that existing checksums will work well, as only the
 * Hop Limit has been altered, and this is not part of the
 * checksum calculations.
 */
void handle_4to6_plain_unicast (ssize_t v4datalen) {
printf ("Writing IPv6, result = %zd\n",
        write (v6sox, &v4data6, sizeof (struct tun_pi) + v4datalen));
}


/*
 * Forward a 6bed4 message to another 6bed4 destination address.
 * Note that existing checksums will work well, as only the
 * Hop Limit has been altered, and this is not part of the
 * checksum calculations.
 */
void relay_6bed4_plain_unicast (uint8_t* data, ssize_t v4datalen, struct in6_addr *ip6) {
        v4name.sin_port = htons (ip6->s6_addr [12] << 8 | ip6->s6_addr [13]);
        uint8_t *addr = (uint8_t *) &v4name.sin_addr.s_addr;
        addr [0] = (ip6->s6_addr [8] & 0xfc) | ip6->s6_addr [14] >> 6;
        memcpy (addr + 1, ip6->s6_addr + 9, 3);
printf ("Relaying over 6bed4 Network to %d.%d.%d.%d:%d, result = %zd\n",
((uint8_t *) &v4name.sin_addr.s_addr) [0],
((uint8_t *) &v4name.sin_addr.s_addr) [1],
((uint8_t *) &v4name.sin_addr.s_addr) [2],
((uint8_t *) &v4name.sin_addr.s_addr) [3],
ntohs (v4name.sin_port),
        sendto (v4sox,
                        data, v4datalen,
                        MSG_DONTWAIT,
                        (struct sockaddr *) &v4name, sizeof (v4name)));
}


/* Receive a tunnel package, and route it to either the handler for the
 * tunnel protocol, or to the handler that checks and then unpacks the
 * contained IPv6.
 */
void handle_4to6 (void) {
        uint8_t buf [1501];
        ssize_t buflen;
        socklen_t adrlen = sizeof (v4name);
        //
        // Receive IPv4 package, which may be tunneled or a tunnel request
        buflen = recvfrom (v4sox,
                        v4data, MTU,
                        MSG_DONTWAIT,
                        (struct sockaddr *) &v4name, &adrlen
                );
        if (buflen == -1) {
                printf ("%s: Error receiving IPv4-side package: %s",
                                program, strerror (errno));
                return;
        }
        if (buflen < sizeof (struct ip6_hdr)) {
                return;
        }
        if ((v4data [0] & 0xf0) != 0x60) {
                // Not an IPv6 packet
                return;
        }
        //
        // Handle the tunneled IPv6 package (dependent on its class)
        if ((v4v6nexthdr == IPPROTO_ICMPV6) &&
                        (v4v6icmptype >= 133) && (v4v6icmptype <= 137)) {
                //
                // Not Plain: Router Adv/Sol, Neighbor Adv/Sol, Redirect
                if (v4v6hoplimit != 255) {
                        return;
                }
                handle_4to6_nd (buflen);
        } else if ((v4dst6->s6_addr [0] != 0xff) && !(v4dst6->s6_addr [8] & 0x01)) {
                //
                // Plain Unicast
                if (is_local_override (v4dst6)) {
                        handle_4to6_plain_unicast (buflen);
                } else if (validate_originator (&v4name, v4src6)) {
                        if (v4v6hoplimit-- <= 1) {
                                return;
                        }
                        if (is_6bed4 (v4dst6)) {
                                relay_6bed4_plain_unicast (v4data, buflen, v4dst6);
                        } else {
                                handle_4to6_plain_unicast (buflen);
                        }
                } else if (is_6bed4 (v4src6)) {
                        // The sender must not have kept NAT/firewall holes
                        // open and should be instructed about a change in
                        // its 6bed4 Link-Local Address.
                        handle_6bed4_router_solicit ();
                }
        } else {
                //
                // Plain Multicast
                //OPTIONAL// validate_originator, hoplimit, relay_mcast.
                return;
        }
}


