Date: Thu, 8 Jun 2000 14:06:27 +0200 (CEST) From: sam@inf.enst.fr To: FreeBSD-gnats-submit@freebsd.org Subject: kern/19121: IPv4 multicast does not work without route Message-ID: <20000608120627.D9AEE1FC@trillian.enst.fr>
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>Number: 19121
>Category: kern
>Synopsis: IPv4 multicast does not work without route
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Thu Jun 08 05:10:03 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator: Samuel Tardieu
>Release: FreeBSD 5.0-CURRENT i386
>Organization:
TELECOM Paris
>Environment:
A FreeBSD box on a private network with IPv4 routes to local
network only. No default route has been set, nor any route for
the 224.0.0.0/8 addresses.
>Description:
When trying to join a multicast group with a
IPPROTO_IP/ADD_MEMBERSHIP ioctl call on a IPv4 socket, FreeBSD
tries to find a suitable network interface using the regular
routing table:
From netinet/ip_output.c:
s = splimp();
/*
* If no interface address was provided, use the interface of
* the route to the given multicast address.
*/
if (mreq.imr_interface.s_addr == INADDR_ANY) {
bzero((caddr_t)&ro, sizeof(ro));
dst = (struct sockaddr_in *)&ro.ro_dst;
dst->sin_len = sizeof(*dst);
dst->sin_family = AF_INET;
dst->sin_addr = mreq.imr_multiaddr;
rtalloc(&ro);
if (ro.ro_rt == NULL) {
error = EADDRNOTAVAIL;
splx(s);
break;
}
ifp = ro.ro_rt->rt_ifp;
rtfree(ro.ro_rt);
}
On a FreeBSD box with one ethernet card connected to a local network
and with no default route, this means that EADDRNOTAVAIL will be
returned when trying to join an IPv4 multicast group.
This is not a theoritical-only case: this happens on a home
network (which sometimes connects to the internet using PPP)
when NTP is launched on the ntp.mcast.net address to reach the
various subnets.
Also, if several interfaces are multicast-capable, at most one of
them will be selected. Packets emitted from the host will be sent
to at most one local network (I believe, I haven't tested this
configuration).
>How-To-Repeat:
Remove your default route, make sure that you have no explicit route
for 224.0.0.0/8 addresses and start sdr. You will get an error
from setsockopt (can't assign requested address).
>Fix:
(I haven't had a chance to test this, it is pure guess)
When no interface is explicitely given, netinet/ip_output.c should
do two things instead of looking for a suitable interface in the
routing table:
(1) Fill a slot in the imo structure with imo_multicast_ifp
field being NULL.
(2) Add a slot for every multicast-capable interface and
subscribe this interface to the multicast group.
Also, when an interface M_MCAST flag is set (or when the interface is
brought up), a new slot should be added. Deletion of a multicast
membership should follow the same logic.
This way, every new interface added to the system (as I do with
my laptop) will automatically start sending multicast packets if
it is multicast capable.
>Release-Note:
>Audit-Trail:
>Unformatted:
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