RE: For Scott Klement: Re: get host IP address -- MIDRANGE-L

Actually, the answer is of course, assuming the client has a connection to the 
server.  The server has to have to IP address of the client in order to 
communicate.

Now if instead of DHCP, you meant that the router does NAT'ing then the answer 
is indeed "of course not".  Unless there is some method by which the server can 
interrogate the router's internal NAT table.

HTH,

Charles Wilt
--
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
 

> -----Original Message-----
> From: midrange-l-bounces@xxxxxxxxxxxx
> [mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of Shannon O'Donnell
> Sent: Thursday, September 01, 2005 2:23 PM
> To: midrange-l@xxxxxxxxxxxx
> Subject: For Scott Klement: Re: get host IP address
> 
> 
> Hey Scott,
> 
> i'm guessing that the answer to this is "Of course  not!"... 
> But, is there any way to retrieve/know the ip adress of a 
> client workstation that is behind a router which uses dhcp?
> 
> I have a situation where calling qdcrevd does not work to 
> return the actual pc ip address because the workstation is 
> communicating with the iseries first through a local router 
> which has dhcp and its own firewall and then across the 
> internet to the iseries.
> 
> -----Original Message-----
>     From: "Scott Klement"<midrange-l@xxxxxxxxxxxxxxxx>
>     Sent: 9/1/05 12:06:43 PM
>     To: "Midrange Systems Technical 
> Discussion"<midrange-l@xxxxxxxxxxxx>
>     Subject: Re: get host IP address
>     
>     > I've gone through the archives and it seems that the 
> recommended way to get
>     > local host IP address is via gethostbyname function call.
>     
>     Not this again!
>     
>     gethostbyname() looks up an IP address for an internet 
> domain name.  It 
>     searches your local "HOSTS TABLE" and it also searches 
> DNS.  Whether or 
>     not this will actually give you your "local host IP 
> address" is entirely 
>     dependent on whether you have a domain name that can be 
> looked up to find 
>     it in DNS.
>     
>     It's not a smart way to approach the problem, and unless 
> you're in control 
>     of how DNS is set up. you shouldn't expect it to work.
>     
>     Furthermore, you don't assign an IP address to a host. 
> You assign an IP 
>     address to a network interface.  Sometimes, you even 
> assign more than one 
>     IP address to a network interface.
>     
>     Consequently, the "right way" to find out the IP address 
> really depends on 
>     what you want to use it for.
>     
>     Consider the scenario of an iSeries system (actually, 
> this is true for all 
>     computers, not just the iSeries) who is connected to two 
> different 
>     ethernet LANs, plus a dial-up to the internet.  There are 
> a minimum of 4 
>     different IP addresses assigned to this iSeries:
>     
>     
>     127.0.0,1 -- this IP address is always present, and it's 
> used when one
>                   program on the system wants to communicate 
> with another one
>                   on the same system.
>     
>     
>     One is associated with the dial-up (Point to Point) 
> interface for talking
>     to the internet, and will most likely change with each connection.
>     
>     One is associated with each of the LAN interfaces.
>     
>     
>     So now you have 4 IP addresses?  which one is the "Right one"?
>     
>     Well, if you're talking to another program on the same 
> system (such as 
>     using FTP to move a file from one place to another, or to 
> print a stream 
>     file from a batch job) it's safe to hardcode 127.0.0.1.  
> The nice thing 
>     about this interface is that it's very fast, very secure 
> (since it's only 
>     accessible from within the same system) and it'll always 
> be there with the 
>     same address on every computer that your software gets 
> installed on.
>     
>     If you're trying to "talk-back" to a 5250 client that has 
> connected, 
>     you'll need to find out which network interface they've 
> come in through. 
>     The QDCRDEVD API is able to tell you the IP address of 
> the "local" network 
>     interface that they used.
>     
>     If you're writing a program that communicates over a 
> TCP/IP network, the 
>     getsockname() API can be used to find out the IP address 
> of the interface 
>     that the system routed your request through.
>     
>     If you're simplying trying to look this up for the 
> purposes of printing it 
>     on a report or keeping track of it for auditing purposes 
> or something like 
>     that, you'll want to keep track of ALL of the IP 
> addresses on the system.
>     
>     I wrote a demonstration program that lists all of the IP 
> addresses on the 
>     system (though, you could modify it to only list a 
> particular network 
>     interface if you wanted to) that you can download from 
> the following link:
>     
>     
> http://www.iseriesnetwork.com/noderesources/code/clubtechcode/
> DspIpIfc.zip
>     
>     
>     -- 
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