Hi all.  There is an interesting project that was called opendpi 
(originally by ipoque GmbH) and recently been forked and maintained by 
the ntop guys under the nDPI label.  It offers a new and currently 
maintained layer 7 (L7) packet identification library.  It could 
definitely benefit from more eyes and development effort, but at present 
it gives much better breakdown of traffic for ntop

There is a netfilter library, originally by Elian Gidoni, that I have 
updated to use the nDPI fork

https://github.com/ewildgoose/ndpi-netfilter



The practical upshot is that you can do stuff like:

     iptables -I FORWARD -m ndpi --WinUpdate -j LOG
or
     iptables -I FORWARD -m ndpi --skype -j REJECT

In theory you can also filter Facebook, Twitter, etc, as specific named 
protocols - this ability is likely to be improved in the next iterations 
(ie be more configurable)

Another of the clever things that nDPI does is to try and classify SSL 
traffic by examining the name on the cert.  A technique that seems 
likely to allow crude identification of significant traffic. (If the 
cert says "mail.google.com", have a guess what we are doing?)


The big picture here is that a lot of protocols are starting to look 
like "http", and increasingly more are just "https". Any filters are 
going to be reasonably easy for an active attacker to defeat (tunnel it 
some way), but I have a requirement to save users from themselves and so 
we want to be able to do things like limiting Windows Update and 
disallow it over the expensive satellite connection, and only allow over 
the cheaper wifi (or 3G) connections.

Simple filtering on http & https is quite useful in implementing that 
despite the limitations. Forcing connections through squid has some 
limitations (and some advantages), but at present squid can't do some of 
the things we can do with nDPI such as examining SSL certs.

There is still some way to go on this project, but I started pondering 
how I might express such rules in shorewall (and trying to avoid further 
overloading MARKs).

Kind regards

Ed W

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