Wireshark-dev: [Wireshark-dev] Incorrect checksum calculation for UDP packet with ipv6 extensio

From: "Hupfer, Michael" <Michael.Hupfer@xxxxxxxxxx>
Date: Thu, 8 Jul 2021 18:56:45 +0000

Please see packet 4 of the atached capture

 

In my opinion checksum 0xc343 is actually correct, since it is calculated using the final destination address 4ea1:2222:2222::11, but wireshark reports 0x2e12 as correct, which is the result of the checksum calculation if the address from the extension header 505:505:505:505:505:505:505:505 is used.

 

Please refer to RFC 2460:

 

        If the IPv6 packet contains a Routing header, the Destination

         Address used in the pseudo-header is that of the final

         destination.  At the originating node, that address will be in

         the last element of the Routing header; at the recipient(s),

         that address will be in the Destination Address field of the

         IPv6 header.

 

In addition, the Linux kernel accepts the UDP packet.

 

3.4.6 (v3.4.6-0-g6357ac1405b8)

 

Compiled (64-bit) with Qt 5.15.2, with libpcap, with GLib 2.52.3, with zlib

1.2.11, with SMI 0.4.8, with c-ares 1.15.0, with Lua 5.2.4, with GnuTLS 3.6.3

and PKCS #11 support, with Gcrypt 1.8.3, with MIT Kerberos, with MaxMind DB

resolver, with nghttp2 1.39.2, with brotli, with LZ4, with Zstandard, with

Snappy, with libxml2 2.9.9, with QtMultimedia, with automatic updates using

WinSparkle 0.5.7, with AirPcap, with SpeexDSP (using bundled resampler), with

Minizip.

 

Running on 64-bit Windows 10 (2009), build 19043, with Intel(R) Core(TM)

i7-8665U CPU @ 1.90GHz (with SSE4.2), with 32483 MB of physical memory, with

locale German_Germany.utf8, with light display mode, without HiDPI, with Npcap

version 1.31, based on libpcap version 1.10.1-PRE-GIT, with GnuTLS 3.6.3, with

Gcrypt 1.8.3, with brotli 1.0.2, without AirPcap, binary plugins supported (21

loaded).

 

Built using Microsoft Visual Studio 2019 (VC++ 14.28, build 29910).

Attachment: Client_UDP_ExtHead_2021-05-25.pcapng
Description: Client_UDP_ExtHead_2021-05-25.pcapng