Hi -

I'm having difficulties with some old sockets software of mine.
gethostbyaddr is returning null for some valid IP addresses.

Here's my code:

hostAddress = inet_addr( argv[1] );
if( hostAddress == INADDR_NONE )
{
hostEntry = gethostbyname( argv[1] );
if( !hostEntry )
{
printf( "name not found\n" );
return 0;
}
}
else
{
hostEntry = gethostbyaddr( (char*) &hostAddress, sizeof( hostAddress ),
AF_INET );
if( !hostEntry )
{
printf( "gha failed %d\n", h_errno );
return 0;
}

}

which I thought was fairly non-controversial.

if argv[1] is 10.242.0.88, gethostbyaddr returns 0, and h_errno is 1
(HOST_NOT_FOUND).

I can get to 10.242.0.88 via telnet and other programs, and traceroute can
find it. (2 hops).

The aix 5.2 box I'm on is on a different subnet - for the sake of argument,
80.229.*, so it's ip would be 80.229.44.23.

The program can find other 80.229.* addresses, and if I put 10.242.0.88 in
/etc/hosts, it works.

So what am I doing wrong?

(Should I be doing gethostbyaddr at all? I thought it was the correct way to
get a hostent structure from an IP address.)

cheers,
clive

In article <4300f18d$0$1295$ed2619ec@ptn-nntp-reader02.plus.net>,
Clive George <clive@xxxx-x.fsnet.co.uk> wrote:
....
>if argv[1] is 10.242.0.88, gethostbyaddr returns 0, and h_errno is 1
>(HOST_NOT_FOUND).
....
>The program can find other 80.229.* addresses, and if I put 10.242.0.88 in
>/etc/hosts, it works.

What you write after the "and if I put" in your last sentence makes
me wonder: what result do you get (when your "gethostbyaddr" call
returns HOST_NOT_FOUND), from the command "nslookup 10.242.0.88"?

--
Ken Bell :: kenbell_AT_panix_DOT_com :: 212-475-4976 (voice)

"Ken Bell" <kenbell@panix.com> wrote in message
news:ddrf98$qeh$1@reader2.panix.com...
> In article <4300f18d$0$1295$ed2619ec@ptn-nntp-reader02.plus.net>,
> Clive George <clive@xxxx-x.fsnet.co.uk> wrote:
> ...
>>if argv[1] is 10.242.0.88, gethostbyaddr returns 0, and h_errno is 1
>>(HOST_NOT_FOUND).
> ...
>>The program can find other 80.229.* addresses, and if I put 10.242.0.88 in
>>/etc/hosts, it works.
>
> What you write after the "and if I put" in your last sentence makes
> me wonder: what result do you get (when your "gethostbyaddr" call
> returns HOST_NOT_FOUND), from the command "nslookup 10.242.0.88"?

It fails :

Server: dns.mydomain.com
Address 80.229.123.1

*** dns.mydomain.com can't find 10.242.0.88:Non-existent host/domain

(it isn't actually mydomain...)

Does this mean I shouldn't be using gethostbyaddr in my code? How do other
sockets programs get the hostent structure from an IP address? (since they
do appear to work.)

cheers,
clive

Hi Clive...

"Clive George" <clive@xxxx-x.fsnet.co.uk> wrote in message news:4301bd1b$0$17459$ed2e19e4@ptn-nntp-reader04.plus.net...
> > ...
> >>if argv[1] is 10.242.0.88, gethostbyaddr returns 0, and h_errno is 1
> >>(HOST_NOT_FOUND).
> > ...
> >>The program can find other 80.229.* addresses, and if I put 10.242.0.88 in
> >>/etc/hosts, it works.
> >
> > What you write after the "and if I put" in your last sentence makes
> > me wonder: what result do you get (when your "gethostbyaddr" call
> > returns HOST_NOT_FOUND), from the command "nslookup 10.242.0.88"?
>
> It fails :
>
> Server: dns.mydomain.com
> Address 80.229.123.1
>
> *** dns.mydomain.com can't find 10.242.0.88:Non-existent host/domain
>
> (it isn't actually mydomain...)
>
> Does this mean I shouldn't be using gethostbyaddr in my code? How do other
> sockets programs get the hostent structure from an IP address? (since they
> do appear to work.)

Sounds as though you need to *either* configure the 10.242.0.88 host's name, if this is something you control, in the name-server or
/etc/hosts, *or* not use the gethostby? functions which invoke the call to the name-server to translate between name and address.
I'm no expert in sockets programming but I have worked with TCP/IP for a number of years.

--
Regards,
Tim Clarke (a.k.a. WBST)

"Tim Clarke" <SpamBlock.Monetaim.Com@cswebmail.com> wrote in message
news:WqjMe.10624$1F5.9394@newsfe4-win.ntli.net...

>> Does this mean I shouldn't be using gethostbyaddr in my code? How do
>> other
>> sockets programs get the hostent structure from an IP address? (since
>> they
>> do appear to work.)
>
> Sounds as though you need to *either* configure the 10.242.0.88 host's
> name,
> if this is something you control, in the name-server or /etc/hosts, *or*
> not
> use the gethostby? functions which invoke the call to the name-server to
> translate between name and address.
> I'm no expert in sockets programming but I have worked with TCP/IP for a
> number of years.

Darn, yes, have looked at my code a little more carefully, and no, I don't
need to use gethostbyaddr at all - I don't need the hostent. I suspect this
is a hangover from some of my early attempts at sockets programming.

cheers,
clive