[erlang-questions] {error,timeout} with gethostbyname

[info]

On Fri, Sep 25, 2009 at 12:03:38PM +0200, info wrote:
> Hi Raimo,
> Note that I appreciate your help because it seems that the problem is not in erlang.
> 
> On Thu, Sep 24, 2009 at 04:55:57PM +0200, info wrote:
>  > I also tried to add the address of my dns server.
>  > inet_db:add_ns({ip}).
>  > But no effect.
>  > 
>  > inet_getrc(). gives now:
>  > 
>  > [{host,{127,0,0,1},["my_host"]},
>  >  {nameserver,{192,168,1,33}}]
>  > 
> You have {res_lookup,[native,file]} meaning first is the OS
> gethostbyname equivalent function used. During the startup
> of Erlang it discovered that "my_host" could not be
> resolved so it entered "my_host" as {127,0,0,1} into the
> internal hosts table to ensure that inet:gethostbyname("my_host")
> would succeed.
> 
> But the native lookup method times out, probably due
> to misconfigured name resolving in the OS, so the
> internal hosts table is never used.
> 
> How long does the call inet:gethostbyname("my_host")
> take to return {error,timeout}?
>  > > > > > > > > > > > > 6-7 seconds

Ok...

> 
> Can the native lookup method look up any name at all?
> Try: inet_gethost_native:gethostbyname("localhost").
>  > > > > > > > > > > > > {error,timeout}
> inet_gethost_native:gethostbyname("my_host").
>  > > > > > > > > > > > > {error,timeout}
> inet_gethost_native:gethostbyname("www.google.com").
>  > > > > > > > > > > > > {error,timeout}

Nothing worked.

>  >From a Windows command shell, try:
> nslookup my_host
>  > > > > > > > > > > > >server: my_host.my_domain.local
>  > > > > > > > > > > > >address: 192.168.1.33
>  > > > > > > > > > > > >name: my_host.my_domain.local
>  > > > > > > > > > > > >address: 192.168.1.33
> nslookup localhost
>  > > > > > > > > > > > >server: my_host.my_domain.local
>  > > > > > > > > > > > >address: 192.168.1.33
>  > > > > > > > > > > > >my_host.my_domain.local doesn't find localhost: no existing domain (*** I translated from french ! )

Well well, of course that worked...
This means your host is its own DNS server (?).

> 
> Pay special attention to which nameserver that answers.
> 
> If you can not fix the network configuration, which will
> solve your problem, you can configure erlang to not
> use the native lookup method. The erlang DNS resolver
> client was much improved to R13B02, but it worked
> well in R13B01 too.
>  > > > > > > > > > > > >My problem is I don't see what is wrong in my network configuration or in my dns server configuration !
> Set the lookup method to [file,dns] and add your
> nameserver as you tried:
> inet_db:add_ns({192,168,1,33}).
>  > > > > > > > > > > > >ok
> inet_db:set_lookup([file,dns]).
>  > > > > > > > > > > > >ok
> Then try inet:gethostbyname("my_host"),
>  > > > > > > > > > > > >{ok,{hostent,"my-host",[],inet,4,[{127,0,0,1}]}}             BETTER !!

That is the patched 'file' lookup method that found the name.
This is often enough to run a local non-distributed node.

> or even inet_res:gethostbyname("my_host).
>  > > > > > > > > > > > >{error,timeout}                         WHY ?

Maybe your firewall does not allow DNS requests from erlang.
Try:
rr(inet_res).
+++++++
[connect_opts,dns_header,dns_query,dns_rec,dns_rr,hostent,
 listen_opts,sctp_opts,udp_opts]

inet_res:nslookup("my_host.my_domain.local", in, a, [{{192,168,1,33},53}]).
+++++++
{ok,#dns_rec{header = #dns_header{id = 2,qr = 1,opcode = 0,
                                  aa = 1,tc = 0,rd = 1,ra = 1,pr = 0,
                                  rcode = 0},
             qdlist = [#dns_query{domain = "my_host.my_domain.local",
                                  type = a,class = in}],
             anlist = [#dns_rr{domain = "my_host.my_domain.local",class = in,
                               type = a,cnt = 0,tm = undefined,ttl = 3600,
                               bm = [],
                               data = {192,168,1,33},
                               func = false}],
             nslist = [],arlist = []}}


And, maybe using the external IP address is what is not allowed.
inet_res:nslookup("my_host.my_domain.local", in, a, [{{127,0,0,1},53}]).
+++++++++
{ok,#dns_rec{header = #dns_header{id = 3,qr = 1,opcode = 0,
                                  aa = 1,tc = 0,rd = 1,ra = 1,pr = 0,
                                  rcode = 0},
             qdlist = [#dns_query{domain = "my_host.my_domain.local",
                                  type = a,class = in}],
             anlist = [#dns_rr{domain = "my_host.my_domain.local",class = in,
                               type = a,cnt = 0,tm = undefined,ttl = 3600,
                               bm = [],
                               data = {192,168,1,33},
                               func = false}],
             nslist = [],arlist = []}}
+++++++++++++
 inet_gethost_native:gethostbyname("www.google.com").                
{error,timeout}
inet_gethost_native:gethostbyname("localhost").                     
{error,timeout}
inet_gethost_native:gethostbyname("my_host").                      
{error,timeout}

DO YOU SEE A DIFFERENCE ?

> But I hope you can fix your network configuration instead...
> 
>  > 
>  > 
>  > n Wed, Sep 23, 2009 at 04:31:35PM +0200, info wrote:
>  >   > Hi all,
>  >   > On a windows 2003 server sbs this command returns {ok,"my_host"} :
>  >   > 
>  >   > {ok,N}=inet:gethostname().
>  >   > 
>  >   > But the following command returns {error,timeout} :
>  >   > 
>  >   > inet:gethostbyname(N).
>  >   > 
>  >   > On a Vista machine, the previous command returns a correct answer.
>  >   > 
>  >   > I know that it is not an erlang problem but if you could give me support, I will appreciate ;-)
>  > 
>  > Erlang may have problems configuring name lookups.
>  > Give me the output from ets:tab2list(inet_db).
>  > 
>  > Which erlang release are you running, it sounds like pre-R13B02?
>  > 
>  > Try starting with erl -name foo
>  > and do the same, ets:tab2list/1 too.
>  > 
>  > -- 
>  > 
>  > / Raimo Niskanen, Erlang/OTP, Ericsson AB
> 
> -- 
> 
> / Raimo Niskanen, Erlang/OTP, Ericsson AB

-- 

/ Raimo Niskanen, Erlang/OTP, Ericsson AB