Network tier-2 tests include IPv6-specific tests, unless explicitly filtered-out. When trying to run them on a cluster where IPv6 is not supported, i.e. IPv4 single-stack cluster, then these tests fail on sanity and none of them is executed.
Please make sure to add the `-m not ipv6` filter when executing network tests on clusters that don't support IPv6.
One example is test-pytest-cnv-4.20-post-upgrade-marker-network, which is the most important at this moment due to the upcoming 4.21 GA, but there might be other lanes that are affected by this as well.