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MULTICAST(4)		 BSD Kernel Interfaces Manual		  MULTICAST(4)

     multicast -- Multicast Routing

     options MROUTING

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netinet/in.h>
     #include <netinet/ip_mroute.h>
     #include <netinet6/ip6_mroute.h>

     getsockopt(int s, IPPROTO_IP, MRT_INIT, void *optval, socklen_t *optlen);

     setsockopt(int s, IPPROTO_IP, MRT_INIT, const void	*optval,
	   socklen_t optlen);

     getsockopt(int s, IPPROTO_IPV6, MRT6_INIT,	void *optval,
	   socklen_t *optlen);

     setsockopt(int s, IPPROTO_IPV6, MRT6_INIT,	const void *optval,
	   socklen_t optlen);

     Multicast routing is used to efficiently propagate	data packets to	a set
     of	multicast listeners in multipoint networks.  If	unicast	is used	to
     replicate the data	to all listeners, then some of the network links may
     carry multiple copies of the same data packets.  With multicast routing,
     the overhead is reduced to	one copy (at most) per network link.

     All multicast-capable routers must	run a common multicast routing proto-
     col.  It is recommended that either Protocol Independent Multicast	-
     Sparse Mode (PIM-SM), or Protocol Independent Multicast - Dense Mode
     (PIM-DM) are used,	as these are now the generally accepted	protocols in
     the Internet community.  The HISTORY section discusses previous multicast
     routing protocols.

     To	start multicast	routing, the user must enable multicast	forwarding in
     the kernel	(see SYNOPSIS about the	kernel configuration options), and
     must run a	multicast routing capable user-level process.  From devel-
     oper's point of view, the programming guide described in the Programming
     Guide section should be used to control the multicast forwarding in the

   Programming Guide
     This section provides information about the basic multicast routing API.
     The so-called "advanced multicast API" is described in the	Advanced
     Multicast API Programming Guide section.

     First, a multicast	routing	socket must be open.  That socket would	be
     used to control the multicast forwarding in the kernel.  Note that	most
     operations	below require certain privilege	(i.e., root privilege):

     /*	IPv4 */
     int mrouter_s4;
     mrouter_s4	= socket(AF_INET, SOCK_RAW, IPPROTO_IGMP);

     int mrouter_s6;
     mrouter_s6	= socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

     Note that if the router needs to open an IGMP or ICMPv6 socket (in	case
     of	IPv4 and IPv6 respectively) for	sending	or receiving of	IGMP or	MLD
     multicast group membership	messages, then the same	mrouter_s4 or
     mrouter_s6	sockets	should be used for sending and receiving respectively
     IGMP or MLD messages.  In case of BSD-derived kernel, it may be possible
     to	open separate sockets for IGMP or MLD messages only.  However, some
     other kernels (e.g., Linux) require that the multicast routing socket
     must be used for sending and receiving of IGMP or MLD messages.  There-
     fore, for portability reason the multicast	routing	socket should be
     reused for	IGMP and MLD messages as well.

     After the multicast routing socket	is open, it can	be used	to enable or
     disable multicast forwarding in the kernel:

     /*	IPv4 */
     int v = 1;	       /* 1 to enable, or 0 to disable */
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_INIT, (void	*)&v, sizeof(v));

     /*	IPv6 */
     int v = 1;	       /* 1 to enable, or 0 to disable */
     setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_INIT, (void *)&v, sizeof(v));
     /*	If necessary, filter all ICMPv6	messages */
     struct icmp6_filter filter;
     setsockopt(mrouter_s6, IPPROTO_ICMPV6, ICMP6_FILTER, (void	*)&filter,

     After multicast forwarding	is enabled, the	multicast routing socket can
     be	used to	enable PIM processing in the kernel if we are running PIM-SM
     or	PIM-DM (see pim(4)).

