10. DPDK packet capture libraries and tools
This document describes how the Data Plane Development Kit (DPDK) Packet Capture Framework is used for capturing packets on DPDK ports. It is intended for users of DPDK who want to know more about the Packet Capture feature and for those who want to monitor traffic on DPDK-controlled devices.
The DPDK packet capture framework was introduced in DPDK v16.07
and enhanced in 21.11.
The DPDK packet capture framework consists of the libraries
for collecting packets librte_pdump
and writing packets to a file librte_pcapng
.
There are two sample applications: dpdk-dumpcap
and older dpdk-pdump
.
10.1. Introduction
The librte_pdump library provides the API required to allow users to initialize the packet capture framework and to enable or disable packet capture. The library works on a multi-process communication model and its usage is recommended for debugging purposes.
The librte_pcapng library provides the API to format packets and write them to a file in Pcapng format.
The dpdk-dumpcap is a tool that captures packets in
like Wireshark dumpcap does for Linux.
It runs as a DPDK secondary process and captures packets
from one or more interfaces and writes them to a file in Pcapng format.
The dpdk-dumpcap
tool is designed to take
most of the same options as the Wireshark dumpcap
command.
Without any options it will use the packet capture framework to capture traffic from the first available DPDK port.
The dpdk-testpmd
application can be used to initialize
the packet capture framework and acts as a server,
and the dpdk-dumpcap
tool acts as a client.
To view Rx or Tx packets of dpdk-testpmd
,
the application should be launched first,
and then the dpdk-dumpcap
tool.
Packets from dpdk-testpmd
will be sent to the tool,
and then to the Pcapng file.
Some things to note:
- All tools using
librte_pdump
can only be used in conjunction with a primary application which has the packet capture framework initialized already. In dpdk, onlytestpmd
is modified to initialize packet capture framework, other applications remain untouched. So, if thedpdk-dumpcap
tool has to be used with any application other than the testpmd, the user needs to explicitly modify that application to call the packet capture framework initialization code. Refer to theapp/test-pmd/testpmd.c
code and look forpdump
keyword to see how this is done. - The
dpdk-pdump
tool is an older tool created as demonstration oflibrte_pdump
library. Thedpdk-pdump
tool provides more limited functionality and depends on the Pcap PMD. It is retained only for compatibility reasons; users should usedpdk-dumpcap
instead.
10.2. Test Environment
The overview of using the Packet Capture Framework and the dpdk-dumpcap
utility
for packet capturing on the DPDK port in
Fig. 10.15.
10.3. Running the Application
The following steps demonstrate how to run the dpdk-dumpcap
tool to capture
Rx side packets on dpdk_port0 in Fig. 10.15 and
inspect them using tcpdump
.
Launch testpmd as the primary application:
sudo <build_dir>/app/dpdk-testpmd -c 0xf0 -n 4 -- -i --port-topology=chained
Launch the dpdk-dumpcap as follows:
sudo <build_dir>/app/dpdk-dumpcap -w /tmp/capture.pcapng
Send traffic to dpdk_port0 from traffic generator. Inspect packets captured in the file capture.pcapng using a tool such as tcpdump or tshark that can interpret Pcapng files:
$ tcpdump -nr /tmp/capture.pcapng reading from file /tmp/capture.pcap, link-type EN10MB (Ethernet) 11:11:36.891404 IP 4.4.4.4.whois++ > 3.3.3.3.whois++: UDP, length 18 11:11:36.891442 IP 4.4.4.4.whois++ > 3.3.3.3.whois++: UDP, length 18 11:11:36.891445 IP 4.4.4.4.whois++ > 3.3.3.3.whois++: UDP, length 18