Obtain the INN source distribution from ftp.isc.org in directory /isc/inn/snapshots. The files in the snapshots directory are snapshots of the current inn source taken daily. They are stored in date format; in other words, 0400 5 May 1998 GMT's file is named inn-1998-05-17_04-00.tar.gz. Choose the newest file. The distribution is in gzip compressed tar archive format. To extract it, execute:
gunzip -c <inn-src-file> | tar -xf -
Extracting the source distribution will create a directory named inn where the source resides.