/* Receive an IPv6 package, check its address and pickup IPv4 address and
 * port, then package it as a tunnel message and forward it to IPv4:port.
 */
void handle_6to4 (void) {
        //
        // Receive the IPv6 package and ensure a consistent size
        size_t rawlen = read (v6sox, &v6data6, sizeof (v6data6));
        if (rawlen == -1) {
                return;         /* error reading, drop */
        }
        if (rawlen < sizeof (struct tun_pi) + sizeof (struct ip6_hdr) + 1) {
                return;         /* too small, drop */
        }
        if (v6tuncmd.proto != htons (ETH_P_IPV6)) {
                return;         /* no IPv6, drop */
        }
        if ((v6nexthdr == IPPROTO_ICMPV6) &&
                        (v6icmptype >= 133) && (v6icmptype <= 137)) {
                return;         /* not plain IPv6, drop */
        }
        if (v6hoplimit-- <= 1) {
                // TODO: Send back an ICMPv6 error message
                return;         /* hop limit exceeded, drop */
        }
        if ((v6dst6->s6_addr [0] == 0xff) /* TODO:UDP_PORT_NOT_YET_FORCED_TO_EVEN || (v6dst6->s6_addr [8] & 0x01) */ ) {
printf ("Received multicast IPv6 data, flags=0x%04x, proto=0x%04x\n", v6tuncmd.flags, v6tuncmd.proto);
                //OPTIONAL// handle_6to4_plain_multicast ()
                return;         /* multicast, drop */
        }
printf ("Received plain unicast IPv6 data, flags=0x%04x, proto=0x%04x\n", v6tuncmd.flags, v6tuncmd.proto);
        //
        // Ensure that the incoming IPv6 address is properly formatted
        // Note that this avoids access to ::1/128, fe80::/10, fec0::/10
        if (memcmp (v6dst6, &v6listen, 8) != 0) {
                return;
        }
        //
        // Harvest socket address data from destination IPv6, then send
        relay_6bed4_plain_unicast (v6data, rawlen - sizeof (struct tun_pi), v6dst6);
}


/* Run the daemon core code, passing information between IPv4 and IPv6 and
 * responding to tunnel requests if so requested.
 */
void run_daemon (void) {
        fd_set io;
        FD_ZERO (&io);
        FD_SET (v4sox, &io);
        FD_SET (v6sox, &io);
        int nfds = (v4sox < v6sox)? (v6sox + 1): (v4sox + 1);
        while (1) {
                select (nfds, &io, NULL, NULL, NULL);
                if (FD_ISSET (v4sox, &io)) {
                        handle_4to6 ();
                } else {
                        FD_SET (v4sox, &io);
                }
                if (FD_ISSET (v6sox, &io)) {
                        handle_6to4 ();
                } else {
                        FD_SET (v6sox, &io);
                }
fflush (stdout);
        }
}


/* Option descriptive data structures */

char *short_opt = "l:L:t:h";

struct option long_opt [] = {
        { "v4listen", 1, NULL, 'l' },
        { "v6prefix", 1, NULL, 'L' },
        { "tundev", 1, NULL, 't' },
        { "help", 0, NULL, 'h' },
        { NULL, 0, NULL, 0 }    /* Array termination */
};

