Fine Control of FreeBSD port

MASTER_SITES controls where the port fetches its source from. By setting MASTER_SITE to the site of a known good source code tarball, you can control where the port downloads from. For example, if you use the command make MASTER_SITE=ftp://ftp2.freebsd.org/pub/FreeBSD/distfiles, then fetch will attempt to pull the distfile directly from that site.

If you want to pull the distfile directly from a FreeBSD repository, you can specify MASTER_SITE_FREEBSD=YES. The distfile probably exists there. Most FreeBSD mirrors are already heavily loaded, so please avoid this.

Probably the most useful option for maintainers of large FreeBSD networks is MASTER_SITE_OVERRIDE. The network administrator can build a central repository of important distfiles on a local server. The site listed in MASTER_SITE_OVERRIDE is checked for distfiles before any remote sites are contacted. This saves on exterior bandwidth and makes fetching distfiles more reliable.

For more details go here.