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Document a major IGMP related annoyance.

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Add comments about IGMP bits which will go when we take SSM.
Xref multicast(4).

MFC after:	3 days
This commit is contained in:
Bruce M Simpson 2007-03-18 15:31:06 +00:00
parent c47456c322
commit 04bcf5a9be
1 changed files with 19 additions and 5 deletions
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24
share/man/man4/ip.4
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@ -32,7 +32,7 @@
.\" @(#)ip.4 8.2 (Berkeley) 11/30/93
.\" $FreeBSD$
.\"
.Dd May 14, 2006
.Dd March 18, 2007
.Dt IP 4
.Os
.Sh NAME
@ -199,6 +199,7 @@ control message from
.Xr recvmsg 2
can be used directly as a control message for
.Xr sendmsg 2 .
.\"
.Pp
If the
.Dv IP_ONESBCAST
@ -262,6 +263,7 @@ cmsg_len = sizeof(u_char)
cmsg_level = IPPROTO_IP
cmsg_type = IP_RECVTTL
.Ed
.\"
.Pp
If the
.Dv IP_RECVIF
@ -480,6 +482,8 @@ or the
.Tn IP
address of a particular multicast-capable interface if
the host is multihomed.
.\" TODO: Remove this piece when the RFC 3678 API is implemented and
.\" the RFC 1724 hack is removed.
Since
.Fx 4.4 ,
if the
@ -488,13 +492,22 @@ member is within the network range
.Li 0.0.0.0/8 ,
it is treated as an interface index in the system interface MIB,
as per the RIP Version 2 MIB Extension (RFC-1724).
.\" TODO: Update this piece when IPv4 source-address selection is implemented.
.Pp
Membership is associated with a single interface;
programs running on multihomed hosts may need to
join the same group on more than one interface.
Up to
.Dv IP_MAX_MEMBERSHIPS
memberships may be added on a single socket.
Membership is associated with a single interface;
programs running on multihomed hosts may need to
join the same group on more than one interface.
.Pp
The IGMP protocol uses the primary IP address of the interface
as its identifier for group membership.
If multiple IP aliases are configured on the same interface,
they will be ignored.
This shortcoming was addressed in IPv6; MLDv2 requires
that the unique link-local address for an interface is
used to identify an MLDv2 listener.
.Pp
To drop a membership, use:
.Bd -literal
@ -652,7 +665,8 @@ field was not equal to the length of the datagram written to the socket.
.Xr byteorder 3 ,
.Xr icmp 4 ,
.Xr inet 4 ,
.Xr intro 4
.Xr intro 4 ,
.Xr multicast 4
.Sh HISTORY
The
.Nm