     For each network interface	(e.g., physical	or a virtual tunnel) that
     would be used for multicast forwarding, a corresponding multicast inter-
     face must be added	to the kernel:

     /*	IPv4 */
     struct vifctl vc;
     memset(&vc, 0, sizeof(vc));
     /*	Assign all vifctl fields as appropriate	*/
     vc.vifc_vifi = vif_index;
     vc.vifc_flags = vif_flags;
     vc.vifc_threshold = min_ttl_threshold;
     vc.vifc_rate_limit	= 0;
     memcpy(&vc.vifc_lcl_addr, &vif_local_address, sizeof(vc.vifc_lcl_addr));
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_ADD_VIF, (void *)&vc,

     The vif_index must	be unique per vif.  The	vif_flags contains the VIFF_*
     flags as defined in <netinet/ip_mroute.h>.	 The VIFF_TUNNEL flag is no
     longer supported by FreeBSD.  Users who wish to forward multicast data-
     grams over	a tunnel should	consider configuring a gif(4) or gre(4)	tunnel
     and using it as a physical	interface.

     The min_ttl_threshold contains the	minimum	TTL a multicast	data packet
     must have to be forwarded on that vif.  Typically,	it would have value of

     The max_rate_limit	argument is no longer supported	in FreeBSD and should
     be	set to 0.  Users who wish to rate-limit	multicast datagrams should
     consider the use of dummynet(4) or	altq(4).

     The vif_local_address contains the	local IP address of the	corresponding
     local interface.  The vif_remote_address contains the remote IP address
     in	case of	DVMRP multicast	tunnels.

     /*	IPv6 */
     struct mif6ctl mc;
     memset(&mc, 0, sizeof(mc));
     /*	Assign all mif6ctl fields as appropriate */
     mc.mif6c_mifi = mif_index;
     mc.mif6c_flags = mif_flags;
     mc.mif6c_pifi = pif_index;
     setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_ADD_MIF,	(void *)&mc,

     The mif_index must	be unique per vif.  The	mif_flags contains the MIFF_*
     flags as defined in <netinet6/ip6_mroute.h>.  The pif_index is the	physi-
     cal interface index of the	corresponding local interface.

     A multicast interface is deleted by:

     /*	IPv4 */
     vifi_t vifi = vif_index;
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_DEL_VIF, (void *)&vifi,

     /*	IPv6 */
     mifi_t mifi = mif_index;
     setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_DEL_MIF,	(void *)&mifi,

     After the multicast forwarding is enabled,	and the	multicast virtual in-
     terfaces are added, the kernel may	deliver	upcall messages	(also called
     signals later in this text) on the	multicast routing socket that was open
     earlier with MRT_INIT or MRT6_INIT.  The IPv4 upcalls have	struct igmpmsg
     header (see <netinet/ip_mroute.h>)	with field im_mbz set to zero.	Note
     that this header follows the structure of struct ip with the protocol
     field ip_p	set to zero.  The IPv6 upcalls have struct mrt6msg header (see
     <netinet6/ip6_mroute.h>) with field im6_mbz set to	zero.  Note that this
     header follows the	structure of struct ip6_hdr with the next header field
     ip6_nxt set to zero.

     The upcall	header contains	field im_msgtype and im6_msgtype with the type
     of	the upcall IGMPMSG_* and MRT6MSG_* for IPv4 and	IPv6 respectively.
     The values	of the rest of the upcall header fields	and the	body of	the
     upcall message depend on the particular upcall type.

