"u32" match support

modulename: xt_u32.ko


Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>Core Netfilter Configuration
└─>"u32" match support
In linux kernel since version 2.6.23 (release Date: 2007-10-09)  
u32 allows you to extract quantities of up to 4 bytes from a packet,
AND them with specified masks, shift them by specified amounts and
test whether the results are in any of a set of specified ranges.
The specification of what to extract is general enough to skip over
headers with lengths stored in the packet, as in IP or TCP header

Details and examples are in the kernel module source.

source code: