DNS#getIPs silently returns the local host IP for bogus interface names. In this case let's throw an UnknownHostException. This is technically an incompatbile change. I suspect the current behavior was origininally introduced so the interface name "default" works w/o explicitly checking for it. It may also be used in cases where someone is using a shared config file and an option like "dfs.datanode.dns.interface" or "hbase.master.dns.interface" and eg interface "eth3" that some hosts don't have, though I think silently ignorning this is the wrong behavior (those hosts should be configured to use a different interface).