what does h_error=4 mean???

[Kevin Darcy]

If you're checking MX records, why are you doing a
gethostbyname()? gethostbyname() only checks for A records (and, indirectly,
CNAMEs, of course).

Perhaps you should write your own specialized resolver for this. Or steal the
code from sendmail. Or just use the Perl Net::DNS module.

It's not surprising in the least that you're getting h_errno=4. What it means
is that the name exists, but no record of the requested type (i.e. A) is owned
by the name. If someone defines an MX record for a name, but no A record,
you'll get h_errno=4.


- Kevin

Guðbjörn Hreinsson wrote:

> This is probably more of a resolver issue but hope that the
> bind-users is an appropriate medium for this question.
>
> I have intermittent errors with some domains that result in
> h_error=4...
>
> I have a messaging software that does a check of the MAIL FROM
> address and checking that the domain part has mx server defined.
>
> Some domains result in h_error=4 which according to the man
> page for gethostbyname means NO_ADDRESS and
>
>     The requested name is valid but does not
>     have an IP address; this is not a
>     temporary error.  This means another type
>     of request to the name server will result
>     in an answer.
>
> but I am not sure what this error indicates and how one is
> supposed to deal with it?
>
> I have the folowing c program as a test:
>
>     #include <sys/types.h>
>     #include <sys/socket.h>
>     #include <netdb.h>
>     #include <errno.h>
>
>     struct hostent *gethostbyname();
>
>     struct hostent *hp;
>     extern int h_errno;
>
>     main(argc,argv)
>     int argc;
>     char *argv[];
>     {
>        int i;
>        if (argc > 1) {
>           for (i = 1; i < argc; i++) {
>              hp = gethostbyname(argv[1]);
>              if (!hp)
>              printf("%s failed, h_errno=%d errno %d\n", argv[i], h_errno,
>              \
>                         errno);
>              else
>              printf("name = %s, h1 = %x\n", hp->h_name, hp->h_addr_list[0]);
>           }
>        }
>     }
>
> beware of the \ which is only because my email client would
> wrap it...
>
> Is this wrong? Should I call something else/differently in case of
> h_error=4?
>
> Rgds,
> -GSH