     If	the upcall message type	is IGMPMSG_NOCACHE or MRT6MSG_NOCACHE, this is
     an	indication that	a multicast packet has reached the multicast router,
     but the router has	no forwarding state for	that packet.  Typically, the
     upcall would be a signal for the multicast	routing	user-level process to
     install the appropriate Multicast Forwarding Cache	(MFC) entry in the

     An	MFC entry is added by:

     /*	IPv4 */
     struct mfcctl mc;
     memset(&mc, 0, sizeof(mc));
     memcpy(&mc.mfcc_origin, &source_addr, sizeof(mc.mfcc_origin));
     memcpy(&mc.mfcc_mcastgrp, &group_addr, sizeof(mc.mfcc_mcastgrp));
     mc.mfcc_parent = iif_index;
     for (i = 0; i < maxvifs; i++)
	 mc.mfcc_ttls[i] = oifs_ttl[i];
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_ADD_MFC,
		(void *)&mc, sizeof(mc));

     /*	IPv6 */
     struct mf6cctl mc;
     memset(&mc, 0, sizeof(mc));
     memcpy(&mc.mf6cc_origin, &source_addr, sizeof(mc.mf6cc_origin));
     memcpy(&mc.mf6cc_mcastgrp,	&group_addr, sizeof(mf6cc_mcastgrp));
     mc.mf6cc_parent = iif_index;
     for (i = 0; i < maxvifs; i++)
	 if (oifs_ttl[i] > 0)
	     IF_SET(i, &mc.mf6cc_ifset);
     setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_ADD_MFC,
		(void *)&mc, sizeof(mc));

     The source_addr and group_addr are	the source and group address of	the
     multicast packet (as set in the upcall message).  The iif_index is	the
     virtual interface index of	the multicast interface	the multicast packets
     for this specific source and group	address	should be received on.	The
     oifs_ttl[]	array contains the minimum TTL (per interface) a multicast
     packet should have	to be forwarded	on an outgoing interface.  If the TTL
     value is zero, the	corresponding interface	is not included	in the set of
     outgoing interfaces.  Note	that in	case of	IPv6 only the set of outgoing
     interfaces	can be specified.

     An	MFC entry is deleted by:

     /*	IPv4 */
     struct mfcctl mc;
     memset(&mc, 0, sizeof(mc));
     memcpy(&mc.mfcc_origin, &source_addr, sizeof(mc.mfcc_origin));
     memcpy(&mc.mfcc_mcastgrp, &group_addr, sizeof(mc.mfcc_mcastgrp));
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_DEL_MFC,
		(void *)&mc, sizeof(mc));

     /*	IPv6 */
     struct mf6cctl mc;
     memset(&mc, 0, sizeof(mc));
     memcpy(&mc.mf6cc_origin, &source_addr, sizeof(mc.mf6cc_origin));
     memcpy(&mc.mf6cc_mcastgrp,	&group_addr, sizeof(mf6cc_mcastgrp));
     setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_DEL_MFC,
		(void *)&mc, sizeof(mc));

     The following method can be used to get various statistics	per installed
     MFC entry in the kernel (e.g., the	number of forwarded packets per	source
     and group address):

     /*	IPv4 */
     struct sioc_sg_req	sgreq;
     memset(&sgreq, 0, sizeof(sgreq));
     memcpy(&sgreq.src,	&source_addr, sizeof(sgreq.src));
     memcpy(&sgreq.grp,	&group_addr, sizeof(sgreq.grp));
     ioctl(mrouter_s4, SIOCGETSGCNT, &sgreq);

     /*	IPv6 */
     struct sioc_sg_req6 sgreq;
     memset(&sgreq, 0, sizeof(sgreq));
     memcpy(&sgreq.src,	&source_addr, sizeof(sgreq.src));
     memcpy(&sgreq.grp,	&group_addr, sizeof(sgreq.grp));
     ioctl(mrouter_s6, SIOCGETSGCNT_IN6, &sgreq);

     The following method can be used to get various statistics	per multicast
     virtual interface in the kernel (e.g., the	number of forwarded packets
     per interface):

     /*	IPv4 */
     struct sioc_vif_req vreq;
     memset(&vreq, 0, sizeof(vreq));
     vreq.vifi = vif_index;
     ioctl(mrouter_s4, SIOCGETVIFCNT, &vreq);

     /*	IPv6 */
     struct sioc_mif_req6 mreq;
     memset(&mreq, 0, sizeof(mreq));
     mreq.mifi = vif_index;
     ioctl(mrouter_s6, SIOCGETMIFCNT_IN6, &mreq);

   Advanced Multicast API Programming Guide
     If	we want	to add new features in the kernel, it becomes difficult	to
     preserve backward compatibility (binary and API), and at the same time to
     allow user-level processes	to take	advantage of the new features (if the
     kernel supports them).

