All about the DHCP server callout API functions.

re: All about the DHCP server callout API functions.

Kevin Marquette — Fri, 25 Feb 2005 23:37:00 GMT

I have looked for this before, I just didn't know what to search for.

I have looked for scripting dhcp, loading dhcp as a ActiveX control, and commandline access. And I never found what I was looking for.

I was wanting to track DHCP requests and limit who is to receive them. This is exactly what I needed.

other questions. How would this work with VB.NET? I probably shouldn't write DHCP dll's in managed code, but VB is our standard language. Would it be easyer to write a wrapper in C++ to let me do the work in VB.NET? Any thoughts?

What about running 2 DHCP Servers on the same box and loading custom DLL's. I want one group of computers to get one ip range and another to get a different range. Would that be possible, or am I dreaming.

re: All about the DHCP server callout API functions.

Kevin Marquette — Sun, 27 Feb 2005 10:03:00 GMT

re: All about the DHCP server callout API functions.

A.J.Anto — Sun, 27 Feb 2005 13:08:00 GMT

I guess you can write C++ wrapper arround the managed code. This should be possible.
Other than that, I don't know why you should be running two DHCP servers on the same box. If all you wanted to acheive was to make sure that computers belonging to two distinct groups are allocated an IP address from two distinct ranges (scopes in DHCP terminology), I am afraid that this is not possible today. The reason why this is not possible today is that the DHCP server chooses a scope from which it doles out an IP address based only on the subnet where the client is existing. This is done so that the machine gets an address that is appropriate to the link.

re: All about the DHCP server callout API functions.

Kevin Marquette — Mon, 28 Feb 2005 00:07:00 GMT

I have an idea that should work in theory.

I want to give a scope to all authorized computers and a private scope to all others.
The computers will exist on the same physical network, but on different subnets.

I do have a reason for my madness

re: All about the DHCP server callout API functions.

A.J.Anto — Tue, 01 Mar 2005 17:42:00 GMT

I guess you can do that. But for this you must sort of hack the packet pointer variable 'Packet' got in the the function DhcpNewPktHook. You can overwrite the giaddr field in the packet buffer to the subnet address of the scope from which you want to assign the IP address. Say for unauthenticated computers you might want to allocate addresses from scope 192.168.200.0 then you might want to overwrite the giaddr field to 192.168.200.1 to fool the server that this packet had come from the segment 192.168.200.0 and hence we must allocate the address from that scope. This is in accordance with the RFC 2131. This is fine but this involves parsing the packet which is a BYTE *. I really don't know if this will work. Have not tried it myself. The possible issues that might arise is that: if the packet origanally comes from the local network on which the DHCP server is attached then the DHCP server might send the resonse in a different way than when the packet orignates from the remote network as we are feingning it.

re: All about the DHCP server callout API functions.

A.J.Anto (On behalf of Rob White) — Thu, 10 Mar 2005 19:45:00 GMT

Hi,

I've just read your article http://weblogs.asp.net/anto_rocks/archive/2005/02/25/380510.aspx, I built the dll from your source code and installed it on my server, sure enough up popped the event number 1033, it seemed that everything went well. Now I paused, and resumed my server, to check it was working correctly, but the text file callout.txt remained blank. I've also been playing with DhcpEnumSubnetClients, with equally low success rates. Both your dll and the code I wrote to make use of the DhcpEnumSubnetClients function look like they should work, but both are returning nothing.

Is there something that I need to install on my server? (it's a windows 2003 server, if that makes any difference) Is there a redistributable or some such that I need to install?

Any help would be gratefully received.
Regards,
Rob

re: All about the DHCP server callout API functions.

A.J.Anto — Thu, 10 Mar 2005 19:52:00 GMT

You do not need anything further than a Win2K3 server. I assume the file was created by the DHCP server but you don't see anything there. I don't get understand why this should be happening. Maybe we are missing something. Did u change the registry? Maybe there is someone else in the blogosphere who can help Rob??

re: All about the DHCP server callout API functions.

Tom Handerkin — Fri, 18 Mar 2005 23:19:00 GMT

This is what I obtained. Can you explain this?

