I have attached a packet generator to my platform and am trying to receive UDP packets sent to port 63 and send them back immediately to have a rough idea of my setup's performance. However, my MAC receives the packets fine (as shown in MIB counters). But my recvfrom(..) call never returns. My socket is opened fine and is binded properly to port 63. I see my socket's status in netstat and no error is reported. Is port 63 a special case ? This particular packet generator does not allow me to specify the port to send the packets to and I am stuck with port 63. I appreciate any suggestions you might have here. If you need, I can post my program as well as it is very simple.

Are they sent and recieved from the same host? Are you trying to determine an applications performance or your network performance?

Yes, they are generated by Axia packet generator. The cable is connected to my a port on a switch.
This particular port passes all traffic to another port on the same switch which is connected to my
my MAC inside an FPGA. The generator for my test generates 1000 UDP packet (DA = my MAC address). When
I look at the packet printout, the UDP data says they are being sent to port 63. So my application
binds to my MAC's IP address and port 63. My MAC counters shows 1000 packets received ok. My network
layer statisctis (netdev->stats->rx_count) shows 1000 packets passed to tcp/ip stack fine. However
my recvfrom() sleeps forever...never gets anything.

Just to take a step back, I think I get what you're trying to say but I just want to be sure. Your post might make sense to you but I'm not quite sure if your reference to MAC is your MAC address or your MAC computer.

I havent used an Axia packet generator myself but do you only have the option to set the destination address as a MAC address?

The other thing I'm unclear about is you mentioned that the Axia is connected to a port on your switch and your host is connected to another port on the same switch which might be configured in some kind of monitor mode. So regardless of the destination address you will still get the traffic generated by the Axia.

Seems like you now understood my configuration (on Axia I can set the DA and SA addresses but NOT the UDP
port packets will be sent to). I set the DA to my MAC's DA because I don't want my MAC to drop the packets.
So ..do you have suggestions for me as to why recvfrom() does not return at all ?