     One of the	mechanisms that	allows us to preserve the backward compatibil-
     ity is a sort of negotiation between the user-level process and the ker-

     1.	  The user-level process tries to enable in the	kernel the set of new
	  features (and	the corresponding API) it would	like to	use.

     2.	  The kernel returns the (sub)set of features it knows about and is
	  willing to be	enabled.

     3.	  The user-level process uses only that	set of features	the kernel has
	  agreed on.

     To	support	backward compatibility,	if the user-level process does not ask
     for any new features, the kernel defaults to the basic multicast API (see
     the Programming Guide section).  Currently, the advanced multicast	API
     exists only for IPv4; in the future there will be IPv6 support as well.

     Below is a	summary	of the expandable API solution.	 Note that all new op-
     tions and structures are defined in <netinet/ip_mroute.h> and
     <netinet6/ip6_mroute.h>, unless stated otherwise.

     The user-level process uses new getsockopt()/setsockopt() options to per-
     form the API features negotiation with the	kernel.	 This negotiation must
     be	performed right	after the multicast routing socket is open.  The set
     of	desired/allowed	features is stored in a	bitset (currently, in
     uint32_t; i.e., maximum of	32 new features).  The new
     getsockopt()/setsockopt() options are MRT_API_SUPPORT and MRT_API_CONFIG.

     uint32_t v;
     getsockopt(sock, IPPROTO_IP, MRT_API_SUPPORT, (void *)&v, sizeof(v));

     would set in v the	pre-defined bits that the kernel API supports.	The
     eight least significant bits in uint32_t are same as the eight possible
     flags MRT_MFC_FLAGS_* that	can be used in mfcc_flags as part of the new
     definition	of struct mfcctl (see below about those	flags),	which leaves
     24	flags for other	new features.  The value returned by
     getsockopt(MRT_API_SUPPORT) is read-only; in other	words,
     setsockopt(MRT_API_SUPPORT) would fail.

     To	modify the API,	and to set some	specific feature in the	kernel,	then:

     if	(setsockopt(sock, IPPROTO_IP, MRT_API_CONFIG, (void *)&v, sizeof(v))
	 != 0) {
	 return	(ERROR);
	 return	(OK);	     /*	Success	*/
	 return	(ERROR);

     In	other words, when setsockopt(MRT_API_CONFIG) is	called,	the argument
     to	it specifies the desired set of	features to be enabled in the API and
     the kernel.  The return value in v	is the actual (sub)set of features
     that were enabled in the kernel.  To obtain later the same	set of fea-
     tures that	were enabled, then:

     getsockopt(sock, IPPROTO_IP, MRT_API_CONFIG, (void	*)&v, sizeof(v));

     The set of	enabled	features is global.  In	other words,
     setsockopt(MRT_API_CONFIG)	should be called right after

     Currently,	the following set of new features is defined:

     #define MRT_MFC_FLAGS_DISABLE_WRONGVIF (1 << 0) /*	disable	WRONGVIF signals */
     #define MRT_MFC_FLAGS_BORDER_VIF	(1 << 1)  /* border vif		     */
     #define MRT_MFC_RP			(1 << 8)  /* enable RP address	     */
     #define MRT_MFC_BW_UPCALL		(1 << 9)  /* enable bw upcalls	     */

