VPP Test Framework


The goal of the VPP Test Framework is to ease writing, running and debugging unit tests for the VPP. For this, python was chosen as a high level language allowing rapid development with scapy providing the necessary tool for creating and dissecting packets.

Anatomy of a test case

Python's unittest is used as the base framework upon which the VPP test framework is built. A test suite in the VPP Test Framework consists of multiple classes derived from VppTestCase, which is itself derived from TestCase. The test class defines one or more test functions, which act as test cases.

Function flow when running a test case is:

  1. setUpClass <VppTestCase.setUpClass>: This function is called once for each test class, allowing a one-time test setup to be executed. If this functions throws an exception, none of the test functions are executed.

  2. setUp <VppTestCase.setUp>: The setUp function runs before each of the test functions. If this function throws an exception other than AssertionError or SkipTest, then this is considered an error, not a test failure.

  3. test_<name>: This is the guts of the test case. It should execute the test scenario and use the various assert functions from the unittest framework to check necessary. Multiple test_<name> methods can exist in a test case.

  4. tearDown <VppTestCase.tearDown>: The tearDown function is called after each test function with the purpose of doing partial cleanup.

  5. tearDownClass <VppTestCase.tearDownClass>: Method called once after running all of the test functions to perform the final cleanup.


Each test case has a logger automatically created for it, stored in 'logger' property, based on logging. Use the logger's standard methods debug(), info(), error(), ... to emit log messages to the logger.

All the log messages go always into a log file in temporary directory (see below).

To control the messages printed to console, specify the V= parameter.

make test         # minimum verbosity
make test V=1     # moderate verbosity
make test V=2     # maximum verbosity

Parallel test execution

VPP Test Framework test suites can be run in parallel. Each test suite is executed in a separate process spawned by Python multiprocessing process.

The results from child test suites are sent to parent through pipes, which are aggregated and summarized at the end of the run.

Stdout, stderr and logs logged in child processes are redirected to individual parent managed queues. The data from these queues are then emitted to stdout of the parent process in the order the test suites have finished. In case there are no finished test suites (such as at the beginning of the run), the data from last started test suite are emitted in real time.

To enable parallel test run, specify the number of parallel processes:

make test TEST_JOBS=n       # at most n processes will be spawned
make test TEST_JOBS=auto    # chosen based on the number of cores
                            # and the size of shared memory

Test temporary directory and VPP life cycle

Test separation is achieved by separating the test files and vpp instances. Each test creates a temporary directory and it's name is used to create a shared memory prefix which is used to run a VPP instance. The temporary directory name contains the testcase class name for easy reference, so for testcase named 'TestVxlan' the directory could be named e.g. vpp-unittest-TestVxlan-UNUP3j. This way, there is no conflict between any other VPP instances running on the box and the test VPP. Any temporary files created by the test case are stored in this temporary test directory.

The test temporary directory holds the following interesting files:

  • log.txt - this contains the logger output on max verbosity

  • pg*_in.pcap - last injected packet stream into VPP, named after the interface, so for pg0, the file will be named pg0_in.pcap

  • pg*_out.pcap - last capture file created by VPP for interface, similarly, named after the interface, so for e.g. pg1, the file will be named pg1_out.pcap

  • history files - whenever the capture is restarted or a new stream is added, the existing files are rotated and renamed, so all the pcap files are always saved for later debugging if needed

  • core - if vpp dumps a core, it'll be stored in the temporary directory

  • vpp_stdout.txt - file containing output which vpp printed to stdout

  • vpp_stderr.txt - file containing output which vpp printed to stderr

NOTE: existing temporary directories named vpp-unittest-* are automatically removed when invoking 'make test*' or 'make retest*' to keep the temporary directory clean.

Virtual environment

Virtualenv is a python module which provides a means to create an environment containing the dependencies required by the VPP Test Framework, allowing a separation from any existing system-wide packages. VPP Test Framework's Makefile automatically creates a virtualenv inside build-root and installs the required packages in that environment. The environment is entered whenever executing a test via one of the make test targets.

Naming conventions

Most unit tests do some kind of packet manipulation - sending and receiving packets between VPP and virtual hosts connected to the VPP. Referring to the sides, addresses, etc. is always done as if looking from the VPP side, thus:

  • local_ prefix is used for the VPP side. So e.g. local_ip4 <VppInterface.local_ip4> address is the IPv4 address assigned to the VPP interface.

  • remote_ prefix is used for the virtual host side. So e.g. remote_mac <VppInterface.remote_mac> address is the MAC address assigned to the virtual host connected to the VPP.

