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

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Date:	Thu, 8 Oct 2009 17:08:40 +0800
From:	thomas yang <lampsu@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: IP header identification field is zero, why?

> ping sends "echo request" datagrams with DF set (Dont Fragment),
> and ID=0, this is a user program building a packet from scratch.
>
> When linux replies with a "echo reply", DF is not set and an ID is included
> in the answer, increasing at each packet.
>
> About your UDP tests, DF is automatically set, and
> I believe ID on DF frames is generated only for connected sockets.
>

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)
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