/* Parse commandline arguments (and start to process them).
 * Return 1 on success, 0 on failure.
 */
int process_args (int argc, char *argv []) {
        int ok = 1;
        int help = (argc == 1);
        int done = 0;
        while (!done) {
                switch (getopt_long (argc, argv, short_opt, long_opt, NULL)) {
                case -1:
                        done = 1;
                        if (optind != argc) {
                                fprintf (stderr, "%s: Extra arguments not permitted: %s...\n", program, argv [optind]);
                                ok = 0;
                        }
                        break;
                case 'l':
                        if (v4sox != -1) {
                                ok = 0;
                                fprintf (stderr, "%s: Only one -l argument is permitted\n", program);
                                break;
                        }
                        v4server = optarg;
                        if (inet_pton (AF_INET, optarg, &v4name.sin_addr) <= 0) {
                                ok = 0;
                                fprintf (stderr, "%s: Failed to parse IPv4 address %s\n", program, optarg);
                                break;
                        }
                        memcpy (&v4listen, &v4name.sin_addr, 4);
                        v4sox = socket (AF_INET, SOCK_DGRAM, 0);
                        if (v4sox == -1) {
                                ok = 0;
                                fprintf (stderr, "%s: Failed to allocate UDPv4 socket: %s\n", program, strerror (errno));
                                break;
                        }
                        if (bind (v4sox, (struct sockaddr *) &v4name, sizeof (v4name)) != 0) {
                                ok = 0;
                                fprintf (stderr, "%s: Failed to bind to UDPv4 %s:%d: %s\n", program, optarg, ntohs (v4name.sin_port), strerror (errno));
                                break;
                        }
                        break;
                case 'L':
                        if (v6server) {
                                ok = 0;
                                fprintf (stderr, "%s: Only one -L argument is permitted\n", program);
                                break;
                        }
                        char *slash64 = strchr (optarg, '/');
                        if (!slash64 || strcmp (slash64, "/64") != 0) {
                                ok = 0;
                                fprintf (stderr, "%s: The -L argument must be an explicit /64 prefix and not %s\n", program, slash64? slash64: "implied");
                                break;
                        }
                        *slash64 = 0;
                        v6server = strdup (optarg);
                        *slash64 = '/';
                        v6prefix = optarg;
                        if (!v6server || inet_pton (AF_INET6, v6server, &v6listen) <= 0) {
                                ok = 0;
                                fprintf (stderr, "%s: Failed to parse IPv6 prefix %s\n", program, optarg);
                                break;
                        }
                        if (v6listen.s6_addr32 [2] || v6listen.s6_addr32 [3]) {
                                ok = 0;
                                fprintf (stderr, "%s: IPv6 prefix contains bits beyond its /64 prefix: %s\n", program, optarg);
                                break;
                        }
                        break;
                case 't':
                        if (v6sox != -1) {
                                ok = 0;
                                fprintf (stderr, "%s: Multiple -t arguments are not permitted\n", program);
                                break;
                        }
                        v6sox = open (optarg, O_RDWR);
                        if (v6sox == -1) {
                                ok = 0;
                                fprintf (stderr, "%s: Failed to open tunnel device %s: %s\n", program, optarg, strerror (errno));
                                break;
                        }
                        break;
                default:
                        ok = 0;
                        help = 1;
                        /* continue into 'h' to produce usage information */
                case 'h':
                        help = 1;
                        break;
                }
                if (help || !ok) {
                        done = 1;
                }
        }
        if (help) {
#ifdef HAVE_SETUP_TUNNEL
                fprintf (stderr, "Usage: %s [-t /dev/tunX] -l <v4server> -L <v6prefix>/64\n       %s -h\n", program, program);
#else
                fprintf (stderr, "Usage: %s -t /dev/tunX -l <v4server> -L <v6prefix>/64\n       %s -h\n", program, program);
#endif
                return ok;
        }
        if (!ok) {
                return 0;
        }
        if (v4sox == -1) {
                fprintf (stderr, "%s: Use -l to specify an IPv4 address for the tunnel interface\n", program);
                return 0;
        }
        if (!v6server) {
                fprintf (stderr, "%s: Use -L to specify a /64 prefix on the IPv6 side\n", program);
                return 0;
        }
#ifdef HAVE_SETUP_TUNNEL
        if (v6sox == -1) {
                if (geteuid () != 0) {
                        fprintf (stderr, "%s: You should be root, or use -t to specify an accessible tunnel device\n", program);
                        return 0;
                }
                ok = setup_tunnel ();
        }
#else /* ! HAVE_SETUP_TUNNEL */
        if (v6sox == -1) {
                fprintf (stderr, "%s: You must specify a tunnel device with -t that is accessible to you\n", program);
                return 0;
        }
#endif /* HAVE_SETUP_TUNNEL */
        return ok;
}


/* The main program parses commandline arguments and forks off the daemon
 */
int main (int argc, char *argv []) {
        //
        // Initialise
        program = argv [0];
        memset (&v4name, 0, sizeof (v4name));
        memset (&v6name, 0, sizeof (v6name));
        v4name.sin_family  = AF_INET ;
        v6name.sin6_family = AF_INET6;
        v4name.sin_port = htons (UDP_PORT_6BED4);   /* 6BED4 standard port */
        v4tunpi6.flags = 0;
        v4tunpi6.proto = htons (ETH_P_IPV6);
        //
        // Parse commandline arguments
        if (!process_args (argc, argv)) {
                exit (1);
        }
        //
        // Setup a few addresses for later comparison/reproduction
        //  * lladdr_6bed4 is the 6bed4 Link-Local Address
        //  * v6listen_complete is the router's full IPv6 address (with if-id)
        //  * v6listen_linklocal_complete is fe80::/64 plus the router's if-id
        // A few others have already been setup at this time
        //  * v6listen is the router's 6bed4 prefix ending in 64 zero bits
        //  * v6listen_linklocal is the address fe80::/128
        //
        lladdr_6bed4 [0] = UDP_PORT_6BED4 & 0xff;
        lladdr_6bed4 [1] = UDP_PORT_6BED4 >> 8;
        memcpy (lladdr_6bed4 + 2, (uint8_t *) &v4name.sin_addr, 4);
        memcpy (&v6listen_complete, &v6listen, 8);
        addr_6bed4(&v6listen_complete, lladdr_6bed4 + 2, ntohs(v4name.sin_port), 0);

