[Winpcap-users] Using too many pcap_t handles causes errors?

Gianluca Varenni gianluca.varenni at cacetech.com
Fri Dec 5 17:05:50 GMT 2008

  ----- Original Message ----- 
  From: Hakan Uluoz 
  To: winpcap-users at winpcap.org 
  Sent: Monday, December 01, 2008 6:16 AM
  Subject: [Winpcap-users] Using too many pcap_t handles causes errors?


  I am building a Win 32 application pair to monitor the SIP flow on a gateway. Basically the machine running the monitor applications is connected to a hub with the gateway. Main application monitors the SIP flow and runs sub-applications according to the SIP informations. Sub-applications monitor the RTP flows on forward and reverse directions. So all sub-applications have 2 pcap_t handles plus the main has 1. All have unique filters on the same adapter. Yes, the sub-applications are better be threads but there are some other restrictions irrelevant to wpcap that forces me to make them as applications.

  The machine runs on Win XP 32 bit with 2 GB of ram, with all unnecessary services removed. Applications run smooth on around 60 channels ( that makes 60*2 + 1 => 121 handles ). But when the channel count exceeds this boundry, findalldevs and open_live starts to fail. The errors are generally :

  Error in pcap_findalldevs: PacketGetAdapterNames: ERROR_INSUFFICIENT_BUFFER(122)

  Unable to open the adapter. <adapter> is not supported by WinPcap - errbuf :(NULL)

  Unable to open the adapter. <adapter> is not supported by WinPcap - errbuf : Cannot determine the network type(0)

  And mostly :
  Unable to open the adapter. <adapter> is not supported by WinPcap - errbuf : driver error: not enough memory to allocate the kernel buffer  
  First observations showed that when the total memory consumptions exceed 1GB errors start. Thought to be a paging issue and disabled paging but did not give a cure. As there is around 1 GB free physical ram available, I focussed on the kernel memory usage, and found that the errors start as soon as the non-paged kernel memory usage reaches around 256 MB ( which is the limit for all Win 32 versions AFAIK ). Besides the CPU usage is very acceptable under all circumstances.
  Can anyone clarify the reason for these errors I am getting? Is it memory, handle limitations? And I'd be thankful on suggestions on a solution. I already admit that everything has a limit but a way to tripple or double the channel count ( e.g. monitoring 180-120 channels ) would be quite useful.

The problem is non paged pool exaustion: every capture instance by default uses a 1MB kernel buffer that is allocated from the non paged pool, plus some kB for the internal structures (I don't remember exactly how many). 
Several solutions come to my mind:
- after you open the adapter with pcap_open_live, set the kernel buffer size to a smaller one (with pcap_setbuff).
- redesign your application so that you open less pcap_t handles and then dispatch the packets to different threads
- use a 64bit machine.

Have a nice day

  As a note I am using the WinPcap 4.0.2. 
  My best regards,


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  Winpcap-users at winpcap.org
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