netdev - Re: IP header identification field is zero, why?

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Date:	Thu, 08 Oct 2009 11:18:28 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	thomas yang <lampsu@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: IP header identification field is zero, why?

thomas yang a écrit :

> The IP ID for TCP is non-zero, but for UDP is zero,  strange.
> 
> I want to make the IP ID (not always zero) for UDP packets, what should I do?
> (I want to use 'IP header ID, flags, offset, protocol' to identify an
> IP packets)

As I said, you can connect() your udp socket, if you send/receive trafic to/from a given destination.

if (connected_sock)
	res = connect(sock, (struct sockaddr *)&addr, sizeof(addr));

(Only once)


Then, your sendto() can be faster (because no route lookup is performed)

   if (sendto(sock, buffer, psize, 0,
                  connected_socks ? NULL : (struct sockaddr *)&addr,
                                   sizeof(struct sockaddr_in)) != -1)

Then linux *will* generate an ID for each datagram.
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