        memcpy (v6listen_linklocal_complete, v6listen_linklocal, 8);
        memcpy (v6listen_linklocal_complete + 8, &v6listen_complete.s6_addr [8], 8);
printf ("LISTEN lladdr_6bed4 = %02x:%02x:%02x:%02x:%02x:%02x\n", lladdr_6bed4 [0], lladdr_6bed4 [1], lladdr_6bed4 [2], lladdr_6bed4 [3], lladdr_6bed4 [4], lladdr_6bed4 [5]);
printf ("LISTEN v6listen = %x:%x:%x:%x:%x:%x:%x:%x\n", htons (v6listen.s6_addr16 [0]), htons (v6listen.s6_addr16 [1]), htons (v6listen.s6_addr16 [2]), htons (v6listen.s6_addr16 [3]), htons (v6listen.s6_addr16 [4]), htons (v6listen.s6_addr16 [5]), htons (v6listen.s6_addr16 [6]), htons (v6listen.s6_addr16 [7]));
printf ("LISTEN v6listen_complete = %x:%x:%x:%x:%x:%x:%x:%x\n", htons (v6listen_complete.s6_addr16 [0]), htons (v6listen_complete.s6_addr16 [1]), htons (v6listen_complete.s6_addr16 [2]), htons (v6listen_complete.s6_addr16 [3]), htons (v6listen_complete.s6_addr16 [4]), htons (v6listen_complete.s6_addr16 [5]), htons (v6listen_complete.s6_addr16 [6]), htons (v6listen_complete.s6_addr16 [7]));
printf ("LISTEN v6listen_linklocal = %x:%x:%x:%x:%x:%x:%x:%x\n", htons (((uint16_t *) v6listen_linklocal) [0]), htons (((uint16_t *) v6listen_linklocal) [1]), htons (((uint16_t *) v6listen_linklocal) [2]), htons (((uint16_t *) v6listen_linklocal) [3]), htons (((uint16_t *) v6listen_linklocal) [4]), htons (((uint16_t *) v6listen_linklocal) [5]), htons (((uint16_t *) v6listen_linklocal) [6]), htons (((uint16_t *) v6listen_linklocal) [7]));
printf ("LISTEN v6listen_linklocal_complete = %x:%x:%x:%x:%x:%x:%x:%x\n", htons (((uint16_t *) v6listen_linklocal_complete) [0]), htons (((uint16_t *) v6listen_linklocal_complete) [1]), htons (((uint16_t *) v6listen_linklocal_complete) [2]), htons (((uint16_t *) v6listen_linklocal_complete) [3]), htons (((uint16_t *) v6listen_linklocal_complete) [4]), htons (((uint16_t *) v6listen_linklocal_complete) [5]), htons (((uint16_t *) v6listen_linklocal_complete) [6]), htons (((uint16_t *) v6listen_linklocal_complete) [7]));
        //
        // Start the main daemon process
#ifdef SKIP_TESTING_KLUDGE_IN_FOREGROUND
        switch (fork ()) {
        case -1:                /* Error forking */
                fprintf (stderr, "%s: Failed to fork: %s\n", program, strerror (errno));
                exit (1);
        case 0:                 /* Child process */
                close (0);
                //TODO: tmp.support for ^printf// close (1);
                close (2);
                setsid ();
                run_daemon ();
                break;
        default:                /* Parent process */
                close (v4sox);
                close (v6sox);
                break;
        }
#else
        run_daemon ();
#endif
        //
        // Report successful creation of the daemon
        return 0;
}