IDS: Making my own IDS... how to detect packet loss ?

[Jonathon <thejunkjon () gmail com>]

I am writing my own IDS.  I have a packet sniffer + TCP reassembler
that I've written.  For each stream I detect, I have to keep some
state + a buffer of the packets for the stream.  However, a problem
that I've run into is that sometimes packets could get lost (meaning I
do not capture them, but they were actually sent/received between two
hosts on the network).  If I do drop the packets, my current
implementation gets all messed up since I never end up freeing the
resources I've allocated for that stream.  So, lost packets seem to be
the bain of my current implementation.

My question is (assuming all TCP streams), how can I determine whether
a packet is lost by just looking at packets that I currently have in
my buffer?

The packets could come in any order so just because I receive a packet
with seq #N, doesn't mean that a packet with seq #N-1 was sent.

I hope this is the appropriate mailing list for my question.

Thanks
J

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