Unable to receive multicast stream

From: Andrew Athan
Date: Thu Apr 20 2006 - 13:38:04 EST


The simple UDP multicast receive application below, adapted from source on IBM's web site, will not receive any data. While it is blocked on recv():

hfclinux2:/home/root/UDP/apps/Crosser2# netstat -ang
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 224.0.0.1
eth0 1 224.0.0.1
eth1 1 224.0.17.44
eth1 1 224.0.0.1
lo 1 ff02::1
eth0 1 ff02::1:ffdd:eb2b
eth0 1 ff02::1
eth1 1 ff02::1:ffdd:eb2c
eth1 1 ff02::1


And tcpdump shows traffic arriving at the interface(see below)! This leads me to belive the kernel is filtering it, and or not delivering it to the socket.

The one "strange" thing about this network is that the traffic is flowing in "dense mode", meaning there is no explicit need for IGMP messaging (nor any response to such messaging).

Can anyone point me in the right direction regarding why the socket never receives any data????

Thanks.
Andrew

hfclinux2:/home/root/UDP/apps/Crosser2# uname -a
Linux hfclinux2 2.6.15.1smp #6 SMP PREEMPT Mon Feb 13 11:38:32 EST 2006 i686 GNU/Linux

hfclinux2:/home/root/UDP/apps/Crosser2# tcpdump -i eth1 port 55300
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
12:54:06.980000 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 91
12:54:07.079675 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 46
12:54:07.179869 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 181
12:54:07.280437 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 181
12:54:07.380005 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 181
12:54:07.480073 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 136
12:54:07.680459 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 91
12:54:07.780277 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 136


hfclinux2:/home/root/UDP/apps/Crosser2# ifconfig
eth0 Link encap:Ethernet HWaddr 00:11:43:DD:EB:2B
inet addr:172.22.71.128 Bcast:172.22.71.255 Mask:255.255.255.0
inet6 addr: fe80::211:43ff:fedd:eb2b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:19540 errors:0 dropped:0 overruns:0 frame:0
TX packets:7838 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1563190 (1.4 MiB) TX bytes:1943895 (1.8 MiB)
Base address:0xdcc0 Memory:dfae0000-dfb00000

eth0:1 Link encap:Ethernet HWaddr 00:11:43:DD:EB:2B
inet addr:10.61.6.128 Bcast:10.61.6.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Base address:0xdcc0 Memory:dfae0000-dfb00000

eth0:2 Link encap:Ethernet HWaddr 00:11:43:DD:EB:2B
inet addr:196.0.34.11 Bcast:196.0.34.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Base address:0xdcc0 Memory:dfae0000-dfb00000

eth0:3 Link encap:Ethernet HWaddr 00:11:43:DD:EB:2B
inet addr:192.168.254.128 Bcast:192.168.254.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Base address:0xdcc0 Memory:dfae0000-dfb00000

eth1 Link encap:Ethernet HWaddr 00:11:43:DD:EB:2C
inet addr:192.168.250.128 Bcast:192.168.250.255 Mask:255.255.255.0
inet6 addr: fe80::211:43ff:fedd:eb2c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:137717 errors:0 dropped:0 overruns:0 frame:0
TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:58314262 (55.6 MiB) TX bytes:1596 (1.5 KiB)
Base address:0xccc0 Memory:df8e0000-df900000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)



-------------------------
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

using namespace std;


struct sockaddr_in localSock;
struct ip_mreqn group;
int sd;
int datalen;
char databuf[10];

int main (int argc, char *argv[])
{
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (sd < 0) {
perror("opening datagram socket");
exit(1);
}

{
int reuse=1;

if (setsockopt(sd, SOL_SOCKET, SO_REUSEADDR,
(char *)&reuse, sizeof(reuse)) < 0) {
perror("setting SO_REUSEADDR");
close(sd);
exit(1);
}
}

memset((char *) &localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(55300);;
localSock.sin_addr.s_addr = INADDR_ANY;

if (bind(sd, (struct sockaddr*)&localSock, sizeof(localSock))) {
perror("binding datagram socket");
close(sd);
exit(1);
}


group.imr_multiaddr.s_addr = inet_addr("224.0.17.44");
printf("%d\n",group.imr_multiaddr.s_addr);
group.imr_address.s_addr = inet_addr("192.168.250.128");
if (setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP,
(char *)&group, sizeof(group)) < 0) {
perror("adding multicast group");
close(sd);
exit(1);
}
/*
* Read from the socket.
*/
datalen = sizeof(databuf);
if (read(sd, databuf, datalen) < 0) {
perror("reading datagram message");
close(sd);
exit(1);
} else {
puts("success reading");
}
}


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