     The advanced multicast API	uses a newly defined struct mfcctl2 instead of
     the traditional struct mfcctl.  The original struct mfcctl	is kept	as is.
     The new struct mfcctl2 is:

      *	The new	argument structure for MRT_ADD_MFC and MRT_DEL_MFC overlays
      *	and extends the	old struct mfcctl.
     struct mfcctl2 {
	     /*	the mfcctl fields */
	     struct in_addr  mfcc_origin;	/* ip origin of	mcasts	     */
	     struct in_addr  mfcc_mcastgrp;	/* multicast group associated*/
	     vifi_t	     mfcc_parent;	/* incoming vif		     */
	     u_char	     mfcc_ttls[MAXVIFS];/* forwarding ttls on vifs   */

	     /*	extension fields */
	     uint8_t	     mfcc_flags[MAXVIFS];/* the	MRT_MFC_FLAGS_*	flags*/
	     struct in_addr  mfcc_rp;		 /* the	RP address	     */

     The new fields are	mfcc_flags[MAXVIFS] and	mfcc_rp.  Note that for	com-
     patibility	reasons	they are added at the end.

     The mfcc_flags[MAXVIFS] field is used to set various flags	per interface
     per (S,G) entry.  Currently, the defined flags are:

     #define MRT_MFC_FLAGS_DISABLE_WRONGVIF (1 << 0) /*	disable	WRONGVIF signals */
     #define MRT_MFC_FLAGS_BORDER_VIF	    (1 << 1) /*	border vif	    */

     The MRT_MFC_FLAGS_DISABLE_WRONGVIF	flag is	used to	explicitly disable the
     IGMPMSG_WRONGVIF kernel signal at the (S,G) granularity if	a multicast
     data packet arrives on the	wrong interface.  Usually, this	signal is used
     to	complete the shortest-path switch in case of PIM-SM multicast routing,
     or	to trigger a PIM assert	message.  However, it should not be delivered
     for interfaces that are not in the	outgoing interface set,	and that are
     not expecting to become an	incoming interface.  Hence, if the
     MRT_MFC_FLAGS_DISABLE_WRONGVIF flag is set	for some of the	interfaces,
     then a data packet	that arrives on	that interface for that	MFC entry will
     NOT trigger a WRONGVIF signal.  If	that flag is not set, then a signal is
     triggered (the default action).

     The MRT_MFC_FLAGS_BORDER_VIF flag is used to specify whether the Border-
     bit in PIM	Register messages should be set	(in case when the Register en-
     capsulation is performed inside the kernel).  If it is set	for the	spe-
     cial PIM Register kernel virtual interface	(see pim(4)), the Border-bit
     in	the Register messages sent to the RP will be set.

     The remaining six bits are	reserved for future usage.

     The mfcc_rp field is used to specify the RP address (in case of PIM-SM
     multicast routing)	for a multicast	group G	if we want to perform kernel-
     level PIM Register	encapsulation.	The mfcc_rp field is used only if the
     MRT_MFC_RP	advanced API flag/capability has been successfully set by

     If	the MRT_MFC_RP flag was	successfully set by
     setsockopt(MRT_API_CONFIG), then the kernel will attempt to perform the
     PIM Register encapsulation	itself instead of sending the multicast	data
     packets to	user level (inside IGMPMSG_WHOLEPKT upcalls) for user-level
     encapsulation.  The RP address would be taken from	the mfcc_rp field in-
     side the new struct mfcctl2.  However, even if the	MRT_MFC_RP flag	was
     successfully set, if the mfcc_rp field was	set to INADDR_ANY, then	the
     kernel will still deliver an IGMPMSG_WHOLEPKT upcall with the multicast
     data packet to the	user-level process.

