I got this hiccup as a result of a build of today's sup.
$ host bc
bc.ai.mit.edu CNAME beet-chex.ai.mit.edu
beet-chex.ai.mit.edu A 128.52.32.22
$ ping bc
ping: Cannot resolve host `bc' (Unknown host)
[Exit 1 ]
$
Looks like the IPv6 changes are nailing me...