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pIpHeader = (iphdr_ptr)(pPacketBuffer->m_IBuffer + ETHER_HEADER_LENGTH);
pTcpHeader = (tcphdr_ptr)(((PUCHAR)pIpHeader) + sizeof(DWORD)*pIpHeader->ip_hl);pIPHeader = (iphdr*)PacketBuffer.m_IBuffer+14;
Typecasting has a higher priority than operator + above. You have to change it to:
pIPHeader = (iphdr*)PacketBuffer.m_IBuffer[14];
or
pIPHeader = (iphdr*)(PacketBuffer.m_IBuffer+14);
Can I limit bandwidth using winpkfltr for each ip/source combination?
Yes
If so, Please give me some directions on how to do this?
The basic idea is pretty simple. One possible realization is the following. Create a queue and put all packets into. Also create a periodic timer and each time when timer fires calculate time passed since last timer. Then claculate the amount of data you can allow to pass for the given time and process as many packets from the queue as it fits into clculated amount of data.
Can I use Winpkfltr to look at the ip header and make a decision on to drop/forward the packet?
Yes. You can take PassThru sample as a base. If you decide to drop the packet just don’t reinject it into the stack (by calling SendPacketToAdapter or SendPacketToMstcp).
This function should be able to drop or forward the packet based on some criteria. But here is the problem:
I dont want to drop all packets going to certain ip and port. For the same ip and port, I only want to drop say 10% of the packets and for some other ip/port, drop 20% of the packets.You can use kind of random generator, like C run time rand() routine.
An example, 20% chance of drop may look like:
if (rand() < RAND_MAX/5) bDrop = TRUE;I am trying to compile PAssThru in cbuilder folder.
I use:
bcc32.exe PassThru.cppHmm, I would start Borland C++ Builder, select File->Open Project, browse to PassThru.bpr and open it. After this I would click Project->Build PassThru.
it gives me many unrsolved external sybol errors. I understand that these are caused by the linker and I probably have to link it with ndisapi.dll, but I dont know how to do this.
Actually, you have to link to ndisapi.lib (stub library for ndisapi.dll).
As it is stated on VirtNet page it is just dummy network interface which does not do anything special itself (similar to MS loopback adapter, but supports all Windows operating systems). However, when used in combination with WinpkFilter you can build various virtual network environments over it.
WinpkFilter can be used for implementing two major tasks:
1) To indicate packets from the name of VirtNet to TCP/IP stack.
2) To intercept packets sent by TCP/IP stack to VirtNet network interface.You can create pure virtual network environment or bridge it to the real network or …. Actually, it depends only from you requirements.
So, Net firewall is full functional also if no one is logged on the system.
It’s right?Right
How can I see log of Firewall activity before I log on?
Log is not collected if firewall console (MMC snap-in) is not loaded, so in the current version there is no way to look through packets processed before logon.
NTKernelService stats dirung system start up, load latest firewall configuration into the driver and exits. So the situation you have expirienced is normal, this service should not be running, all the packet filtering functionality implemented in the kernel mode driver. Service is only responsible for configuring it.
If I add a rule allowing external access to one of those IP’s, all the others get accessable too. Why is that?
It should not be, probably the rule you create is too common and covers more than one IP.
Could someone please list a standard ruleset for allowing all traffic to port 80 on the server only. I know it’s very basic but it would be great to make sure I did it right.
Allow, TCP, Source IP: Any, Source Port: Any, Destination IP:[IP address your WWW server is bound to], Destination Port:80 Bidirectional.
Also set the security level to high.
I found a few bugs playing about. Are you interested in fixing then if i detail the issues?
Sure, if you find any bugs we would appreciate reporting about…
Do you also properly adjust DNS records length? (See dnsr_rdlength in the dns_record structure on the following link http://www.chiark.greenend.org.uk/ucgi/~richardk/cvsweb/dns/dns.h?rev=1.8&content-type=text/x-cvsweb-markup)
When I ‘overwrite’ the dns packet, can I do this within the already allocated buffer (by winpkfilter) OR do I need to create a totally new buffer. If so I do not have a clue how …. do you have an example ?
You can do this in the already allocated buffer. Actually, packet buffer is allocated by you, passed to WinpkFilter, which copies packet data into it and returns buffer to you. You can do anything with the packet but don’t forget to adjust packet length and recalculate requred checksums (UDP and IP in case of DNS).
As for the sample, Internet Gateway makes DNS redirect, it may help a bit. However, it does not modify DNS data, only packet header.
In case of DNS hijacking the easiest way is changing IP in the DSN response packet. You are right here.
In case of DNS you can form a new packet and replace the original one with it. It’s pretty easy to do because DNS works over UDP. However, the same trick with TCP packet is much more complex. Packets in TCP stream has sequence and aknowledgement numbers which are incremented to the amount of data payload in the packet. So if you change data length you must also track changes in SEQ and ACK fileds.
Well, yes it looks that Sygate is a problem. Their NDIS driver makes a dirty hook by modifying TCPIP.SYS module image (ArpSend routine if I remember fine). The only possible work around I could find is re-patching TCPIP.SYS after Sygate driver, but I really don’t like this solution. You can try to explain Sygate that dirty hacking is no good but I don’t think they would listen.
Latest WinpkFilter release also includes NDIS IM variant of WinpkFilter driver. Basically it was created to be used for Windows x64 (patching system is hardly possible there unless patching KeBugCheckEx in the kernel or something of this kind, see the notes from MS here http://www.microsoft.com/whdc/driver/kernel/64bitPatching.mspx). However, you can also use this driver for the latest operating systems (Windows 2000/XP/2003). By design it can coexists with Sygate driver, so it’s also a variant.
Internet Gateway 1.0 released. This is the first sample (even more than sample, it can be successfully used in the real environment) from the Advanced WinpkFilter Samples series which is targeted to demonstrate WInpkFilter libraries applicability. The source code for Internet Gateway is available to all registered WinpkFilter customers.
WinpkFilter 3.0.1 released. This service release includes:
1. Few improvements/bugfixes in legacy Windows 9x/ME driver.
2. Slightly changed driver API structures. Please refer WinpkFilter online documentation for the details.
3. All sample applications and API DLL now include Visual Studio 2005 projects. This greatly simplifies development under Windows XP/2003 x64.If you are eligible for a free update, please send the following details to support@ntkernel.com to receive an update instruction:
1. Your order ID.
2. An approximate date of purchasing.
