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[lwip-devel] [bug #46467] ip_frag() shouldn't modify pbuf in case of a r

From: Zach Smith
Subject: [lwip-devel] [bug #46467] ip_frag() shouldn't modify pbuf in case of a retransmission
Date: Mon, 17 Oct 2016 23:34:48 +0000 (UTC)
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36

Follow-up Comment #12, bug #46467 (project lwip):

It looks like the reassembled IP fragment is getting rejected because of an
incorrect TCP checksum. I tried another test where I connect to my lwip device
that is doing the fragmenting with another lwip device (instead of a PC). The
ip packets that are not fragmented are sent and received with no error but the
first fragmented packet gets rejected in lwip tcp_input() for failing tcp
checksum. Also, if I enable checksum validation in wireshark I can see that
the TCP checksum is invalid

The wireshark traces I attached 10/13 showed a PC ( connecting
to the lwip device ( but I attached a new one that shows two
lwip devices. This time connects as a TCP client to starts fragmenting packets and with wireshark TCP
checksum validation enabled, you can see that the TCP checksum is invalid for
the fragmented packets.

I'm not sure why at this point. Any ideas?

(file #38749)

Additional Item Attachment:

File name: ip_frag_two_lwip_devices.pcapng Size:138 KB


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