If one of the name servers is down, the tool crashes completely. May be add an option to have just a warning? ``` % ./ns-tree.py cyberstructure.fr Traceback (most recent call last): File "/home/stephane/tmp/ns-tree/./ns-tree.py", line 163, in <module> tree.build() File "/home/stephane/tmp/ns-tree/./ns-tree.py", line 27, in build node.create_edges( self.nodes ) File "/home/stephane/tmp/ns-tree/./ns-tree.py", line 99, in create_edges ns_zone = get_zone_name( ns ) ^^^^^^^^^^^^^^^^^^^ File "/home/stephane/tmp/ns-tree/./ns-tree.py", line 129, in get_zone_name ans = dns.resolver.resolve( qname, dns.rdatatype.SOA, raise_on_no_answer=False ) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3/dist-packages/dns/resolver.py", line 1565, in resolve return get_default_resolver().resolve( ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3/dist-packages/dns/resolver.py", line 1321, in resolve timeout = self._compute_timeout(start, lifetime, resolution.errors) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3/dist-packages/dns/resolver.py", line 1075, in _compute_timeout raise LifetimeTimeout(timeout=duration, errors=errors) dns.resolver.LifetimeTimeout: The resolution lifetime expired after 5.401 seconds: Server Do53:192.168.2.254@53 answered The DNS operation timed out.; Server Do53:192.168.2.254@53 answered The DNS operation timed out.; Server Do53:192.168.2.254@53 answered The DNS operation timed out. ```