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More robustly handle asymmetric routes in IPv6 OS detection

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The HLIM feature was miscategorizing probes where the route from the
target was shorter than the route to the target. This would result, e.g.
in a distance calculation of 9 and a received hop limit of 57. Adding
the distance to the hop limit remaining gave a guessed initial hop limit
of 66, which would exceed the "64" category. In IPv4 fingerprints, we
put the TG test (initial TTL guess) as a range of 5 up or down from the
expected number to allow for this and other interference. This patch
does the same for IPv6.
This commit is contained in:
dmiller 2015-05-02 13:25:49 +00:00
parent daf8c58a79
commit e658387ff4
1 changed files with 4 additions and 4 deletions
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8
FPEngine.cc
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@ -800,13 +800,13 @@ static int vectorize_hlim(const PacketElement *pe, int target_distance, enum dis
} else
er_lim = 20;
if (32 - er_lim <= hlim && hlim <= 32)
if (32 - er_lim <= hlim && hlim <= 32+ 5 )
hlim = 32;
else if (64 - er_lim <= hlim && hlim <= 64)
else if (64 - er_lim <= hlim && hlim <= 64+ 5 )
hlim = 64;
else if (128 - er_lim <= hlim && hlim <= 128)
else if (128 - er_lim <= hlim && hlim <= 128+ 5 )
hlim = 128;
else if (255 - er_lim <= hlim && hlim <= 255)
else if (255 - er_lim <= hlim && hlim <= 255+ 5 )
hlim = 255;
else
hlim = -1;