The https://www.freebsd.org/doc/handbook/eresources.html page links to the planet.freebsdish.org, however this domain doesn't resolve. Moreover, we now have https://planet.freebsd.org/
A commit references this bug: Author: bcr Date: Mon Aug 15 15:21:40 UTC 2016 New revision: 49283 URL: https://svnweb.freebsd.org/changeset/doc/49283 Log: Remove dead link to planet.freebsdish.org and replace it with one that works. PR: 211704 Submitted by: knezour@weboutsourcing.cz Sponsored by: BSDCam DevSummit Changes: head/en_US.ISO8859-1/books/handbook/eresources/chapter.xml
I've replaced the link. Thanks for reporting the issue and suggesting the solution. PR closed.