Automatically generated addresses

To send packets, one needs to typically provide some addresses, otherwise the packets will be dropped. The interface objects in VPP Test Framework automatically provide addresses based on (typically) their indexes, which ensures there are no conflicts and eases debugging by making the addressing scheme consistent.

The developer of a test case typically doesn't need to work with the actual numbers, rather using the properties of the objects. The addresses typically come in two flavors: '<address>' and '<address>n' - note the 'n' suffix. The former address is a Python string, while the latter is translated using socket.inet_pton to raw format in network byte order - this format is suitable for passing as an argument to VPP APIs.

e.g. for the IPv4 address assigned to the VPP interface:

  • local_ip4 - Local IPv4 address on VPP interface (string)

  • local_ip4n - Local IPv4 address - raw, suitable as API parameter.

These addresses need to be configured in VPP to be usable using e.g. VppInterface.config_ip4 API. Please see the documentation to VppInterface for more details.

By default, there is one remote address of each kind created for L3: remote_ip4 and remote_ip6. If the test needs more addresses, because it's simulating more remote hosts, they can be generated using generate_remote_hosts API and the entries for them inserted into the ARP table using configure_ipv4_neighbors API.

Packet flow in the VPP Test Framework

Test framework -> VPP

VPP Test Framework doesn't send any packets to VPP directly. Traffic is instead injected using packet-generator interfaces, represented by the VppPGInterface class. Packets are written into a temporary .pcap file, which is then read by the VPP and the packets are injected into the VPP world.

To add a list of packets to an interface, call the VppPGInterface.add_stream method on that interface. Once everything is prepared, call pg_start method to start the packet generator on the VPP side.

VPP -> test framework

Similarly, VPP doesn't send any packets to VPP Test Framework directly. Instead, packet capture feature is used to capture and write traffic to a temporary .pcap file, which is then read and analyzed by the VPP Test Framework.

The following APIs are available to the test case for reading pcap files.

  • VppPGInterface.get_capture: this API is suitable for bulk & batch style of test, where a list of packets is prepared & sent, then the received packets are read and verified. The API needs the number of packets which are expected to be captured (ignoring filtered packets - see below) to know when the pcap file is completely written by the VPP. If using packet infos for verifying packets, then the counts of the packet infos can be automatically used by VppPGInterface.get_capture to get the proper count (in this case the default value None can be supplied as expected_count or omitted altogether).

  • VppPGInterface.wait_for_packet: this API is suitable for interactive style of test, e.g. when doing session management, three-way handshakes, etc. This API waits for and returns a single packet, keeping the capture file in place and remembering context. Repeated invocations return following packets (or raise Exception if timeout is reached) from the same capture file (= packets arriving on the same interface).

NOTE: it is not recommended to mix these APIs unless you understand how they work internally. None of these APIs rotate the pcap capture file, so calling e.g. VppPGInterface.get_capture after VppPGInterface.wait_for_packet will return already read packets. It is safe to switch from one API to another after calling VppPGInterface.enable_capture as that API rotates the capture file.

Automatic filtering of packets:

Both APIs (VppPGInterface.get_capture and VppPGInterface.wait_for_packet) by default filter the packet capture, removing known uninteresting packets from it - these are IPv6 Router Advertisements and IPv6 Router Alerts. These packets are unsolicited and from the point of VPP Test Framework are random. If a test wants to receive these packets, it should specify either None or a custom filtering function as the value to the 'filter_out_fn' argument.

Common API flow for sending/receiving packets:

We will describe a simple scenario, where packets are sent from pg0 to pg1 interface, assuming that the interfaces were created using create_pg_interfaces API.

  1. Create a list of packets for pg0:

    packet_count = 10
    packets = create_packets(src=self.pg0, dst=self.pg1,
  2. Add that list of packets to the source interface:

  3. Enable capture on the destination interface:

  4. Start the packet generator:

  5. Wait for capture file to appear and read it:

    capture = self.pg1.get_capture(expected_count=packet_count)
  6. Verify packets match sent packets:

    self.verify_capture(send=packets, captured=capture)

Test framework objects

The following objects provide VPP abstraction and provide a means to do common tasks easily in the test cases.

  • VppInterface: abstract class representing generic VPP interface and contains some common functionality, which is then used by derived classes

  • VppPGInterface: class representing VPP packet-generator interface. The interface is created/destroyed when the object is created/destroyed.

  • VppSubInterface: VPP sub-interface abstract class, containing common functionality for e.g. VppDot1QSubint and VppDot1ADSubint classes

How VPP APIs/CLIs are called

Vpp provides python bindings in a python module called vpp-papi, which the test framework installs in the virtual environment. A shim layer represented by the VppPapiProvider class is built on top of the vpp-papi, serving these purposes:

  1. Automatic return value checks: After each API is called, the return value is checked against the expected return value (by default 0, but can be overridden) and an exception is raised if the check fails.

