[Winpcap-users] On win32, how to increase kernel buffer size more than 128

LeeGilbert gilgil1973 at hotmail.com
Fri Nov 20 10:40:14 PST 2009

Hi, I am Gilbert Lee.
while (true){  capture packet; // (1)  process packet; // (2)}
While you process the packet, if you would save VoIP traffic packets into audio files such as WAV or MP3,there might be some cases of process load.For example, CPU(RTP processing, audio codec decoding), disk(writing into file), or any other I/O activities.It is important for application to avoid accumulating delay of processing packet time(2).Neither kernel buffer size nor NIC card specification are not the problem.

From: gianluca.varenni at cacetech.com
To: winpcap-users at winpcap.org
Date: Fri, 20 Nov 2009 10:05:00 -0800
Subject: Re: [Winpcap-users] On win32,	how to increase kernel buffer size more than 128

128MB is basically a hard limit of 
the windows kernel on 32 bit machines (it's actually a bit higher than that). 
There is nothing you can do to change it. 
However, let's step back for 
one second. Increasing the kernel buffer size helps only in some very limited 
situations i.e. when you average traffic rate is pretty low, you have some short 
term spikes of traffic, and your application is not able to cope with these 
sudden spikes in a timely fashion. Increasing the kernel buffer size will help 
because the packets of the spike will be stored in the buffer while your 
application slowly processes them. It's my understanding that in your case you 
average traffic rate is just higher (250Mbps). In this case, increasing the 
kernel buffer size will not help. It will just delay the instant when you will 
start dropping packets (e.g. after 10 seconds from the beginning of the capture 
instead of 1second). In this case you need to understand why you are losing 
- is your application too slow 
to process the packets?
- are you dumping to disk? In 
this case, the disk can definitely be a bottleneck.
Hope it 

  ----- Original Message ----- 
  To: winpcap-users at winpcap.org 
  Sent: Friday, November 20, 2009 7:54 
  Subject: [Winpcap-users] On win32,how to 
  increase kernel buffer size more than 128

  My machine windows XP (win32) gets 
  the voice traffic of more than 250 Mbps at NIC from a switch. Basically, my 
  NIC was at 100 Mbps and the port on the switch is also the same. I am 
  developing an app to use winpcap lib to read packets from my NIC and write it 
  to file. I also ran parallel wireshark to check performance of my app. When my 
  app and wireshark running both at a time on my machine, I could clearly see 
  that the packets were getting lost. This was at the time when the traffic was 
  100 Mbps. When my app was trying to read 100 Mbps packets rate I could clearly 
  see that not all the packets were read and most of the packets were lost by my 
  app but in wireshark I could see all the packets in sequence, thought the 
  limit of 100 Mbps is reached, I increased the link to be 1Gig at switch port 
  and my NIC. Now the 100 Mbps is ok. 
  I increased the load to receive 
  150 Mbps, which almost was very equal to the wireshark capturing, was fine 
  there. When I jumped to 200 Mbps and (max) 250 Mbps traffic. 
  Here I again encountered the 
  packets are getting lost. Now this time when I compared with wireshark, there 
  I could see clearly that it did not had some of the sequence packets and it 
  did not mention or say that the packet segmentation lost. 
  Might be that the packets are 
  genuinely lost at the switch or the winpcap library kernel buffer is getting 
  overflown at this limit. At the switch the port is 1Gig bit, seems like no 
  issue from the switch port. Found that the winpcap has limit of 128 MB kernel 
  buffer size in the 32 bit. I ran the same in the 64 bit machine, got the same 
  issue there also. But its limit there seems to be 128 GB. Not sure whether 
  these values are correct or not. 
  My next alternate is to try 
  increasing the winpcap kernel buffer size for 32 bit. I don’t want to try new 
  things with 64 bit machine. I saw some thread to use 
  AdapterObject, int dim) function.
  But where I can I find complete 
  details of where can I find this function in which file of Winpcap file and 
  details of the library name, file name, dll name. FYI, my app uses v4.0.2 
  winpcap. A quick response with some helpful stuff is 

Winpcap-users at winpcap.org
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