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IPv6 Plugin for Snort

This Snort Plugin contains a preprocessor to monitor IPv6 neighbor discovery messages and adds new rule options for IPv6 specific signatures.

For more information see


The Plugin builds with automake and autoconf, but the setup is quite primitive.

It also requires the Snort sources for some header files (obtain them e.g. with apt-get source snort) and it currently uses pkg-config to retrieve Snort config options, i.e. it needs an installed Snort package.

I use these commands to fetch the Snort source code and compile this plugin (on Debian):

(cd /tmp; apt-get source snort)
./configure --prefix=/usr CFLAGS="-I/tmp/snort-"
make install

To test the correct compilation activate the preprocessor (see below) and check if it is loaded.

If the configuration flags do not match the configuration flags of your Snort installation then the plugin loading should abort with an error like this:

ERROR size 856 != 792
ERROR: Failed to initialize dynamic preprocessor: IPv6 Preprocessor version 1.3.0 (-2)


Enable Preprocessor

There are two steps to use a plugin:

  1. Snort has to load the shared library. Either copy the library into the directory configured with dynamicpreprocessor directory /some/path, or selectively load the library file with dynamicpreprocessor file /some/path/
  2. The preprocessor has to be enabled by adding the configuration line preprocessor ipv6

Now the IPv6 preprocessor should be listed among the other loaded preprocessors when starting Snort, and it should print its own summary when exiting Snort.

Add Preprocessor Rules

Newer Snort versions use decoder and preprocessor rules by default. So in order to use the plugin one has to add its preprocessor rules to Snort's configuration files. etc/preprocessor.rules and etc/ contain basic metadata on the plugin's events and should be appended to the system's preprocessor.rules and files.

Configure Preprocessor

The preprocessor ipv6 line in snort.conf takes several optional parameters to provide further information about the network.

Two useful parameters are the router_mac and the net_prefix. If these are set then the preprocessor can perform additional checks and raise an alert if it sees a rogue router or wrong network prefixes on-link.


preprocessor ipv6: \
  router_mac 00:00:0C:01:02:03 00:00:0C:01:02:04 \
  net_prefix 2001:db8:1:2::/64

Add Signatures

The file etc/ipv6.rules contain some experimental rules for IPv6 network operation. These can be tested by including the file in snort.conf, but they should be read first because they need some customization (e.g. the DHCPv6 rules should be disabled in a DHCPv6-managed network).


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