Missing first few multicast messages in udp.

Hi,

I am writing a client server code in C. In code the client send the UDP messages to the multicast group. The server(which have joined the group ) receive the packet and process it.

The problem I am facing is that when I run the program ( in the beging of the day) it losses 1 or 2 or 3 first messages and then and works properly there after. And if I run the program again then it works fine (no message even 1st message is not lost).
what would be the problem and also this doesn't t happen very often makes it hard to diagnose.


I have started the server and waited few minutes to update routing table but still it didn't help :(


The servers are on different machines and I am facing this problem only in one server that means the problem is system specific.

I am using linux.


Any help or suggestion would be appreciated.

You're saying the identical server is ran on several machines but the problem appears on only one machine, so this is a configuration or timing issue, right?, is the server really ready when first packets are sent (group joined, etc)? you should also check the first packets are actually received on the machine with tcpdump or any equivalent started before the server. Also notice joining a multicast group is a per-interface property, if several processes have joined the same group, if one of them leave the group, others are still in; so when you try to restart the server (and check you receive everything), there maybe a side effect depending on what is running on the machine (as you may already belong to the mcast group).

nice. I totally forgot about the tcp dump tracing. Will give it a try keeping my fingers crossed.

Thanks a lot root4

tcpdump or wireshark which is a bit more user-friendly