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From: kcw3388 on 16 Jun 2006 22:25
Hi,

I have a AIX 5.3 machine; the
gethostbyaddr ( ) and nslookup failed.

I have the correct entry in /etc/hosts file.

But the "host" command worked fine.

Does anyone why?

Also, is there any C library call similar
to "host" command on AIX?

Any comments/suggestions are appreciated.

Thanks,

Kevin

From: Reiner Huober on 17 Jun 2006 01:47

kcw3388(a)hotmail.com schrieb:

> Hi,
>
> I have a AIX 5.3 machine; the
> gethostbyaddr ( ) and nslookup failed.
>
> I have the correct entry in /etc/hosts file.
>
> But the "host" command worked fine.
>
> Does anyone why?
>
> Also, is there any C library call similar
> to "host" command on AIX?
>
> Any comments/suggestions are appreciated.
>

nslookup will never search in /etc/hosts, it is the nameserver lookup
and consults /etc/resolv.conf and *only* DNS servers.

gethostbyaddr consults many sources, e.g. /etc/hosts, NIS, DNS. On most
systems, /etc/nsswitch.conf must be set appropriately - I do not know
modern AIX. The address of a host in /etc/hosts should be recognizable.


However, if you use DNS, a special domain (hierarchy) *in-addr.arpa."
is consulted. The addresses are not type PTR So if you want to search
the address 1.2.3.4, you must use type=PTR and 4.3.2.1.in-addr.arpa.
Some modern versions of nslookup do this automatically if you enter an
IP address, but not all. Use "dig" instead. The address to host name
resolution in DNS works only if the administrator also makes correct
entriess in the in-addr.arpa.-domain.

> Also, is there any C library call similar
> to "host" command on AIX?
>
> Any comments/suggestions are appreciated.
>

I bet that the host command uses gethostbyaddr. Are you sure that you
used the correct paramenters. Note that gethostbyaddr does not accept
an address as (char*), e.g. "1.2.3.4" as parameter. This is often not
detected since the first parameter is declared as (void*). You must use
the macro inet_addr and supply a 32 entity casted to void* or char* :-(

Do not use gethostbyaddr("1.2.3.4",strlen("1.2.3.4"), AF_INET), but
instead

struct in_addr a;
a.s_addr=inet_addr("1.2.3.4");
gethostbyaddr((char*)&a,sizeof(a),AF_INET)

This works on my MacOS X box (shoud work for you too)

include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

main(argc,argv)
int argc; char ** argv;
{ struct hostent * h;
struct in_addr a;

a.s_addr=inet_addr(argc>1 ? argv[1] : "");
h=gethostbyaddr((char*)&a,sizeof(a),AF_INET);
printf("%s\n",h ? h->h_name : "not found");
}

HTH
Hubble.

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