recvfrom failing with error 11

Question

Hi

I am trying out a udpclient program which uses sendto and recvfrom functions. I am setting SO_RCVTIMEO value as 10 seconds for my socket.

I am binding the socket to source ipaddress and sourceport. When I check the netstat I can see that there is no other process which is binded with the same values. My bind operation is also successfull.

Then I am doing a sendto which is sending a echo request to destination. After sendto I am doing a recvfrom. But recvfrom fail's saying ERRNO 11 which means try again :(

But if I check the wireshark logs I can see ECHO REQUEST and ECHO REPLY which is coming within few milliseconds but still recvfrom is not able to read it :(. In wireshark I am seeing the UDP ECHO REQUEST AND UDP ECHO REPLY.

I dont have any FIREWALL enabled in my system.

Is there any way to debug this issue :( I am really doubting the RECV operation is there any way to find out if the packet is being sent to my sockFD or not ???

UPDATE1: My linux PC is connected to another linux pc acting as a server via switch.

Answer 1

EAGAIN from recvfrom() implies one of three things:

• The socket has been set to non-blocking; or
• The MSG_DONTWAIT flag was used; or
• The receive timeout has expired.

It sounds like your socket is non-blocking to me.

Answer 2

I have the found out the ISSUE atlast ...

Seems UDP checksum of the packet is wrong as a result IP STACK is dropping the packet before it reach's SOCKET :( as a result recvfrom is getting timeout and coming out.