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MULTICAST(4)	       FreeBSD Kernel Interfaces Manual		  MULTICAST(4)

NAME
     multicast -- Multicast Routing

SYNOPSIS
     options MROUTING

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

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

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

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

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

DESCRIPTION
     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.  The Distance	Vector Multicast Routing Protocol (DVMRP) was the
     first developed multicast routing protocol.  Later, other protocols such
     as	Multicast Extensions to	OSPF (MOSPF), Core Based Trees (CBT), Protocol
     Independent Multicast - Sparse Mode (PIM-SM), and Protocol	Independent
     Multicast - Dense Mode (PIM-DM) were developed as well.

     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
     kernel.

   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;
     ICMP6_FILTER_SETBLOCKALL(&filter);
     setsockopt(mrouter_s6, IPPROTO_ICMPV6, ICMP6_FILTER, (void	*)&filter,
		sizeof(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	= max_rate_limit;
     memcpy(&vc.vifc_lcl_addr, &vif_local_address, sizeof(vc.vifc_lcl_addr));
     if	(vc.vifc_flags & VIFF_TUNNEL)
	 memcpy(&vc.vifc_rmt_addr, &vif_remote_address,
		sizeof(vc.vifc_rmt_addr));
     setsockopt(mrouter_s4, IPPROTO_IP,	MRT_ADD_VIF, (void *)&vc,
		sizeof(vc));

     The ``vif_index'' must be unique per vif.	The ``vif_flags'' contains the
     ``VIFF_*''	flags as defined in <netinet/ip_mroute.h>.  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
     1.	 The ``max_rate_limit''	contains the maximum rate (in bits/s) of the
     multicast data packets forwarded on that vif.  Value of 0 means no	limit.
     The ``vif_local_address'' contains	the local IP address of	the corre-
     sponding 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,
		sizeof(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 physical 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,
		sizeof(vifi));

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

     After the multicast forwarding is enabled,	and the	multicast virtual
     interfaces	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 struc-
     ture 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.  Typi-
     cally, the	upcall would be	a signal for the multicast routing user-level
     process to	install	the appropriate	Multicast Forwarding Cache (MFC) entry
     in	the kernel.

     A 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_s4, 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.

     A 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_s4, 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-
     nel:

     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 doesn't 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
     options and structures are	defined	in <netinet/ip_mroute.h> and
     <netinet6/ip6_mroute.h>, unless stated otherwise.

     The user-level process uses new get/setsockopt() options to perform the
     API features negotiation with the kernel.	This negotiation must be per-
     formed 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 get/setsockopt() options are
     ``MRT_API_SUPPORT'' and ``MRT_API_CONFIG''.  Example:

     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	possi-
     ble 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 get-
     sockopt(MRT_API_SUPPORT) is read-only; in other words, setsock-
     opt(MRT_API_SUPPORT) would	fail.

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

     uint32_t v	= MRT_MFC_FLAGS_DISABLE_WRONGVIF;
     if	(setsockopt(sock, IPPROTO_IP, MRT_API_CONFIG, (void *)&v, sizeof(v))
	 != 0) {
	 return	(ERROR);
     }
     if	(v & MRT_MFC_FLAGS_DISABLE_WRONGVIF)
	 return	(OK);	     /*	Success	*/
     else
	 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, setsock-
     opt(MRT_API_CONFIG) should	be called right	after setsockopt(MRT_INIT).

     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 compatibility reasons they are	added at the end.

     The ``mfcc_flags[MAXVIFS]'' field is used to set various flags per	inter-
     face 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 mul-
     ticast 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 inter-
     faces, 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 Bor-
     der-bit in	PIM Register messages should be	set (in	case when the Register
     encapsulation 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 ker-
     nel-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 setsockopt(MRT_API_CONFIG).

     If	the ``MRT_MFC_RP'' flag	was successfully set by	setsock-
     opt(MRT_API_CONFIG), then the kernel will attempt to perform the PIM Reg-
     ister encapsulation itself	instead	of sending the multicast data packets
     to	user level (inside IGMPMSG_WHOLEPKT upcalls) for user-level encapsula-
     tion.  The	RP address would be taken from the ``mfcc_rp'' field inside
     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
     example 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-
     ing.

     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,
	 because 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_CON-
	 FIG) for the MRT_MFC_BW_UPCALL	flag.

     +o	 The bandwidth-upcall filters are added/deleted	by the new setsock-
	 opt(MRT_ADD_BW_UPCALL)	and setsockopt(MRT_DEL_BW_UPCALL) respectively
	 (with the appropriate ``struct	bw_upcall'' argument of	course).

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

     /*
      *	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 */
     #define BW_UPCALL_THRESHOLD_INTERVAL_MIN_SEC    3
     #define BW_UPCALL_THRESHOLD_INTERVAL_MIN_USEC   0

     The ``bw_upcall'' structure is used as an argument	to setsock-
     opt(MRT_ADD_BW_UPCALL) and	setsockopt(MRT_DEL_BW_UPCALL).	Each setsock-
     opt(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
     PACKETS.  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'', there-
     fore 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;
	     break;
	 }
	 if (is_leq_upcall) {
	     bw_upcall.bu_flags	|= BW_UPCALL_LEQ;
	     break;
	 }
	 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
     message:

     #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 mea-
     sured, 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 forwarded packets.  Hence, this upcall mechanism
     should not	be used	for measuring the exact	value of the bandwidth of the
     forwarded data.  To measure the exact bandwidth, the user would need to
     get the forwarded packets statistics with the ioctl(SIOCGETSGCNT) mecha-
     nism (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 sig-
     nal, but the next upcall will be triggered	no earlier than
     ``bu_threshold.b_time'' after the previous	upcall.

SEE ALSO
     getsockopt(2), recvfrom(2), recvmsg(2), setsockopt(2), socket(2),
     icmp6(4), inet(4),	inet6(4), intro(4), ip(4), ip6(4), pim(4)

AUTHORS
     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 (http://www.kame.net),	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).

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

FreeBSD	10.1		       September 4, 2003		  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | AUTHORS

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