On Thu, 20 Apr 2006, Andrew Athan wrote:
>
> 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");
> }
> }
12:54:07.780277 IP 206.200.5.144.2232 > 224.0.17.44.55300: UDP, length 136
^^^___ datagram
Question? Don't you need to use:
socklen_t slen = sizeof(localSock);
recvfrom(sd, databuf, datalen, &localSock, &slen);
... to receive a datagram?
Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.89 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
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