Both the IP-Filter and DP packages come as source code, so you will need a C compiler. Unfortunately, Solaris is missing a C compiler, so:
I have a free C compiler, the GNU C compiler (gcc), supplied by the magnificent Free Software Foundation.[9] You can get the latest version of the compiler from a number of FTP sites.[10] The version that I have used is 2.8.1.
Since the source code for gcc is compressed and tarred, you will also need to get a copy of gzip, the GNU compression utility. Gzip is also available in source form, with the latest version I have used being 1.2.4. It's also worth noting that WinZip can handle tarred, gzipped files.
Sun have still taken the compilers out of Solaris 2.x, so you're still stuck. However, there are pre-compiled packages for Solaris 2.x gcc available in some of the FTP archives. These binaries are usually behind the source versions, so it makes sense to use these binaries to compile the latest source code so that you have the latest version of the compiler. The Solaris Freeware pages contain source code and packages for a lot of free software for Solaris 2.5, 2.6 and 7.[20]
You will also need a copy of make. The GNU version of make experiences some difficulty with the Makefiles supplied by both IP-Filter and DP. However, the Sun-supplied /usr/ccs/bin/make has no problem with either package. Make sure that you have /usr/ccs/bin in your PATH environment variable before wherever you have GNU make installed.