There are instances where completely replicating an environment in an air gapped lab is acceptable. For instance, you could be encountering some edge case where

There are instances where completely replicating an environment in an air gapped lab is acceptable. For instance, you could be encountering some edge case where a bit is being flipped in an IP address, or a bit is stuck on somewhere and replicating the environment down to the individual IP addresses plays a huge part in reproducing the issue. An edge router is not one of these cases though.