PacketGenerator
This project provides a simple packet generator and capture tool. It is designed for use by anyone who wants to inject packets into a network and/or observe packets exiting a network.
The generation feature in the current implementation is a "playback" mechanism—a sequence of Ethernet frames is loaded from a PCAP dump file into the generator which then proceeds to transmit that sequence of frames. Delay between individual frames can be tightly controlled; by default the generator will use the delay specified in the pcap source file. A user can optionally specify a maximum data rate and/or a set delay between frames.
The packet generator also be used to report statistics on packets exiting the network and optionally to record the packets exiting the network. These feature are useful for analyzing throughput through a device and for analyzing whether the data exiting a network is correct.
- Status :
- Current version :
- NetFPGA package requirement :
- Authors :
- Release date :
- Replay timing accuracy :
- Capture timestamp precision :
- Capture timestamp accuracy :
See Packet generator revision history for the revision history and to download older versions.
WARNING: The yum package is not yet available for 1.1.1.
- Install the [Guide#Install_NetFPGA_Base_Package]
- Install the packet generator
yum install netfpga-packet_generator
Download from here: netfpga_packet_generator_1_1_1.tar.gz
WARNING: Standalone package not currently available for 1.1.1. Run the following command:
packet_generator_setup.pl
- Ensure that the NetFPGA kernel driver is loaded and that the CPCI has been reprogrammed.
- Download the packet generator bitfile:
nf_download packet_generator.bit
The generator is controlled via the packet_generator.pl command:
packet_generator.pl
-q
[-r ] (Kbps)
[-i ]
[-d ] (ns)
[-c ]
[--pad]
[--nodrop]
[--wait]
[--ns]
Note: queue number should be a number between 0 and 3 inclusive, corresponding to nf2c0 through nf2c3.
- -q<queue number> <pcap file> : Specify the pcap file to load in and send from a queue
- -r<queue number> <rate> : Specify the rate for each queue in Kbps
- -i<queue number> <number of iterations> : Specify the number of iterations per queue
- -d<queue number> <delay between packets> : Specify the delay between packets in ns. If not specified then the delay recorded in the pcap file is used. A value of 0 will disable the delay.
- -c<queue number> <capture file> : Specify the capture file.
- --pad : Shorten all packets to 64 bytes maximum and allow the NetFPGA to pad the packets when sending them.
- --nodrop : Don't drop packets on input ports for which we're not capturing
- --wait : Wait for USR1 signal; helps with synchronizing multiple generators.
- --ns : Report times with nanosecond precision (default in microsecond). Stanard PCAP format only supports microsecond resolution -- nanosecond resolution is provided by multiplying all packet times by 1000. Thus, 1000s in the PCAP file corresponds to 1s realtime.
The example below is the output produced when sending data out port 2 (with port 2 linked directly to port 3). In this example the rate is limited to 1.000 Mbps:
Limiting MAC Queue 2 to 1.000 Mbps (tokens = 1, clks = 1000) Loaded 1 packet(s) into MAC Queue 2 Limiting CPU Queue 0 to 200.000 Mbps (tokens = 1, clks = 5) Limiting CPU Queue 1 to 200.000 Mbps (tokens = 1, clks = 5) Limiting CPU Queue 2 to 200.000 Mbps (tokens = 1, clks = 5) Limiting CPU Queue 3 to 200.000 Mbps (tokens = 1, clks = 5) Sending packets... Last packet scheduled for transmission at 0.512 seconds 0 seconds elapsed... Transmit statistics: '''<tt>================</tt>''' MAC Queue 2: Packets: 1000 Completed iterations: 1000 Receive statistics: '''<tt>===============</tt>''' MAC Queue 0: Packets: 0 MAC Queue 1: Packets: 0 MAC Queue 2: Packets: 0 MAC Queue 3: Packets: 1000 Bytes: 64000 Time: 0.511488512 s Rate: 1.001 Mbps (packet data only) Rate: 1.314 Mbps (including preamble/inter-packet gap)The output shows that the last packet is estimated to be transmitted at time 0.512 seconds. The transmit statistics for queue 2 indicate that 1000 packets were sent and 1000 iterations were completed. The receive statistics for MAC queue 3 (nf2c3) indicate that 1000 packets were received which totaled 64000 bytes. (In this example each packet was 64 bytes.) The time between the reception of the first byte to the reception of the last byte was approximately 0.511 s. This corresponds to a rate of 1.001 Mbps (or 1.314 Mbps if you include the preamble/inter-packet gap in the rate calculation).
