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 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);
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;
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 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 = 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));
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
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));
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 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));
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 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.
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 options 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 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
getsockopt
()/
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:
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 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 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_UPCALL
flag.
- 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 */
#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
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;
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 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¶
altq(4),
dummynet(4),
getsockopt(2),
gif(4),
gre(4),
recvfrom(2),
recvmsg(2),
setsockopt(2),
socket(2),
sourcefilter(3),
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 with
PIM-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).