Multicast recvfrom not working??????

I'm trying to setup a multicast client that listens in on eth1 witht
the address: 172.16.90.11
the address on which the stream is coming in is: 239.7.7.1
the socket is setup fine without any problems but i still don't get any
data....in the recvfrom call
i've gone through almost every reference i've found...but still can't
figure out whats going on...can anyone help...
below is the code that I'm using to set it up:

//all the used variables are defined in the header file (no compile
issues here):
//running it on a debian box enabled for multicast

memset(&mcast_addr, 0, sizeof(mcast_addr));
mcast_addr.sin_family = AF_INET;
mcast_addr.sin_port = htons(mPort);
mcast_addr.sin_addr.s_addr = inet_addr("239.7.7.1");

memset(&cli_addr, 0, sizeof(cli_addr));
cli_addr.sin_family = AF_INET;
cli_addr.sin_port = htons(mPort);
cli_addr.sin_addr.s_addr = inet_addr("172.16.90.11");

if((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP))< 0)
exit(-1);

int iSize = 65535;
if(setsockopt(sock, SOL_SOCKET, SO_RCVBUF, (const char*)&iSize,
sizeof(iSize)) < 0)
exit(-1);


int bTrue = 1;
if(setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &bTrue, sizeof(bTrue))
< 0){
exit(-1);

int ret;
if ((ret = bind(sock, (struct sockaddr*)&cli_addr, sizeof(cli_addr))
)< 0)
exit(-1);


//unsigned long Addr = cli_addr.sin_addr.s_addr;
struct in_addr interface_addr;
if(inet_aton("172.16.90.11", &(interface_addr) ) != 1)
cout << "the addr thing failed" << endl;

if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF,
(char*)&interface_addr, sizeof(interface_addr)) < 0)
exit(-1);


if(inet_aton(mAddress.c_str() , &(mreq.imr_multiaddr) ) != 1)
cout << "imr_multiaddr failed" << endl;
if(inet_aton("172.16.90.11", &(mreq.imr_interface)) != 1)
cout << "imr_interface failed" << endl;


if(setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&mreq,
sizeof(mreq)) < 0)
exit(-1);

int iTTL =0;
if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&iTTL,
sizeof(iTTL)) < 0)
exit(-1);


if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_LOOP, (char*)&bFalse,
sizeof(bFalse)) < 0)
exit(-1);



while(true){
int iFromLen = sizeof(from);
if(recvfrom(sock, mBuffer, MAX_SIZE, 0, &from,
(socklen_t*)&iFromLen) > 0){
cout << "got a message" << endl;
}
}

(E-Mail Removed) wrote:

> I'm trying to setup a multicast client that listens in on eth1 witht
> the address: 172.16.90.11
> the address on which the stream is coming in is: 239.7.7.1

While 239.7.7.1 is a multicast address, it is not in the recommended range of
234.0.0.0 to 238.255.255.255

> memset(&mcast_addr, 0, sizeof(mcast_addr));
> mcast_addr.sin_family = AF_INET;
> mcast_addr.sin_port = htons(mPort);
> mcast_addr.sin_addr.s_addr = inet_addr("239.7.7.1");
>
> memset(&cli_addr, 0, sizeof(cli_addr));
> cli_addr.sin_family = AF_INET;
> cli_addr.sin_port = htons(mPort);
> cli_addr.sin_addr.s_addr = inet_addr("172.16.90.11");

It is usually a good idea to use INADDR_ANY.

<snip>
> int bTrue = 1;
> if(setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &bTrue, sizeof(bTrue))
> < 0){
> exit(-1);

I assume you are using the SO_REUSEADDR socket option because the client and
server are on the same computer?

<snip>
> if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF,
> (char*)&interface_addr, sizeof(interface_addr)) < 0)
> exit(-1);

Generally you never need to set the IP_MULTICAST_IF option unless you have a
multihomed computer.

<snip>
> int iTTL =0;
> if(setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (char*)&iTTL,
> sizeof(iTTL)) < 0)
> exit(-1);

Why are you setting the TTL to 0? I believe it needs to be 1 even for loopback
on the same computer.

--
Phil Frisbie, Jr.
Hawk Software
http://www.hawksoft.com

thanks Phil

> While 239.7.7.1 is a multicast address, it is not in the recommended range of
> 234.0.0.0 to 238.255.255.255

the address 239.7.7.1 is what the servers uses, unfortunately I can't
do much about it.

> It is usually a good idea to use INADDR_ANY.

I am notusing INADDR_ANY since I'm certain that eth1 is connected
receives the multicast packets, but should that cause any problems?

> I assume you are using the SO_REUSEADDR socket option because the client and
> server are on the same computer?

No. The client and the server are running on two different machines. My
client is on the same LAN. If i don't use that option, bind fails for
some reason.

> Generally you never need to set the IP_MULTICAST_IF option unless you have a
> multihomed computer.

Could you please explain what you mean by a multihomed computer?

> Why are you setting the TTL to 0? I believe it needs to be 1 even for loopback
> on the same computer.

I don't plan to send out messages, so I don't expect setting TTL to 0
causing any problems

I'm going to try all that you have suggested, and see if it works.
Besides the above, do you have any other clues as to why i'm not
getting anything in the recvfrom call?

(E-Mail Removed) wrote:

>>It is usually a good idea to use INADDR_ANY.
>
> I am notusing INADDR_ANY since I'm certain that eth1 is connected
> receives the multicast packets, but should that cause any problems?

It makes your software more fragile, and one more thing the user must set up in
a config file. Just use INADDR_ANY and let the OS use the proper address.

>>I assume you are using the SO_REUSEADDR socket option because the client and
>>server are on the same computer?
>
> No. The client and the server are running on two different machines. My
> client is on the same LAN. If i don't use that option, bind fails for
> some reason.

If bind() fails then there is already another application bound to that port.
You need to find out what that is and either shut it down or use another port.

>>Generally you never need to set the IP_MULTICAST_IF option unless you have a
>>multihomed computer.
>
> Could you please explain what you mean by a multihomed computer?

Multihomed means you have two or more network cards attached to different networks.

>>Why are you setting the TTL to 0? I believe it needs to be 1 even for loopback
>>on the same computer.
>
> I don't plan to send out messages, so I don't expect setting TTL to 0
> causing any problems

Then just leave it at the default which is 1.

> I'm going to try all that you have suggested, and see if it works.
> Besides the above, do you have any other clues as to why i'm not
> getting anything in the recvfrom call?

I suspect the bind() problem could be the cause, but keep us posted.

--
Phil Frisbie, Jr.
Hawk Software
http://www.hawksoft.com