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NAME    [Toc]    [Back]

     multicast -- Multicast Routing

SYNOPSIS    [Toc]    [Back]

     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);

DESCRIPTION    [Toc]    [Back]

     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 protocol.
  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 developer'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    [Toc]    [Back]
     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.  Therefore,
 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 interface
 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,
     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
     ``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 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 physical interface index of the corresponding local

     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
     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 structure
 of ``struct ip6_hdr'' with the next header field ``ip6_nxt'' set to

     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 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    [Toc]    [Back]
     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 compatibility
 is a sort of negotiation between the user-level process and the kernel:

     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 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 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 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 features
 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 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 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
     encapsulation is performed inside the kernel).  If it is set for the special
 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 PIMSM
 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 setsockopt(MRT_API_CONFIG).

     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 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 originated
 locally from the same hosts that performs the encapsulation; otherwise
 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 PIMSM
 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 monitoring.

     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_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) respectively
	 (with the appropriate ``struct bw_upcall'' argument of course).

     From application point of view, a developer needs to know about the following:

      * 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
     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 generated
 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

     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 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) mechanism
 (see the Programming Guide section) .

     Note that the upcalls for a filter are delivered until the specific filter
 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 upcall.

SEE ALSO    [Toc]    [Back]

     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    [Toc]    [Back]

     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 multicast
 code.  The advanced multicast API and the multicast bandwidth monitoring
 were implemented by Pavlin Radoslavov (ICSI) in collaboration
     with Chris Brown (NextHop).

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

FreeBSD 5.2.1		       September 4, 2003		 FreeBSD 5.2.1
[ Back ]
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