[erlang-questions] Problems when running distributed pingpong

Raimo Niskanen <>
Thu Oct 7 10:17:28 CEST 2010


Hi.

Regarding name resolution Windows and MacOS X are two rather
irregular platforms for Erlang. Congratulations.

There are lots of tricks you can do by configuring Erlang's name
resolution to compensate for environment glitches. See:
    http://www.erlang.org/doc/apps/erts/inet_cfg.html
What often happens when you take this path is that all other
tools in the OS thinks differently about name resolution
and in a product that can be a problem.

Changing the hosts file is a way to reconfigure the
native resolver for the whole machine but only that machine.
When more than one machine is involved you probably want
to use what is in their common name resolving service.

This is a trick that should work using strange longnames:

erl -name 

erl -name 

1> net_adm:ping('').


You should also be able to use the working name like this:

erl -name 

erl -name 

1> net_adm:ping('').


Both sides of the connection must aggree on their hostnames,
and the hostname must work for creating the connection.



To help debug your problem at hand the output of these is of interest:
2> io:format("~p.~n", [ets:tab2list(inet_db)]).
3> io:format("~p.~n", [ets:tab2list(inet_hosts_file_byname)]).
4> io:format("~p.~n", [ets:tab2list(inet_hosts_byname)]).
5> inet_gethost_native:gethostbyname("dyn-95-175-140-20").
6> inet_gethost_native:gethostbyname("dyn-95-175-140-20.inuknetworks.com").
7> inet_gethost_native:gethostbyname("dyn-95-175-140-20.chaledi.unite.inuknetworks.com").


On Thu, Oct 07, 2010 at 12:19:55AM +0100, Jiansen He wrote:
> I tried adding both lines to both machines.  It still doesn't work.
> Besides, can I bind two host names to the same IP in the same line?  It
> doesn't looks like the form of sample binding.
> 
> In addition, instead of changing the hosts file, could I "locally" change
> the IPs/hostnames binding inside erlang?
> 
> Regards
> Jiansen
> 
> 
> 
> On Wed, Oct 6, 2010 at 8:04 PM, Ahmed Omar <> wrote:
> 
> > Yes, you could try adding both machines IPs/hostnames combinations there
> > so something like :
> > 95.175.140.5    dyn-95-175-140-3        dyn-95-175-140-3.inuknetworks.com
> >
> > 95.175.140.3    dyn-95-175-140-5        dyn-95-175-140-5.inuknetworks.com
> >
> >
> > On Wed, Oct 6, 2010 at 8:53 PM, Jiansen He <>wrote:
> >
> >>
> >> Windows
> >>
> >> # Copyright (c) 1993-2009 Microsoft Corp.
> >> #
> >> # This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
> >> #
> >> # This file contains the mappings of IP addresses to host names. Each
> >> # entry should be kept on an individual line. The IP address should
> >> # be placed in the first column followed by the corresponding host name.
> >> # The IP address and the host name should be separated by at least one
> >> # space.
> >> #
> >> # Additionally, comments (such as these) may be inserted on individual
> >> # lines or following the machine name denoted by a '#' symbol.
> >> #
> >> # For example:
> >> #
> >> #      102.54.94.97     rhino.acme.com          # source server
> >> #       38.25.63.10     x.acme.com              # x client host
> >>
> >> # localhost name resolution is handled within DNS itself.
> >> #    127.0.0.1       localhost
> >> #    ::1             localhost
> >>
> >>
> >> Mac
> >>
> >> ##
> >> # Host Database
> >> #
> >> # localhost is used to configure the loopback interface
> >> # when the system is booting.  Do not change this entry.
> >> ##
> >> 127.0.0.1    localhost
> >> 255.255.255.255    broadcasthost
> >> ::1             localhost
> >> fe80::1%lo0    localhost
> >>
> >>
> >> Shall I write something to the host file?
> >>
> >> Many thanks
> >> Jiansen
> >>
> >>
> >>
> >>
> >>
> >> On Wed, Oct 6, 2010 at 7:16 PM, Ahmed Omar <> wrote:
> >>
> >>> It seems to me like a problem with your hosts file (on Mac /etc/hosts, on
> >>> windows %systemroot%\system32\drivers\etc\ )
> >>>
> >>> could you please post it here?
> >>>
> >>> On Wed, Oct 6, 2010 at 5:22 PM, Jiansen He <>wrote:
> >>>
> >>>> net:gethostbyaddr('95.175.140.20').
> >>>>
> >>>
> >>>
> >>>
> >>> --
> >>> Best Regards,
> >>> - Ahmed
> >>> http://nl.linkedin.com/in/adiaa
> >>>
> >>
> >>
> >
> >
> > --
> > Best Regards,
> > - Ahmed
> > http://nl.linkedin.com/in/adiaa
> >

-- 

/ Raimo Niskanen, Erlang/OTP, Ericsson AB


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