I recommend that all DNS servers be in-bailiwick servers with glue. This recommendation is taken from Dan Bernstein, see https://cr.yp.to/djbdns/notes.html htt

I recommend that all DNS servers be in-bailiwick servers with glue. This recommendation is taken from Dan Bernstein, see https://cr.yp.to/djbdns/notes.html https://cr.yp.to/djbdns/notes.html, section "Gluelessness" It not only improves reliability but can help reduce the number of queries and speed things up.