the no route to host message means one of two things, either there is no actual route, which would have generated a different error, or some firewall is sending back a new route message.
I have seen the now route to host problem several times, and it is usually because there is a firewall in place that no one is expecting to be there. In the following IP and PORT are the IP address and port from the failure message in your log file. the server machine is the machine that has IP as an address, and the remote machine is the machine that the connection is failing on. The way to diagnose this explicitly is: 1) on the server machine that should be accepting connections on the port, telnet localhost PORT, and telnet IP PORT you should get a connection, if not then the server is not binding the port. 2) on the remote machine verify that you can communicate to the server machine via normal tools such as ssh and or ping and or traceroute, using the IP address from the error message in your log file 3) on the remote machine run telnet IP PORT. if (1) and (2) succeeded and (3) does not, then there is something blocking packets for the port range in question. If (3) does succeed then there is some probably interesting problem. On Wed, Apr 22, 2009 at 7:31 AM, Stas Oskin <stas.os...@gmail.com> wrote: > Hi. > > "No route to host" generally means machines have routing problems. Machine > A > > doesnt know how to route packets to Machine B. Reboot everything, router > > first, see if it goes away. Otherwise, now is the time to learn to debug > > routing problems. traceroute is the best starting place > > > I used traceroute to check whether the problematic node is accessible by > other machines. It just works - all except HDFS that it. > > Any way to check what causes this exception? > > Regards. > -- Alpha Chapters of my book on Hadoop are available http://www.apress.com/book/view/9781430219422
