Source IP Address of Multicast Join Packets

Hi,


I'm running Linux 2.4.20 on a PC that has one ethernet device.
However, I have it configured as multihomed as follows:


eth0: 192.168.5.100
eth0:1 192.170.1.200


I'm trying to write a multicast program that joins the 239.0.1.1 group
using the second interface (eth0:1). However, when I used ethereal to
snoop on the IGMP join packets, the source IP address of those join
packets is that of eth0 and not eth0:1. I have searched all over the
net and everything states that I should set the imr_interface field of
the mreq structure to the IP address of eth0:1 when I perform the
IP_ADD_MEMBERSHIP setsockopt operation. This doesn't work; it always
uses the IP address of eth0 instead of eth0:1 in the IGMP join packets.

Here's part of my code:


#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h> /* close */


#define SERVER_PORT 5500
#define MAX_MSG 100


int main(int argc, char *argv[]) {


int sd, rc, n, cliLen;
struct ip_mreq mreq;
struct sockaddr_in cliAddr, servAddr;
struct in_addr mcastAddr;
struct hostent *h;
char msg[MAX_MSG];


if(argc!=2) {
printf("usage : %s <mcast address>\n",argv[0]);
exit(0);
}


/* get mcast address to listen to */
h=gethostbyname(argv[1]);
if(h==NULL) {
printf("%s : unknown group '%s'\n",argv[0],argv[1]);
exit(1);
}


memcpy(&mcastAddr, h->h_addr_list[0],h->h_length);


/* check given address is multicast */
if(!IN_MULTICAST(ntohl(mcastAddr.s_addr))) {
printf("%s : given address '%s' is not multicast\n",argv[0],
inet_ntoa(mcastAddr));
exit(1);
}


/* create socket */
sd = socket(AF_INET,SOCK_DGRAM,0);
if(sd<0) {
printf("%s : cannot create socket\n",argv[0]);
exit(1);
}


/* bind port */
servAddr.sin_family=AF_INET;
servAddr.sin_addr.s_addr=htonl(INADDR_ANY);
servAddr.sin_port=htons(SERVER_PORT);
if(bind(sd,(struct sockaddr *) &servAddr, sizeof(servAddr))<0) {
printf("%s : cannot bind port %d \n",argv[0],SERVER_PORT);
exit(1);
}


/* join multicast group */
mreq.imr_multiaddr.s_addr=mcastAddr.s_addr;
mreq.imr_interface.s_addr=inet_addr("192.170.1.200 ");


rc = setsockopt(sd,IPPROTO_IP,IP_ADD_MEMBERSHIP,
(void *) &mreq, sizeof(mreq));
if(rc<0) {
printf("%s : cannot join multicast group '%s'",argv[0],
inet_ntoa(mcastAddr));
exit(1);
}
else {
printf("%s : listening to mgroup %s:%d\n",
argv[0],inet_ntoa(mcastAddr), SERVER_PORT);

(E-Mail Removed) wrote:
> Hi,
>
>
> I'm running Linux 2.4.20 on a PC that has one ethernet device.
> However, I have it configured as multihomed as follows:
>
>
> eth0: 192.168.5.100
> eth0:1 192.170.1.200
>
>
> I'm trying to write a multicast program that joins the 239.0.1.1 group
> using the second interface (eth0:1). However, when I used ethereal to
> snoop on the IGMP join packets, the source IP address of those join
> packets is that of eth0 and not eth0:1. I have searched all over the
> net and everything states that I should set the imr_interface field of
> the mreq structure to the IP address of eth0:1 when I perform the
> IP_ADD_MEMBERSHIP setsockopt operation. This doesn't work; it always
> uses the IP address of eth0 instead of eth0:1 in the IGMP join packets.
>
>

i think is correct so.
Try to look the source code of smcroute or mrouted .
Rembeber the multicast traffic is in Level 2 of ISO/OSI Stack.
bye
peppep

servAddr.sin_addr.s_addr=htonl(INADDR_ANY);
------->>>> Try changing the addr: do not use INADDR_ANY, use
inet_addr("192.170.1.200")

