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packetdrill

This is the official Google release of packetdrill.

The packetdrill scripting tool enables quick, precise tests for entire TCP/UDP/IPv4/IPv6 network stacks, from the system call layer down to the NIC hardware. packetdrill currently works on Linux, FreeBSD, OpenBSD, and NetBSD. It can test network stack behavior over physical NICs on a LAN, or on a single machine using a tun virtual network device.

The code is GPLv2. Currently the source for the testing tool and a number of test scripts is in the git repository. We will continue to post more tests from our team's Linux TCP test suite (described in our USENIX paper), as time permits.

Links:

External links:

How To Get Started with packetdrill

First, download the dependencies that you will need in order to build and run packetdrill. If you are on a Linux system based on Debian/Ubuntu then you can use a command like:

sudo apt install git gcc make bison flex python net-tools

To check out and build packetdrill:

git clone https://github.com/google/packetdrill.git
cd packetdrill/gtests/net/packetdrill
./configure
make

How To Run All Local Tests for Linux

If you are on a machine with a recent Linux kernel you can su to root and run all of the TCP stack tests included in the packetdrill distribution in the tcp/ directory:

cd ..
./packetdrill/run_all.py -S -v -L -l tcp/

packetdrill's Design

Execution Model

packetdrill parses an entire test script, and then executes each timestamped line in real time -- at the pace described by the timestamps -- to replay and verify the scenario. The packetdrill interpreter has one thread for the main flow of events and another for executing any system calls that the script expects to block (e.g., poll()).

For convenience, scripts use an abstracted notation for packets. Internally, packetdrill models aspects of TCP and UDP behavior; to do this, packetdrill maintains mappings to translate between the values in the script and those in the live packet. The translation includes IP, UDP, and TCP header fields, including TCP options such as SACK and timestamps. Thus packetdrill tracks each socket and its IP addresses, port numbers, TCP sequence numbers, and TCP timestamps.

Local and Remote Testing

packetdrill enables two modes of testing: local mode, using a TUN virtual network device, or remote mode, using a physical NIC.

In local mode, packetdrill uses a single machine and a TUN virtual network device as a source and sink for packets. This tests the system call, sockets, TCP, and IP layers, and is easier to use because there is less timing variation, and users need not coordinate access to multiple machines.

In remote mode, users run two packetdrill processes, one of which is on a remote machine and speaks to the system under test over a LAN. This approach tests the full networking system: system calls, sockets, TCP, IP, software and hardware offload mechanisms, the NIC driver, NIC hardware, wire, and switch; however, due to the inherent variability in the many components under test, remote mode can result in larger timing variations, which can cause spurious test failures.

The packet plumbing is, naturally, a bit different in local and remote modes. To capture outgoing packets packetdrill uses a packet socket (on Linux) or libpcap (on BSD-derived OSes). To inject packets locally packetdrill uses a TUN device; to inject packets over the physical network in remote mode packetdrill again uses a packet socket or libpcap. To consume test packets in local mode packetdrill uses a TUN device; remotely, packets go over the physical network and packetdrill sets up filtering rules to drop the packets before layer 4 (UDP or TCP) processing in the remote kernel sees them.

Local Mode

Local mode is the default, so to use it you need no special command line flags; you only need to provide the path of the script to execute:

./packetdrill foo.pkt

Remote Mode

To use remote mode, on the machine under test (the "client" machine), specify the --wire_server_at option to specify the DNS name or IP address of the remote server machine to which the client packetdrill instance will connect. Only the client instance takes a packetdrill script argument, which can be the path of any ordinary packetdrill test script:

client# ./packetdrill --wire_server_at=<server_name_or_ip> foo.pkt

On the remote machine, run the following to have a packetdrill process act as a "wire server" daemon to inject and sniff packets remotely on the wire:

server# ./packetdrill --wire_server

How does this work? First, the client packetdrill instance connects to the server packetdrill instance (using TCP), and sends the command line options and the contents of the script file to the server instance. Then the client and server packetdrill instances work in concert to execute the script and test the client machine's network stack.

IP Addresses for packetdrill Tests

Remote or local mode tests may optionally specify arbitrary IP addresses to use for the test traffic, using the following command line arguments:

--local_ip=<local_ip_addr>     # test traffic address for machine under test
--netmask_ip=<netmask_ip>      # test traffic netmask (if testing IPv4)
--gateway_ip=<gateway_ip_addr> # test traffic address for gateway
--remote_ip=<remote_ip_addr>   # test traffic address for remote endpoint

By default, remote mode tests use the "primary" IP address of the client and server machines for the test traffic (where the "primary" address is the IP address to which the hostname resolves). With this configuration, the client and server can be anywhere in the same layer-3 routable domain (though it is highly recommended to only use packetrill in an internal RFC 1918 IP address space, for "lab" testing, rather than in the public Internet).

When a remote mode test uses arbitrary IP addresses, the packetdrill client and server processes must be on the same layer 2 broadcast domain (e.g., on the same Ethernet switch), so that the server machine may act as a gateway to reach the remote IP address configured via the --remote_ip command line argument.

How To Submit a Patch for packetdrill

We welcome patches with bug fixes or new features for packetdrill. The packetdrill project uses git for source code management. Please follow the following steps when sending in a patch for packetdrill:

  1. join the packetdrill e-mail list, so your e-mails to the list will be accepted by Google groups
  2. edit some files, compile, test
  3. verify that you can certify the origin of this code with a Signed-off-by footer, according to the standards of the Linux open source project
  4. git commit your change with a message like:
packetdrill: add amazing feature foo

This commit adds amazing feature foo, which ...

Tested on FooOS and BarOS by doing the following:
 ...

Signed-off-by: John Doe <[email protected]>
  1. Generate git patches using: git format-patch HEAD~1
  2. Check style for the patches by running checkpatch.pl from the Linux source tree, e.g.:
wget http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/scripts/checkpatch.pl
chmod u+x checkpatch.pl
./checkpatch.pl --no-tree --ignore FSF_MAILING_ADDRESS 00*.patch
  1. You can submit your patch as either a GitHub pull request or an e-mail patch series, with something like:
git send-email --to [email protected] 00*.patch