     In	addition, if the multicast data	packet is too large to fit within a
     single IP packet after the	PIM Register encapsulation (e.g., if its size
     was on the	order of 65500 bytes), the data	packet will be fragmented, and
     then each of the fragments	will be	encapsulated separately.  Note that
     typically a multicast data	packet can be that large only if it was	origi-
     nated locally from	the same hosts that performs the encapsulation;	other-
     wise the transmission of the multicast data packet	over Ethernet for ex-
     ample would have fragmented it into much smaller pieces.

     Typically,	a multicast routing user-level process would need to know the
     forwarding	bandwidth for some data	flow.  For example, the	multicast
     routing process may want to timeout idle MFC entries, or in case of PIM-
     SM	it can initiate	(S,G) shortest-path switch if the bandwidth rate is
     above a threshold for example.

     The original solution for measuring the bandwidth of a dataflow was that
     a user-level process would	periodically query the kernel about the	number
     of	forwarded packets/bytes	per (S,G), and then based on those numbers it
     would estimate whether a source has been idle, or whether the source's
     transmission bandwidth is above a threshold.  That	solution is far	from
     being scalable, hence the need for	a new mechanism	for bandwidth monitor-

     Below is a	description of the bandwidth monitoring	mechanism.

     o	 If the	bandwidth of a data flow satisfies some	pre-defined filter,
	 the kernel delivers an	upcall on the multicast	routing	socket to the
	 multicast routing process that	has installed that filter.

     o	 The bandwidth-upcall filters are installed per	(S,G).	There can be
	 more than one filter per (S,G).

     o	 Instead of supporting all possible comparison operations (i.e., < <=
	 == != > >= ), there is	support	only for the <=	and >= operations, be-
	 cause this makes the kernel-level implementation simpler, and because
	 practically we	need only those	two.  Further, the missing operations
	 can be	simulated by secondary user-level filtering of those <=	and >=
	 filters.  For example,	to simulate !=,	then we	need to	install	filter
	 "bw <=	0xffffffff", and after an upcall is received, we need to check
	 whether "measured_bw != expected_bw".

     o	 The bandwidth-upcall mechanism	is enabled by
	 setsockopt(MRT_API_CONFIG) for	the MRT_MFC_BW_UPCALL flag.

     o	 The bandwidth-upcall filters are added/deleted	by the new
	 setsockopt(MRT_ADD_BW_UPCALL) and setsockopt(MRT_DEL_BW_UPCALL) re-
	 spectively (with the appropriate struct bw_upcall argument of

     From application point of view, a developer needs to know about the fol-

      *	Structure for installing or delivering an upcall if the
      *	measured bandwidth is above or below a threshold.
      *	User programs (e.g. daemons) may have a	need to	know when the
      *	bandwidth used by some data flow is above or below some	threshold.
      *	This interface allows the userland to specify the threshold (in
      *	bytes and/or packets) and the measurement interval. Flows are
      *	all packet with	the same source	and destination	IP address.
      *	At the moment the code is only used for	multicast destinations
      *	but there is nothing that prevents its use for unicast.
      *	The measurement	interval cannot	be shorter than	some Tmin (currently, 3s).
      *	The threshold is set in	packets	and/or bytes per_interval.
      *	Measurement works as follows:
      *	For >= measurements:
      *	The first packet marks the start of a measurement interval.
      *	During an interval we count packets and	bytes, and when	we
      *	pass the threshold we deliver an upcall	and we are done.
      *	The first packet after the end of the interval resets the
      *	count and restarts the measurement.
      *	For <= measurement:
      *	We start a timer to fire at the	end of the interval, and
      *	then for each incoming packet we count packets and bytes.
      *	When the timer fires, we compare the value with	the threshold,
      *	schedule an upcall if we are below, and	restart	the measurement
      *	(reschedule timer and zero counters).

