We have an internal mirror of packages.ros.org that we are using to
build ISOs.
To keep configurations from breaking we need to have packages.ros.org
resolve locally to our internal mirror,
however if our mirror is out of sync we would like to pass through the
request to the real packages.ros.org.

Is there an alternate name for packages.ros.org? us.packages.ros.org?

Is it worth considering listing external mirrors in dns?
eu.packages.ros.org, asia.packages.ros.org, etc