Comment 9 for bug 1844712

"Does this mean that the private test networks are only connected externally via the neutron router?"
Yes, that is correct.

The neutron configuration:
https://opendev.org/limestone/ci-cloud-config/src/branch/master/network_bootstrap/bootstrap-neutron.yml

Upstream from the controllers hosting the neutron l3 agents, two static routes exist:
10.4.70.0/24 -> 216.245.200.140
2607:ff68:100:54::/64 -> fd3b:86c4:135e:d033::100

Happy to provide further clarification if needed.