http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/mirrors-rsync.html says that rsync://ftp.nl.FreeBSD.org/ has its FreeBSD mirror at vol/3/freebsd-core, but visiting ftp://ftp.nl.freebsd.org/vol/4/freebsd-core/ clearly shows that they've moved it to vol/4/freebsd-core.