# Revision history [back]

### Dumpcap/TCPDump packet loss when writing data to disk with high traffic

I'm using PyShark to capture packets on a relatively high traffic network. I noticed that packets were dropped in PyShark due to the high traffic.

Checking the PyShark code, it runs Dumpcap and pipes its output to TShark.

Running both manually with these commands results in about a 33% packet loss. (Testing with a tcpreplay of a pcap of 9786 packets in about 6 seconds).

 mkfifo /tmp/pipe 

 dumpcap -q -i lo -a duration:10 -w - > /tmp/pipe 

 tshark -l -n -T pdml -w out.pcap -r - < /tmp/pipe 

However, running Dumpcap by itself works perfectly fine with 0% packet loss.

 dumpcap -i lo -a duration:10 -w - 

I found two solutions that are not exactly ideal though

Solution 1

Edit the PyShark code to run TShark by itself to both capture and output its data for PyShark to process

Solution 2

Edit PyShark code to use Gulp to write more efficiently to the disk. However it seems that Gulp reaches its maximum buffer size in about 10 seconds on a high traffic test of about 5MB/s). I cannot find much documentation on how to increase its buffer size.

 mkfifo /tmp/pipe 

 dumpcap -q -i lo -a duration:10 -w - | gulp -c > /tmp/pipe 

 tshark -l -n -T pdml -w out.pcap -r - < /tmp/pipe 

Error:  gulp: ring buffer full