Value obtained from file system volume descriptor pointer: 0x347cb00
The old setting was THU JAN 01 00:00:00 1970
Accepted system dates are greater than THU DEC 27 00:00:00 1990
ramdrv:/ - Volume is OK
tffsdrv: DOS mounting Complete
tffsdrv:/ - Volume is OK
nvdrv: DOS mounting Complete
nvdrv:/ - Volume is OK
0x34b97c8 (tStartup): WARNING: RAM db is deleted

re: All about the DHCP server callout API functions.

Qflash — Tue, 24 May 2005 10:07:28 GMT

RePost:
http://www.yeyan.cn/Programming/DHCPServerAPIfunctions.aspx

re: All about the DHCP server callout API functions.

anto_rocks — Tue, 24 May 2005 11:34:26 GMT

check out this: http://blogs.msdn.com/anto_rocks/archive/2005/05/24/421353.aspx

re: All about the DHCP server callout API functions.

JPawlak — Tue, 31 May 2005 03:59:57 GMT

Does anyone know how to dissect the lpbyte packet parameter and get the hostname requesting the IP address?

Thanks.

re: All about the DHCP server callout API functions.

Neal Ridgeway — Mon, 06 Jun 2005 19:42:28 GMT

Wow, I have finally found someone doing something with the callout.
I have had the callout running for sometime now on a Windows 2K3 server in the lab pumping out all kinds of good stuff.
My plan is to set up a parameter and reject those machines that dont pass the various test such as minimum patch level and virus pattern files.
The DLL was easy, the hard part has been the "back end" stuff.

re: All about the DHCP server callout API functions.

Tian Qiang Chen — Thu, 22 Dec 2005 06:30:17 GMT

Hello,

I'm lucky to find the article and the web site. It is very useful for me to develop an external dll of a DHCP server.

I am planing to reject to offer address to some machine. How can I do it?

Thanks

re: All about the DHCP server callout API functions.

Timrza.Chen — Thu, 05 Jan 2006 09:20:07 GMT

well, DhcpNewPktHook may fit your needs,

set the (LPBOOL ProcessIt) flag with FALSE, DHCP will drop the packet, you can add your own judgement to process it. be care LPBOOL. it is a point;

Thank you

Useful blog — Thu, 23 Feb 2006 03:37:52 GMT

Very nice blog!

re: All about the DHCP server callout API functions.

Juan Segura — Fri, 24 Mar 2006 18:28:35 GMT

I want to assign IPs from a different pools depending on the network card.

I have a W2K3 server with 4 network cards and I want a range of IPs for every card. I conect a group of clients to every card and I can know what group of clients belong with the IP of the client in a proxy application.

I can make the DLL in VS2005 C#?

GREAT!!!

re: All about the DHCP server callout API functions.

ratna — Wed, 05 Apr 2006 10:11:46 GMT

I ave included the callout.dll in windows2003 server.everthing sems to be fine but the dll is not able to log the messages when a new client request for an ipaddress from DHCP server.

please help

re: All about the DHCP server callout API functions.

Mazdisna Meenavee Mehr — Wed, 10 May 2006 10:54:15 GMT

Hi
Dear
I want to use your method that is a very good
way to have an extention to DHCP
But when I make this DLL in VC++.Net 2003 and make regitery changes I have a very bad Error
1034 : The sepscified procedure could not bE found
My server Is Win 2003
and i dont know exactly where i should paste your code sample
I make an Class Lib in VC++.Net 2003 and paste the sample code in cpp file what is wrong
Please Help Me?
Please
Best regards
Meenavee

Modify responses

Scrappy — Sun, 11 Jun 2006 01:37:25 GMT

I have taken a looka t using the DHCP call out but I need some assistants in tryin to determine how to manipulate the response. I understan I need to modify the packet contents before being sent. Again I think I need to use the call out DhcpNewPktHook. I can not figure out how to refrenece the portion of the packet?
Any quick sample on how to make this call? or perhaps does someone know who might help. All I want is help on changing various response fields such as gateway & mask values. Please help I am my witts end.

Cheers,
Scrappy

re: All about the DHCP server callout API functions.

