NAME
multicast — Multicast RoutingSYNOPSIS
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 protocol. 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 developer'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);
/* 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));
/* 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,
sizeof(vc));
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
datagrams 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 1.
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,
sizeof(mc));
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));
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 kernel.
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));
/* 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));
/* 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);
/* 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 compatibility is a sort of negotiation between the user-level process and the kernel:- The user-level process tries to enable in the kernel the set of new features (and the corresponding API) it would like to use.
- The kernel returns the (sub)set of features it knows about and is willing to be enabled.
- The user-level process uses only that set of features the kernel has agreed on.
MRT_API_SUPPORT and
MRT_API_CONFIG. Example:
uint32_t v; getsockopt(sock, IPPROTO_IP, MRT_API_SUPPORT, (void *)&v, sizeof(v));
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:
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);
getsockopt(sock, IPPROTO_IP, MRT_API_CONFIG, (void *)&v, sizeof(v));
#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 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 */
};
#define MRT_MFC_FLAGS_DISABLE_WRONGVIF (1 << 0) /* disable WRONGVIF signals */ #define MRT_MFC_FLAGS_BORDER_VIF (1 << 1) /* border vif */
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 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
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 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 monitoring.
Below is a description of the bandwidth monitoring mechanism.
- 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.
- The bandwidth-upcall filters are installed per (S,G). There can be more than one filter per (S,G).
- 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”.
- The bandwidth-upcall mechanism is enabled by
setsockopt(MRT_API_CONFIG)
for the
MRT_MFC_BW_UPCALLflag. - 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).
/*
* 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
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");
}
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));
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 */
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
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)HISTORY
The Distance Vector Multicast Routing Protocol (DVMRP) was the first developed multicast routing protocol. Later, other protocols such as Multicast Extensions to OSPF (MOSPF) and Core Based Trees (CBT), were developed 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 withPIM-SM and
PIM-DM.
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 multicast code. The advanced multicast API and the multicast bandwidth monitoring 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).| May 27, 2009 | Debian |