Hostname resolution fails using zeroconf

Problem

Using the zeroconf discovery, SyncThread on local host hostfoo throws errors about being unable to resolve the hostname of a remote host hostbar:

[INFO][rosout]: hostbar is now online
[INFO][rosout]: SyncThread[hostfoo] Requesting remote state from 'http://hostbar:11911/'
[ERROR][rosout]: SyncThread[hostfoo] ERROR: Traceback (most recent call last):
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/master_sync_fkie/sync_thread.py", line 264, in _request_remote_state
    remote_state = remote_monitor.masterInfo()
  File "/usr/lib/python2.7/xmlrpclib.py", line 1243, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1602, in __request
    verbose=self.__verbose
  File "/usr/lib/python2.7/xmlrpclib.py", line 1283, in request
    return self.single_request(host, handler, request_body, verbose)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1311, in single_request
    self.send_content(h, request_body)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1459, in send_content
    connection.endheaders(request_body)
  File "/usr/lib/python2.7/httplib.py", line 1053, in endheaders
    self._send_output(message_body)
  File "/usr/lib/python2.7/httplib.py", line 897, in _send_output
    self.send(msg)
  File "/usr/lib/python2.7/httplib.py", line 859, in send
    self.connect()
  File "/usr/lib/python2.7/httplib.py", line 836, in connect
    self.timeout, self.source_address)
  File "/usr/lib/python2.7/socket.py", line 557, in create_connection
    for res in getaddrinfo(host, port, 0, SOCK_STREAM):
gaierror: [Errno -2] Name or service not known

Notes:

• There is no network-wide name resolution, I want to rely on mdns only.
• It’s an IPv6-only network

Debugging

My /etc/nsswitch.conf (relevant line):

hosts:          files mdns [NOTFOUND=return] dns

The parameters for the zeroconf node are default; the zeroconf nodes discover each other perfectly.

Manual hostname resolution fails with:

host hostbar
host hostbar.local
avahi-resolve -n hostbar
getent hosts hostbar

Manual hostname resolution works with:

avahi-resolve -n hostbar.local
getent hosts hostbar.local

I’m not sure, it might be a better idea to use hostbar.local instead?

[atiderko]

I added a fqdn parameter. You have to set this parameter to true.

rosrun master_discovery_fkie zeroconf _fqdn:=true

Regarding your post, I’m afraid that the ROS-topic communication will not work anyway. But you can try it out!

[stertingen]

Well, it’s not that undocumented: http://www.ros.org/news/2012/06/ipv6-support-for-ros-nodes.html