david d8ce681711 Simplify and document the invalid destination options header. ...

The packet construction had a bug that made it more effective in at
least one case for me. Weilin had supplied a 16-byte destination options
buffer, including some random bytes from a packet capture. But the
length of buffer was set incorrectly in the packet, making it look like
it was 8 bytes instead of 16. Therefore the expected ICMPv6 packet
started in the middle of the buffer, making it appear to have a
type/code of 254/24 instead of 128/0 as expected.

I tried setting the proper length, while keeping the invalid destination
option, but then stopped getting a Parameter Problem response. I also
tried setting a proper destination options buffer with no invalid
options, followed by ICMPv6 with type/code of 128/0, and again got no
response. It appears that I get a response only when both of these
conditions are satisfied: 1) an invalid destination option exists, and
2) the ICMPv6 type is unknown. This is against OS X.

The probe was being effective by accident, but now I've simplified it
and documented these strange conditions.

This breaks any hosts that might have ignored the invalid destination
option (which they shouldn't do) and replied to the echo request. But we
have targets-ipv6-multicast-echo for that.

2011-09-02 04:11:07 +00:00

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