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

The short answer is that you correlate the SEQ# from one side of the
connection with the ACK# you see on the other side of the connection. If
you are seeing SEQ# from after the lost data and the other host is
acknowledging receipt past the lost data, it is highly unlikely that you
will ever see the lost data come across the wire.

Paul




From:
Jonathon <thejunkjon@xxxxxxxxx>
To:
focus-ids@xxxxxxxxxxxxxxxxx
Date:
07/16/2009 12:58 PM
Subject:
Making my own IDS... how to detect packet loss ?



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

-----------------------------------------------------------------
Securing Your Online Data Transfer with SSL.
A guide to understanding SSL certificates, how they operate and their
application. By making use of an SSL certificate on your web server, you
can securely collect sensitive information online, and increase business
by giving your customers confidence that their transactions are safe.
http://www.dinclinx.com/Redirect.aspx?36;5001;25;1371;0;1;946;9a80e04e1a17f194







-----------------------------------------------------------------
Securing Your Online Data Transfer with SSL.
A guide to understanding SSL certificates, how they operate and their application. By making use of an SSL certificate on your web server, you can securely collect sensitive information online, and increase business by giving your customers confidence that their transactions are safe.
http://www.dinclinx.com/Redirect.aspx?36;5001;25;1371;0;1;946;9a80e04e1a17f194

Relevant Pages

  • bug with some em nics on RELENG_7
    ... On two Intel chipset Supermicro boards using the onboard em nics, I seem to have run into an issue where if I boot the box up with the cables unplugged, I cannot get the NICS to properly work post boot up. ... packets transmitted, 0 packets received, 100.0% packet loss ... seq 0, length 64 ...
    (freebsd-stable)
  • Re: Network Performance Issues.
    ... youtube->me http continuation seq 189688 next seq 191136 ... me->youtube tcp ack seq no 192584 ... youtube->me http cont seq 4344 next seq 5792 ... As you can see, in this case, it appears that some packets are being ...
    (Debian-User)
Quantcast