  2. Automatic call of hooks:

    1. before_cli <Hook.before_cli> and before_api <Hook.before_api> hooks are used for debug logging and stepping through the test

    2. after_cli <Hook.after_cli> and after_api <Hook.after_api> hooks are used for monitoring the vpp process for crashes

  3. Simplification of API calls: Many of the VPP APIs take a lot of parameters and by providing sane defaults for these, the API is much easier to use in the common case and the code is more readable. E.g. ip_add_del_route API takes ~25 parameters, of which in the common case, only 3 are needed.

Utility methods

Some interesting utility methods are:

  • ppp: 'Pretty Print Packet' - returns a string containing the same output as Scapy's packet.show() would print

  • ppc: 'Pretty Print Capture' - returns a string containing printout of a capture (with configurable limit on the number of packets printed from it) using ppp

NOTE: Do not use Scapy's packet.show() in the tests, because it prints the output to stdout. All output should go to the logger associated with the test case.

Example: how to add a new test

In this example, we will describe how to add a new test case which tests basic IPv4 forwarding.

  1. Add a new file called test_ip4_fwd.py in the test directory, starting with a few imports:

    from framework import VppTestCase
    from scapy.layers.l2 import Ether
    from scapy.packet import Raw
    from scapy.layers.inet import IP, UDP
    from random import randint
  2. Create a class inherited from the VppTestCase:

    class IP4FwdTestCase(VppTestCase):
        """ IPv4 simple forwarding test case """
  3. Add a setUpClass function containing the setup needed for our test to run:

    def setUpClass(self):
        super(IP4FwdTestCase, self).setUpClass()
        self.create_pg_interfaces(range(2))  #  create pg0 and pg1
        for i in self.pg_interfaces:
            i.admin_up()  # put the interface up
            i.config_ip4()  # configure IPv4 address on the interface
            i.resolve_arp()  # resolve ARP, so that we know VPP MAC
  4. Create a helper method to create the packets to send:

    def create_stream(self, src_if, dst_if, count):
        packets = []
        for i in range(count):
            # create packet info stored in the test case instance
            info = self.create_packet_info(src_if, dst_if)
            # convert the info into packet payload
            payload = self.info_to_payload(info)
            # create the packet itself
            p = (Ether(dst=src_if.local_mac, src=src_if.remote_mac) /
                 IP(src=src_if.remote_ip4, dst=dst_if.remote_ip4) /
                 UDP(sport=randint(1000, 2000), dport=5678) /
            # store a copy of the packet in the packet info
            info.data = p.copy()
            # append the packet to the list
        # return the created packet list
        return packets
  5. Create a helper method to verify the capture:

    def verify_capture(self, src_if, dst_if, capture):
        packet_info = None
        for packet in capture:
                ip = packet[IP]
                udp = packet[UDP]
                # convert the payload to packet info object
                payload_info = self.payload_to_info(packet[Raw])
                # make sure the indexes match
                self.assert_equal(payload_info.src, src_if.sw_if_index,
                                  "source sw_if_index")
                self.assert_equal(payload_info.dst, dst_if.sw_if_index,
                                  "destination sw_if_index")
                packet_info = self.get_next_packet_info_for_interface2(
                # make sure we didn't run out of saved packets
                self.assert_equal(payload_info.index, packet_info.index,
                                  "packet info index")
                saved_packet = packet_info.data  # fetch the saved packet
                # assert the values match
                self.assert_equal(ip.src, saved_packet[IP].src,
                                  "IP source address")
                # ... more assertions here
                self.assert_equal(udp.sport, saved_packet[UDP].sport,
                                  "UDP source port")
                self.logger.error(ppp("Unexpected or invalid packet:",
        remaining_packet = self.get_next_packet_info_for_interface2(
                          "Interface %s: Packet expected from interface "
                          "%s didn't arrive" % (dst_if.name, src_if.name))
  6. Add the test code to test_basic function:

    def test_basic(self):
        count = 10
        # create the packet stream
        packets = self.create_stream(self.pg0, self.pg1, count)
        # add the stream to the source interface
        # enable capture on both interfaces
        # start the packet generator
        # get capture - the proper count of packets was saved by
        # create_packet_info() based on dst_if parameter
        capture = self.pg1.get_capture()
        # assert nothing captured on pg0 (always do this last, so that
        # some time has already passed since pg_start())
        # verify capture
        self.verify_capture(self.pg0, self.pg1, capture)
  7. Run the test by issuing 'make test' or, to run only this specific test, issue 'make test TEST=test_ip4_fwd'.