Help! Need expert advice on IP resolution

Help! Need expert advice on IP resolution

Post by bailey » Fri, 31 Jan 1997 04:00:00



Hi!

I am trying to figure out how a client server program our company uses
operates.

The client part of the program communicates with the server via TCP/IP.
When a connection is established, I can see the server's IP address
listed at the top of the program's screen.  Additonally, the client has
its own TCP/IP address.

BUT!!!  During the client setup, I never have type in the IP of its
server.  It seems that the client, in some unknown fashion, resolves the
server's IP address.

My question is how?  What protocol could possible allow this?  DNS comes
to mind for me.  However, I know for a fact that this C/S program does
not use DNS.  What could be facilitating the IP resolution of the server
for the client?

Any help on this would be GREATLY appreciated.

Additionally, do any of you know of a good free IP sniffer available for
IBM PCs?

Thanks!
Francis Yom

 
 
 

Help! Need expert advice on IP resolution

Post by Tony L » Fri, 31 Jan 1997 04:00:00


Quote:> The client part of the program communicates with the server via TCP/IP.
> When a connection is established, I can see the server's IP address
> listed at the top of the program's screen.  Additonally, the client has
> its own TCP/IP address.

> BUT!!!  During the client setup, I never have type in the IP of its
> server.  It seems that the client, in some unknown fashion, resolves the
> server's IP address.

> My question is how?  What protocol could possible allow this?  DNS comes
> to mind for me.  However, I know for a fact that this C/S program does
> not use DNS.  What could be facilitating the IP resolution of the server
> for the client?

Are you _certain_ that it's not using DNS?  Almost all systems do these
days.  And it need not appear explicitly anywhere in the program.  For
example, the runtime library or winsock library may be using DNS.  Other
alternatives are NIS (NIS+ -- bleah), or good ol' /etc/hosts tables.  Or
it could be hard-coded.  

Can't tell without being there...

Tony

 
 
 

Help! Need expert advice on IP resolution

Post by Barry Margol » Sat, 01 Feb 1997 04:00:00




>BUT!!!  During the client setup, I never have type in the IP of its
>server.  It seems that the client, in some unknown fashion, resolves the
>server's IP address.

Perhaps the client sends out a broadcast, and the server is expected to
respond to this.

Note that this will generally only work when the client and server are on
the same subnet, as broadcasts are not normally forwarded by routers
(although they can be configured to do so in various ways, e.g. Cisco's
"helper-address" feature).
--
Barry Margolin
BBN Corporation, Cambridge, MA

(BBN customers, call (800) 632-7638 option 1, not my direct #, for support)

 
 
 

Help! Need expert advice on IP resolution

Post by Kok Fock Sen » Tue, 04 Feb 1997 04:00:00



> Hi!

> I am trying to figure out how a client server program our company uses
> operates.

> The client part of the program communicates with the server via TCP/IP.
> When a connection is established, I can see the server's IP address
> listed at the top of the program's screen.  Additonally, the client has
> its own TCP/IP address.

> BUT!!!  During the client setup, I never have type in the IP of its
> server.  It seems that the client, in some unknown fashion, resolves the
> server's IP address.

> My question is how?  What protocol could possible allow this?  DNS comes

Well, there is a lot of way this can be done. It depends on the design
od the C/S program. They may share a common file on the network,
whenever the server start up, it will add his entry to it. The client
just read from this file.
Well more dynamic way is the server program has the ability to listen
to client's request like this :
Whenever a client starts up, it broadcasta a data packet to everybody
on the network asking something like : "Who can serve me as XXX server?"
The server who receive this packet just reply to the client "Yes I do."
 That 's it. It's easy to implement in the program.
Quote:> to mind for me.  However, I know for a fact that this C/S program does
> not use DNS.  What could be facilitating the IP resolution of the server
> for the client?

> Any help on this would be GREATLY appreciated.

> Additionally, do any of you know of a good free IP sniffer available for
> IBM PCs?

I am looking for this kind of sniffer as well.

- Show quoted text -

Quote:

> Thanks!
> Francis Yom

 
 
 

Help! Need expert advice on IP resolution

Post by baile » Fri, 07 Feb 1997 04:00:00


Dear Seng,

Thank you for your reply to my post.  I'm still working out all the details, but I found a
sniffer.

You can pick up a freeware DOS ethernet sniffer at:

ftp://ftp.germany.eu.net/pub/networking/inet/ethernet/

Hope this helps!
Francis

 
 
 

Help! Need expert advice on IP resolution

Post by Ravin Asa » Sat, 08 Feb 1997 04:00:00



Quote:> Hi!

> I am trying to figure out how a client server program our company uses
> operates.

> The client part of the program communicates with the server via TCP/IP.
...
> to mind for me.  However, I know for a fact that this C/S program does
> not use DNS.  What could be facilitating the IP resolution of the server
> for the client?

..

If I understand your terminology, the "client" program is an application program that communicates with a "server" application on the other box.  If so, the client piece is probably operating on top of a TCP/IP stack.  This could be something like NetManage's Chameleon, or even the bundled Microsoft TCP/IP stack in WIndows95 or NT. It is that stack that is probably configured to use DNS/BIND. The client application simply sends a resolver query to the TCP/IP stack.

-Ravin
-----------------------------------------------------------
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   Group Leader - Open Systems |   Fax: (630) 719-0492

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