     struct bw_data {
	     struct timeval  b_time;
	     uint64_t	     b_packets;
	     uint64_t	     b_bytes;

     struct bw_upcall {
	     struct in_addr  bu_src;	     /*	source address		  */
	     struct in_addr  bu_dst;	     /*	destination address	  */
	     uint32_t	     bu_flags;	     /*	misc flags (see	below)	  */
     #define BW_UPCALL_UNIT_PACKETS (1 << 0) /*	threshold (in packets)	  */
     #define BW_UPCALL_UNIT_BYTES   (1 << 1) /*	threshold (in bytes)	  */
     #define BW_UPCALL_GEQ	    (1 << 2) /*	upcall if bw >=	threshold */
     #define BW_UPCALL_LEQ	    (1 << 3) /*	upcall if bw <=	threshold */
     #define BW_UPCALL_DELETE_ALL   (1 << 4) /*	delete all upcalls for s,d*/
	     struct bw_data  bu_threshold;   /*	the bw threshold	  */
	     struct bw_data  bu_measured;    /*	the measured bw		  */

     /*	max. number of upcalls to deliver together */
     #define BW_UPCALLS_MAX			     128
     /*	min. threshold time interval for bandwidth measurement */

     The bw_upcall structure is	used as	an argument to
     setsockopt(MRT_ADD_BW_UPCALL) and setsockopt(MRT_DEL_BW_UPCALL).  Each
     setsockopt(MRT_ADD_BW_UPCALL) installs a filter in	the kernel for the
     source and	destination address in the bw_upcall argument, and that	filter
     will trigger an upcall according to the following pseudo-algorithm:

      if (bw_upcall_oper IS ">=") {
	 if (((bw_upcall_unit &	PACKETS	== PACKETS) &&
	      (measured_packets	>= threshold_packets)) ||
	     ((bw_upcall_unit &	BYTES == BYTES)	&&
	      (measured_bytes >= threshold_bytes)))
	    SEND_UPCALL("measured bandwidth is >= threshold");
       if (bw_upcall_oper IS "<=" && measured_interval >= threshold_interval) {
	 if (((bw_upcall_unit &	PACKETS	== PACKETS) &&
	      (measured_packets	<= threshold_packets)) ||
	     ((bw_upcall_unit &	BYTES == BYTES)	&&
	      (measured_bytes <= threshold_bytes)))
	    SEND_UPCALL("measured bandwidth is <= threshold");

     In	the same bw_upcall the unit can	be specified in	both BYTES and PACK-
     ETS.  However, the	GEQ and	LEQ flags are mutually exclusive.

     Basically,	an upcall is delivered if the measured bandwidth is >= or <=
     the threshold bandwidth (within the specified measurement interval).  For
     practical reasons,	the smallest value for the measurement interval	is 3
     seconds.  If smaller values are allowed, then the bandwidth estimation
     may be less accurate, or the potentially very high	frequency of the gen-
     erated upcalls may	introduce too much overhead.  For the >= operation,
     the answer	may be known before the	end of threshold_interval, therefore
     the upcall	may be delivered earlier.  For the <= operation	however, we
     must wait until the threshold interval has	expired	to know	the answer.

     Example of	usage:

     struct bw_upcall bw_upcall;
     /*	Assign all bw_upcall fields as appropriate */
     memset(&bw_upcall,	0, sizeof(bw_upcall));
     memcpy(&bw_upcall.bu_src, &source,	sizeof(bw_upcall.bu_src));
     memcpy(&bw_upcall.bu_dst, &group, sizeof(bw_upcall.bu_dst));
     bw_upcall.bu_threshold.b_data = threshold_interval;
     bw_upcall.bu_threshold.b_packets =	threshold_packets;
     bw_upcall.bu_threshold.b_bytes = threshold_bytes;
     if	(is_threshold_in_packets)
	 bw_upcall.bu_flags |= BW_UPCALL_UNIT_PACKETS;
     if	(is_threshold_in_bytes)
	 bw_upcall.bu_flags |= BW_UPCALL_UNIT_BYTES;
     do	{
	 if (is_geq_upcall) {
	     bw_upcall.bu_flags	|= BW_UPCALL_GEQ;
	 if (is_leq_upcall) {
	     bw_upcall.bu_flags	|= BW_UPCALL_LEQ;
	 return	(ERROR);
     } while (0);
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_ADD_BW_UPCALL,
	       (void *)&bw_upcall, sizeof(bw_upcall));

     To	delete a single	filter,	then use MRT_DEL_BW_UPCALL, and	the fields of
     bw_upcall must be set exactly same	as when	MRT_ADD_BW_UPCALL was called.

