netdev - Re: What causes these TCP packet getting lost in linux kernel

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Message-ID: <CAJzFV34Z077yQv71X8WSQ2U-6iCNPnsPDBNaSFoQabxHG_q-2w@mail.gmail.com>
Date:	Mon, 14 Apr 2014 11:58:21 -0600
From:	Sharat Masetty <sharat04@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	chptx y <chptxy@...il.com>, David Newall <davidn@...idnewall.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: What causes these TCP packet getting lost in linux kernel

Thats a good find.. Is this drop count documented in netstat stats?

Thanks
Sharat

On Mon, Apr 14, 2014 at 8:13 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2014-04-14 at 17:20 +0800, chptx y wrote:
>> i don't know why, no matter I capture packets on my Ubuntu PC or
>> Android device with tcpdump,  open the output file with wireshark, all
>> output packets are marked with "incorrect checksum", but it seems that
>> this problem don't affect  subsequent packets interaction. why?
>
> Checksums are filled by the NIC on TX packets, some tcpdump/wireshark
> versions do not really know of this.
>
> packet 30 (which is accepted) has TSval=4054079470 & TSecr=22894,
> but packet 32 has TSval=4054078149 & TSecr=22863, while its sequence is
> correct (coming after the prior packet)
>
> Sender has a wrong implementation of TCP Timestamps (RFC 1323), or a
> middlebox mangles timestamps badly.
>
> Receiver considers this as an old packet.
>
>
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