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Winsock2 socket() : does protocol = 0 work for SOCK_DGRAM

Posted on 2009-05-05
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Last Modified: 2013-11-29
After creating a UDP socket, binding it to a particular IP Address & port, subsequent calls to iocltsocket to determine if any data awaiting receipt constantly indicates 0 ...... although network sniffer indicates messages destined for specified IP Address & port have been transmitted by sender.

However, when creating the UDP socket if specify IPPROTO_UDP in protocol parameter of socket call (instead of zero), messages are subsequently received as expected.

Why ?
Any suggestions gratefully received as need to understand.
OptionValue = SO_SYNCHRONOUS_NONALERT
setsockopt (INVALID_SOCKET, SOL_SOCKET, SO_OPENTYPE, &OptionValue, sizeof(optionvalue))
 
udp_socket = socket (AF_INET, SOCK_DGRAM, 0)
bind (udp_socket, (PSOCKADDR)&local_sin, sin_len)
ioctlsocket (udp_socket, FIONBIO, &argp)       // where argp non-zero
 
.....
 
ioctlsocket (udp_socket, FIONREAD, &argp)
if argp==0 then no data received
NO DATA RECEIVED
----------------------------------------------------------------------------------------------------------------
OptionValue = SO_SYNCHRONOUS_NONALERT
setsockopt (INVALID_SOCKET, SOL_SOCKET, SO_OPENTYPE, &OptionValue, sizeof(optionvalue))
 
udp_socket = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP)
bind (udp_socket, (PSOCKADDR)&local_sin, sin_len)
ioctlsocket (udp_socket, FIONBIO, &argp)       // where argp non-zero
 
.....
 
ioctlsocket (udp_socket, FIONREAD, &argp)
if argp==0 then no data received
OCCASIONALLY argp NON-ZERO ie: DATA RECEIVED

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Question by:chas_newport
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4 Comments
 
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Assisted Solution

by:BigRat
BigRat earned 400 total points
ID: 24312859
The last parameter of the socket() call is the protocol parameter. When you set this to zero the system takes the default protocol for the type of socket being created, which is in this case IPPROTO_IP. Therefore to use the UDP protocol you must set the parameter to IPPROTO_UDP.
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Author Comment

by:chas_newport
ID: 24315500
Many thanks for responding BigRat,

I guess I do not understand the difference between the 2 protocols.

I thought that if a server socket was created with protocol of IPPROTO_IP then any socket with a compatible definition could communicate with this socket.
ie: a 'client' socket created with IPPROTO_UDP protocol could communicate with this 'server' socket defined with a 'universal protocol' of IPPROTO_IP.
Is my understanding correct ?

Perhaps in my example, this is only valid when other options are applied to one or both sockets.

Could you please shed some more light.

Many thanks
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LVL 27

Assisted Solution

by:BigRat
BigRat earned 400 total points
ID: 24316125
The IP protocol is a message system based on IP addresses. It can support several "sub-protocols" based on exactly what is sent in the messages and how subsequent messages are handled. This gives you the possibility of defining your own protocol on top of IP.

UDP is a stateless IP protocol, where as TCP/IP is a state-full protocol. The UDP protocol does NOT guarentee message delivery, whereas TCP/IP establishes a stream and does guarentee delivery (but not necessarily in the correct order!) Both "sit" on top of IP.

If you look at the diagram in http://en.wikipedia.org/wiki/TCP/IP showing the layers from Frame upwards, you'll see that each "protocol" adds a header of it's own. Any good book on TCP/IP or networking protocols will give you the messy details you don't need to know. That's the good thing about this layered system, originally defined as the ISO, and developed in the 80's for the Arpanet.
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Accepted Solution

by:
chas_newport earned 0 total points
ID: 24539322
Many thanks for your assistance BigRat,

The issue has finally been resolved ...... and wasn't related to the protocol but a peculiarity with the equipment processing.

Thanks again
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