Date: Sat, 12 Jan 2008 12:06:59 +0100 From: Fredrik Lindberg <fli@shapeshifter.se> To: freebsd-net@freebsd.org Subject: Unexpected multicast IPv4 socket behavior Message-ID: <47889F53.4010605@shapeshifter.se>
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This is a multi-part message in MIME format. --------------010609050507030507010803 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 --------------010609050507030507010803 Content-Type: text/x-patch; name="in_pcb.c-multicast.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="in_pcb.c-multicast.patch" 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; } --------------010609050507030507010803--
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