OPEN-SYSTEM.bear2.Houston1.Level3.net IXFR zone transfer

Changes since SOA version

IXFR is a zone transfer request that returns changes since a specific SOA version. Enter the SOA version to request changes since then.

Not an apex domain The domain OPEN-SYSTEM.bear2.Houston1.Level3.net is not the root of its zone.
Instead, try zone transfer on Houston1.Level3.net .