ipv6 packet with routing header type 0, last segment

[Mike Cross <mikec () digitalsushi com>]

One sentence summary: Why does wireshark generate the icmpv6 checksum based
on the routing header type 0 addresses if there are 0 segments remaining,
since the destination address of the ipv6 header field should be used
instead?

I know that type 0 routing headers are depcrecated.  I am just debugging
packets someone else generates.

RFC 2460 says down in 8.1

"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."

Here's my sample capture

http://digitalsushi.com/rh0.seg0_vs_seg1.pcap

In the first packet, I have an ICMPv6 packet with a routing header type 0
that has a segment left.  Wireshark calculates the checksum based on the
destination address in the routing header.  Wireshark even overrides the
destination IP column value with the rh0 address. All of this is as I expect
it to be.

In the second packet, though, there are 0 segments remaining.  Wireshark
again uses the last address in the routing header as the destination, but
this I do not expect.  The packet has already visited this segment, and I
expect the ICMPv6 checksum to be generated on the destination in the IPv6
header, not the routing header.

Per the above specification quote, "at the recipient(s), that address will
be in the Destination Address field of the IPv6 header."  Since this packet
has 0 segments remaining, surely it must be a receipient and should use the
destination address of the IPv6 header.  But wireshark seems to still be
using the last address in the routing header, a segment which has already
been visited.



--mike

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