Send the packets contained in the file http.pcap out nf2c0:
packet_generator.pl -q0 http.pcap
Send 10 iterations of the packets contained in http.pcap out nf2c0. Capture the data coming back in port nf2c1 into a file named nf2c1.pcap:
packet_generator.pl -q0 http.pcap -i0 10 -c1 nf2c1.pcap
Send the packets contained in http.pcap out nf2c0. Limit the rate to 1 Mbps (1000 Kbps):
packet_generator.pl -q0 http.pcap -r0 1000
Send the packets contained in http.pcap out nf2c0. Set the delay between packets to 0 ns:
packet_generator.pl -q0 http.pcap -d0 0
Send the packets contained in http0.pcap, http1.pcap, udp2.pcap, and udp3.pcap out interfaces nf2c0, nf2c1, nf2c2 and nf2c3 respectively. Capture the data coming back on all four ports to files nf1c0.pcap, nf2c1.pcap, nf2c2.pcap and nf2c3.pcap:
packet_generator.pl -q0 http0.pcap -q1 http1.pcap -q2 udp2.pcap -q3 udp3.pcap -c0 nf2c0.pcap -c1 nf2c1.pcap -c2 nf2c2.pcap -c3 nf2c3.pcap
Send the packets contained in http.pcap out nf2c0. Only load the headers of the packets into SRAM in the NetFPGA.
packet_generator.pl -q0 http.pcap --pad
Delay through a switch or router can be measured using the packet generator. Delay is measured using all four ports simultaneously: two ports are connected directly to one another and used to provide a "baseline" measurement, the other two are connected to the device under test and are used to measure the difference from the baseline.
For example, ports nf2c0 and nf2c1 are directly connected and ports nf2c2 and nf2c3 are connected to the device under test. The same packet stream is sent out nf2c0 and nf2c2 and the packets are captured on nf2c1 and nf2c3; the difference in receive times between nf2c1 and nf2c3 is the delay through the device under test.
packet_generator.pl -q0 test_pkts.pcap -c1 reference.pcap -q2 test_pkts.pcap -c3 device_test.pcap --ns
Note: The program used to display the pcap file must display absolute times to allow the comparison between the two receive ports. The difference in absolute time is the delay through the device under test. Some programs show times relative to the first packet by default. The following table lists some popular programs that read pcap files and how to display absolute times.
| Program | Default time format | How to display absolute times |
| tcpdump | absolute | N/A |
| wireshark | relative to first packet | Select View -> Time Display Format -> Time of Day |
| tshark | relative to first packet | Specify "-t a" on the command line |
Timestamping of received packets is performed in hardware. This allows packets to be timestamped with the accuracy of the clock on the NetFPGA board. (The accuracy of timestamps produced by software tools such as tcpdump is significantly less since each packet must be transferred from hardware to software. The process of notifying the kernel of an available packet and then transferring that packet into the kernel introduces a (small) variable delay thus limiting the accuracy of timestamps reported by tcpdump .)
Timestamps in the output pcap file can be recorded with millisecond (default) or nanosecond precision. Timestamps recorded with nanosecond precision are multiplied by 1000, thus a time of 1000s in the output file represents 1s in hardware. This is done because the standard pcap file format only supports millisecond resolution. (A variant of the pcap file format does support nanosecond resoultion however this is not compatible with all programs.)
Note that timestamps recorded in the captured pcap file are based upon the hardware timestamp.
All measurements are performed in hardware. The packet counter is 32 bits and the byte counter is 40 bits. The time reported during a measurement is reported with nanosecond precision—this is only as accurate as the clock on the NetFPGA. The time reported is the time from the beginning of the first bit of data to the end of the last bit of data received—the preamble before the first packet is not included.
An example of a measurement on MAC queue 3 (nf2c3) is:
MAC Queue 3:
Packets: 1000
Bytes: 1518000
Time: 12.131868144 s
Rate: 1.001 Mbps
The hardware attempts to send all packets received (on the relevant ports) to software for processing when performing packet capture. Since the PCI bandwidth is less than the maximum combined receive bandwidth across all four Ethernet ports it is possible that received packets will be dropped. Dropping of packets occurs when the buffers on the NetFPGA board overflow.
The measurement statistics are correct regardless of whether packet are dropped.
Many programs have the ability to generate pcap files. Two such programs are tcpdump and Wireshark.