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

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Date:	Mon, 14 Apr 2014 07:13:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	chptx y <chptxy@...il.com>
Cc:	David Newall <davidn@...idnewall.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: What causes these TCP packet getting lost in linux kernel

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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