Matthew Bailey — Thu, 15 Jun 2006 20:18:16 GMT

I work at an ISP and I am trying to use these API functions to migrate our DSL Customers from Static IP's to DHCP. In order for me to sell this the transition must be seamless. Our Router will append Option 82 which contains the ATM Virtual Circuit that is assigned to the customer. I have a working DLL that will disect the packet and get the Virtual Circuit information out, and then it will Query our MySQL database to reference ther Virtual Circuit to there old Static IP. Now all I need to do is send the IP that I get from the Database, how can I do this, should I use DHCPPacketSendHook?

Packet hooks in C#.Net

Phil — Tue, 18 Jul 2006 10:53:27 GMT

Hi, this is certainly the most useful BLOG on the subject. Thanks Anton.

Is it possible to hook into the server callout functions using c#.net or vb.net? Is so , how do I call it?

phil

Introducing a callout DLL ;)

Oliver — Sun, 27 Aug 2006 17:56:50 GMT

Hi,

the "restrict clients" feature was one thing that bugged me back in 2003, so I wrote a Delphi callout DLL for the MS DHCP server back then. Although it performed quite well, I decided to port it to C at some point and enhance it a little. The result is MACkerer2 and you can read about it here:
http://blog.assarbad.info/20060814/mackerer_en/

The whole idea is to limit the clients by their MAC addresses, which are stored in an Apache-like configuration file. There are advanced logging features that will blow your mind if you would like to give a certain context to the IP/MAC (i.e. lease) that was given out on 3rd of May 2004, for example. If you have given the respective information in the configuration file, it will be contained in the log file. Logging features can be turned on and off ...

The tool (i.e. the DLL) is OpenSource under the BSD license which allows anyone to use it even in ClosedSource projects as long as the conditions of the license are met.

The DLL as it is provided for download from
http://assarbad.info/stuff/MACkerer2.rar
was running for more than 2 years in its current form on Windows 2000 Server and Windows 2003 Server and has proven its reliability. The method was, as I pointed out, implemented earlier in a Delphi DLL and is approx. 1 year older than the version of the DLL offered.

Have fun with MACkerer2 ... and spread the word!

// Oliver

gimp Milan

gimp Milan — Tue, 19 Dec 2006 07:41:01 GMT

Ah now for the best part. I had always wanted to test this callout API thing. This is perhaps the most powerful way to leverage your Windows DHCP server. With the DHCP server callout, in a way, the whole DHCP server source code is before you for you to change and fine tune to your specific needs. In reality you really don't get the source code access but you do get all the power you would get had you really had the source code access. This is perhaps the best way to encourage people to build upon and extend your software's capability while still staying in the commercial realm and without throwing open the product's source code. I won't discuss the nitty-gritties of this callout technique as it has been properly documented here: DHCP Server callout API.

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re: All about the DHCP server callout API functions.

Phill Bowden — Thu, 03 May 2007 17:12:28 GMT

Great post. The MSDN documentation on this stuff is ok, but it contains a flaw in not telling us that the registry value required is "CalloutDlls". Without that info no-one is going to be able to use this stuff, and this is the only place I was able to find it.

re: All about the DHCP server callout API functions.

Marc Thomas — Tue, 07 Aug 2007 12:58:24 GMT

Has anyone managed to use DHCPPacketSendHook or DhcpNewPktHook to modify the packet and add more options for example. I understand the API reasonably well, however it isn't obvious how to handle memory allocation/freeing etc when extending the packet. Has anyone done this?

I do not think so

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re: All about the DHCP server callout API functions.

Son Vuong Kim — Sun, 30 Dec 2007 14:41:57 GMT

Hi,

The good work. I am researching DHCP for detect new computer when plug in LAN, so You could share your code to me .

Thanks very much

Regards,

re: All about the DHCP server callout API functions.

Son Vuong Kim — Sun, 30 Dec 2007 14:43:48 GMT

My email: vuongkimson@gmail.com

re: All about the DHCP server callout API functions.

Dave — Wed, 26 Mar 2008 18:43:26 GMT

Is there a way not to allow the dhcp server to assign an IP to a machine until you make a reservation for the machine, without using the call out api?

for example, on a Linux machine, you can configure the Linux DHCP server with option "ignore unknown-clients" to forbid the server assign IPs to unknown machines.

Thank

Dave

Concesi?n direcciones por DHCP | hilpers

Concesi?n direcciones por DHCP | hilpers — Tue, 20 Jan 2009 22:18:49 GMT

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