--
jimxu
*NO PAINS, NO GAINS*
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> Hi,
>
>
> I'm running Linux 2.4.20 on a PC that has one ethernet device.
> However, I have it configured as multihomed as follows:
>
>
> eth0: 192.168.5.100
> eth0:1 192.170.1.200
>
>
> I'm trying to write a multicast program that joins the 239.0.1.1 group
> using the second interface (eth0:1). However, when I used ethereal to
> snoop on the IGMP join packets, the source IP address of those join
> packets is that of eth0 and not eth0:1. I have searched all over the
> net and everything states that I should set the imr_interface field of
> the mreq structure to the IP address of eth0:1 when I perform the
> IP_ADD_MEMBERSHIP setsockopt operation. This doesn't work; it always
> uses the IP address of eth0 instead of eth0:1 in the IGMP join packets.
>
> Here's part of my code:
>
>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
> #include <arpa/inet.h>
> #include <netdb.h>
> #include <stdio.h>
> #include <unistd.h> /* close */
>
>
> #define SERVER_PORT 5500
> #define MAX_MSG 100
>
>
> int main(int argc, char *argv[]) {
>
>
> int sd, rc, n, cliLen;
> struct ip_mreq mreq;
> struct sockaddr_in cliAddr, servAddr;
> struct in_addr mcastAddr;
> struct hostent *h;
> char msg[MAX_MSG];
>
>
> if(argc!=2) {
> printf("usage : %s <mcast address>\n",argv[0]);
> exit(0);
> }
>
>
> /* get mcast address to listen to */
> h=gethostbyname(argv[1]);
> if(h==NULL) {
> printf("%s : unknown group '%s'\n",argv[0],argv[1]);
> exit(1);
> }
>
>
> memcpy(&mcastAddr, h->h_addr_list[0],h->h_length);
>
>
> /* check given address is multicast */
> if(!IN_MULTICAST(ntohl(mcastAddr.s_addr))) {
> printf("%s : given address '%s' is not multicast\n",argv[0],
> inet_ntoa(mcastAddr));
> exit(1);
> }
>
>
> /* create socket */
> sd = socket(AF_INET,SOCK_DGRAM,0);
> if(sd<0) {
> printf("%s : cannot create socket\n",argv[0]);
> exit(1);
> }
>
>
> /* bind port */
> servAddr.sin_family=AF_INET;
> servAddr.sin_addr.s_addr=htonl(INADDR_ANY);
> servAddr.sin_port=htons(SERVER_PORT);
> if(bind(sd,(struct sockaddr *) &servAddr, sizeof(servAddr))<0) {
> printf("%s : cannot bind port %d \n",argv[0],SERVER_PORT);
> exit(1);
> }
>
>
> /* join multicast group */
> mreq.imr_multiaddr.s_addr=mcastAddr.s_addr;
> mreq.imr_interface.s_addr=inet_addr("192.170.1.200 ");
>
>
> rc = setsockopt(sd,IPPROTO_IP,IP_ADD_MEMBERSHIP,
> (void *) &mreq, sizeof(mreq));
> if(rc<0) {
> printf("%s : cannot join multicast group '%s'",argv[0],
> inet_ntoa(mcastAddr));
> exit(1);
> }
> else {
> printf("%s : listening to mgroup %s:%d\n",
> argv[0],inet_ntoa(mcastAddr), SERVER_PORT);
>

(E-Mail Removed) wrote:
> Hi,
>
>
> I'm running Linux 2.4.20 on a PC that has one ethernet device.
> However, I have it configured as multihomed as follows:
>
>
> eth0: 192.168.5.100
> eth0:1 192.170.1.200
^^^
Please note that the second address is in a block
managed by Hewlett-Packard. You're working for HP?

--

Tauno Voipio
tauno voipio (at) iki fi

Thanks for your response. Unfortunately, it still doesn't work.
Sending multicast traffic through eth0:1 (192.170.1.200) isn't an
issue; when I monitor the transmitting multicast traffic using
ethereal, the source address is correct - that is, it's set to
192.170.1.200 (eth0:1).

However, to clearify again, the question or problem I'm having is
related to an "IGMP" packet to do the membership join at the beginning,

not a multicast data packet. In that "IGMP" packet, the source address

is eth0 and not eth0:1 (based on what I see from ethereal); I need it
to be eth0:1 for what I'm doing to work. The reason why I need the
source address to be eth0:1 is that the router to which the "IGMP"
packet is sent only has routes for the 192.170.1.x subnet. Hence, I
need the source address in that IGMP join packet to be 192.170.1.200
(eth0:1). Since the source address is that of eth0, the router is
rejecting the IGMP packet as a result of a "non-adjacent" subnet.
Thus, I won't be able to receive multicast traffic from the router.


I have tried the IP_MULTICAST_IF option already but that only relates
to "transmitting multicast traffic"; it won't set the source address of

an "IGMP" join packet correctly. Trust me, I have read the unix
programming manual on multicast and tried a few feasible options but I
just can't get it to work. I actually traced through the multicast
source code in the 2.4.28 linux kernel tree and actually found out that

it uses INADDR_ANY even when you set mreq.imr_interface.s_addr to
192.170.1.200. Hence, it seems like a bug in the code. I have even
sent an email to the main author (Alan Cox) of the multicast task for
linux for help but he hasn't responded yet.