     To	delete all bandwidth filters for a given (S,G),	then only the bu_src
     and bu_dst	fields in struct bw_upcall need	to be set, and then just set
     only the BW_UPCALL_DELETE_ALL flag	inside field bw_upcall.bu_flags.

     The bandwidth upcalls are received	by aggregating them in the new upcall

     #define IGMPMSG_BW_UPCALL	4  /* BW monitoring upcall */

     This message is an	array of struct	bw_upcall elements (up to
     BW_UPCALLS_MAX = 128).  The upcalls are delivered when there are 128
     pending upcalls, or when 1	second has expired since the previous upcall
     (whichever	comes first).  In an struct upcall element, the	bu_measured
     field is filled-in	to indicate the	particular measured values.  However,
     because of	the way	the particular intervals are measured, the user	should
     be	careful	how bu_measured.b_time is used.	 For example, if the filter is
     installed to trigger an upcall if the number of packets is	>= 1, then
     bu_measured may have a value of zero in the upcalls after the first one,
     because the measured interval for >= filters is "clocked" by the for-
     warded packets.  Hence, this upcall mechanism should not be used for mea-
     suring the	exact value of the bandwidth of	the forwarded data.  To	mea-
     sure the exact bandwidth, the user	would need to get the forwarded	pack-
     ets statistics with the ioctl(SIOCGETSGCNT) mechanism (see	the
     Programming Guide section)	.

     Note that the upcalls for a filter	are delivered until the	specific fil-
     ter is deleted, but no more frequently than once per bu_threshold.b_time.
     For example, if the filter	is specified to	deliver	a signal if bw >= 1
     packet, the first packet will trigger a signal, but the next upcall will
     be	triggered no earlier than bu_threshold.b_time after the	previous up-

     getsockopt(2), recvfrom(2), recvmsg(2), setsockopt(2), socket(2),
     sourcefilter(3), altq(4), dummynet(4), gif(4), gre(4), icmp6(4), igmp(4),
     inet(4), inet6(4),	intro(4), ip(4), ip6(4), mld(4), pim(4)

     The Distance Vector Multicast Routing Protocol (DVMRP) was	the first de-
     veloped multicast routing protocol.  Later, other protocols such as Mul-
     ticast Extensions to OSPF (MOSPF) and Core	Based Trees (CBT), were	devel-
     oped as well.  Routers at autonomous system boundaries may	now exchange
     multicast routes with peers via the Border	Gateway	Protocol (BGP).	 Many
     other routing protocols are able to redistribute multicast	routes for use
     with PIM-SM and PIM-DM.

     The original multicast code was written by	David Waitzman (BBN Labs), and
     later modified by the following individuals: Steve	Deering	(Stanford),
     Mark J. Steiglitz (Stanford), Van Jacobson	(LBL), Ajit Thyagarajan
     (PARC), Bill Fenner (PARC).  The IPv6 multicast support was implemented
     by	the KAME project (,	and was	based on the IPv4 mul-
     ticast code.  The advanced	multicast API and the multicast	bandwidth mon-
     itoring were implemented by Pavlin	Radoslavov (ICSI) in collaboration
     with Chris	Brown (NextHop).  The IGMPv3 and MLDv2 multicast support was
     implemented by Bruce Simpson.

     This manual page was written by Pavlin Radoslavov (ICSI).

BSD				 May 27, 2009				   BSD


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