Hi
I find the following socket behavior a bit unexpected. Multicast from
an IPv4 socket (with IP_MULTICAST_IF set) with its source address bound
to INADDR_ANY only works if there is a default route defined, otherwise
send() returns ENETUNREACH.
Default route set, src INADDR_ANY : Works
Default route set, src bind() to interface address : Works
No default route, src INADDR_ANY : Returns ENETUNREACH
No default route, src bind() to interface address : Works
In all cases IP_MULTICAST_IF was set to the outgoing interface and
IP_ADD_MEMBERSHIP was properly called. IGMP membership reports
were seen on the link in all cases.
I believe the cause of this (unless this is the expected behavior?)
is in in_pcbconnect_setup() (netinet/in_pcb.c) [1].
The check for a multicast destination address is run after the attempt
to get the source address by finding a directly connected interface,
this check also returns ENETUNREACH if it fails (which it does for the
destination 224.0.0.0/24 if no default route is set).
Moving the multicast check before the directly connected check solves
this (or any other combinations that makes sure that the
IN_MULTICAST() check is executed).
I've attached a test case and a patch to illustrate it, comments?
Fredrik Lindberg
[1] http://fxr.watson.org/fxr/source/netinet/in_pcb.c#L610
Index: netinet/in_pcb.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/in_pcb.c,v
retrieving revision 1.198
diff -d -u -r1.198 in_pcb.c
--- netinet/in_pcb.c 22 Dec 2007 10:06:11 -0000 1.198
+++ netinet/in_pcb.c 12 Jan 2008 10:48:08 -0000
@@ -618,26 +618,6 @@
if ((inp->inp_socket->so_options & SO_DONTROUTE) == 0)
ia = ip_rtaddr(faddr);
/*
- * If we found a route, use the address corresponding to
- * the outgoing interface.
- *
- * Otherwise assume faddr is reachable on a directly connected
- * network and try to find a corresponding interface to take
- * the source address from.
- */
- if (ia == 0) {
- bzero(&sa, sizeof(sa));
- sa.sin_addr = faddr;
- sa.sin_len = sizeof(sa);
- sa.sin_family = AF_INET;
-
- ia = ifatoia(ifa_ifwithdstaddr(sintosa(&sa)));
- if (ia == 0)
- ia = ifatoia(ifa_ifwithnet(sintosa(&sa)));
- if (ia == 0)
- return (ENETUNREACH);
- }
- /*
* If the destination address is multicast and an outgoing
* interface has been set as a multicast option, use the
* address of that interface as our source address.
@@ -657,6 +637,26 @@
return (EADDRNOTAVAIL);
}
}
+ /*
+ * If we found a route, use the address corresponding to
+ * the outgoing interface.
+ *
+ * Otherwise assume faddr is reachable on a directly connected
+ * network and try to find a corresponding interface to take
+ * the source address from.
+ */
+ if (ia == 0) {
+ bzero(&sa, sizeof(sa));
+ sa.sin_addr = faddr;
+ sa.sin_len = sizeof(sa);
+ sa.sin_family = AF_INET;
+
+ ia = ifatoia(ifa_ifwithdstaddr(sintosa(&sa)));
+ if (ia == 0)
+ ia = ifatoia(ifa_ifwithnet(sintosa(&sa)));
+ if (ia == 0)
+ return (ENETUNREACH);
+ }
laddr = ia->ia_addr.sin_addr;
}
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