Function X_ip_mforward

freebsd/netinet/ip_mroute.c:1221–1431

#define TUNNEL_LEN  12  /* # bytes of IP option for tunnel encapsulation  */

static int
X_ip_mforward(struct ip *ip, struct ifnet *ifp, struct mbuf *m,
    struct ip_moptions *imo)
{
    struct mfc *rt;
    int error;
    vifi_t vifi;

    CTR3(KTR_IPMF, "ip_mforward: delete mfc orig 0x%08x group %lx ifp %p",
	ntohl(ip->ip_src.s_addr), (u_long)ntohl(ip->ip_dst.s_addr), ifp);

    if (ip->ip_hl < (sizeof(struct ip) + TUNNEL_LEN) >> 2 ||
		((u_char *)(ip + 1))[1] != IPOPT_LSRR ) {
	/*
	 * Packet arrived via a physical interface or
	 * an encapsulated tunnel or a register_vif.
	 */
    } else {
	/*
	 * Packet arrived through a source-route tunnel.
	 * Source-route tunnels are no longer supported.
	 */
	return (1);
    }

    VIF_LOCK();
    MFC_LOCK();
    if (imo && ((vifi = imo->imo_multicast_vif) < V_numvifs)) {
	if (ip->ip_ttl < MAXTTL)
	    ip->ip_ttl++;	/* compensate for -1 in *_send routines */
	error = ip_mdq(m, ifp, NULL, vifi);
	MFC_UNLOCK();
	VIF_UNLOCK();
	return error;
    }

    /*
     * Don't forward a packet with time-to-live of zero or one,
     * or a packet destined to a local-only group.
     */
    if (ip->ip_ttl <= 1 || IN_LOCAL_GROUP(ntohl(ip->ip_dst.s_addr))) {
	MFC_UNLOCK();
	VIF_UNLOCK();
	return 0;
    }

    /*
     * Determine forwarding vifs from the forwarding cache table
     */
    MRTSTAT_INC(mrts_mfc_lookups);
    rt = mfc_find(&ip->ip_src, &ip->ip_dst);

    /* Entry exists, so forward if necessary */
    if (rt != NULL) {
	error = ip_mdq(m, ifp, rt, -1);
	MFC_UNLOCK();
	VIF_UNLOCK();
	return error;