Topotests is a suite of topology tests for FRR built on top of micronet.

Installation and Setup

Topotests run under python3. Additionally, for ExaBGP (which is used in some of the BGP tests) an older python2 version (and the python2 version of pip) must be installed.

Tested with Ubuntu 20.04,Ubuntu 18.04, and Debian 11.

Instructions are the same for all setups (i.e. ExaBGP is only used for BGP tests).

Tshark is only required if you enable any packet captures on test runs.

Valgrind is only required if you enable valgrind on test runs.

Installing Topotest Requirements

apt-get install \
    gdb \
    iproute2 \
    net-tools \
    python3-pip \
    iputils-ping \
    tshark \
python3 -m pip install wheel
python3 -m pip install 'pytest>=6.2.4'
python3 -m pip install 'pytest-xdist>=2.3.0'
python3 -m pip install 'scapy>=2.4.5'
python3 -m pip install xmltodict
# Use python2 pip to install older ExaBGP
python2 -m pip install 'exabgp<4.0.0'
useradd -d /var/run/exabgp/ -s /bin/false exabgp

# To enable the gRPC topotest install:
python3 -m pip install grpcio grpcio-tools

Enable Coredumps

Optional, will give better output.

disable apport (which move core files)

Set enabled=0 in /etc/default/apport.

Next, update security limits by changing /etc/security/limits.conf to:

#<domain>      <type>  <item>         <value>
*               soft    core          unlimited
root            soft    core          unlimited
*               hard    core          unlimited
root            hard    core          unlimited

Reboot for options to take effect.

SNMP Utilities Installation

To run SNMP test you need to install SNMP utilities and MIBs. Unfortunately there are some errors in the upstream MIBS which need to be patched up. The following steps will get you there on Ubuntu 20.04.

apt install libsnmp-dev
apt install snmpd snmp
apt install snmp-mibs-downloader
wget -O /usr/share/snmp/mibs/iana/IANA-IPPM-METRICS-REGISTRY-MIB
wget -O /usr/share/snmp/mibs/ietf/SNMPv2-PDU
wget -O /usr/share/snmp/mibs/ietf/IPATM-IPMC-MIB
edit /etc/snmp/snmp.conf to look like this
# As the snmp packages come without MIB files due to license reasons, loading
# of MIBs is disabled by default. If you added the MIBs you can reenable
# loading them by commenting out the following line.
mibs +ALL

FRR Installation

FRR needs to be installed separately. It is assume to be configured like the standard Ubuntu Packages:

  • Binaries in /usr/lib/frr

  • State Directory /var/run/frr

  • Running under user frr, group frr

  • vtygroup: frrvty

  • config directory: /etc/frr

  • For FRR Packages, install the dbg package as well for coredump decoding

No FRR config needs to be done and no FRR daemons should be run ahead of the test. They are all started as part of the test.

Manual FRR build

If you prefer to manually build FRR, then use the following suggested config:

./configure \
    --prefix=/usr \
    --localstatedir=/var/run/frr \
    --sbindir=/usr/lib/frr \
    --sysconfdir=/etc/frr \
    --enable-vtysh \
    --enable-pimd \
    --enable-pim6d \
    --enable-sharpd \
    --enable-multipath=64 \
    --enable-user=frr \
    --enable-group=frr \
    --enable-vty-group=frrvty \
    --enable-snmp=agentx \

And create frr user and frrvty group as follows:

addgroup --system --gid 92 frr
addgroup --system --gid 85 frrvty
adduser --system --ingroup frr --home /var/run/frr/ \
   --gecos "FRRouting suite" --shell /bin/false frr
usermod -G frrvty frr

Executing Tests

Configure your sudo environment

Topotests must be run as root. Normally this will be accomplished through the use of the sudo command. In order for topotests to be able to open new windows (either XTerm or byobu/screen/tmux windows) certain environment variables must be passed through the sudo command. One way to do this is to specify the -E flag to sudo. This will carry over most if not all your environment variables include PATH. For example:

sudo -E python3 -m pytest -s -v

If you do not wish to use -E (e.g., to avoid sudo inheriting PATH) you can modify your /etc/sudoers config file to specifically pass the environment variables required by topotests. Add the following commands to your /etc/sudoers config file.

Defaults env_keep="TMUX"
Defaults env_keep+="TMUX_PANE"
Defaults env_keep+="STY"
Defaults env_keep+="DISPLAY"

If there was already an env_keep configuration there be sure to use the += rather than = on the first line above as well.

Execute all tests in distributed test mode

sudo -E pytest -s -v -nauto --dist=loadfile

The above command must be executed from inside the topotests directory.

All test_* scripts in subdirectories are detected and executed (unless disabled in pytest.ini file). Pytest will execute up to N tests in parallel where N is based on the number of cores on the host.

Analyze Test Results (

By default router and execution logs are saved in /tmp/topotests and an XML results file is saved in /tmp/topotests/topotests.xml. An analysis tool is provided to archive and analyze these results after the run completes.

After the test run completes one should pick an archive directory to store the results in and pass this value to On first execution the results are moved to that directory from /tmp/topotests. Subsequent runs of with the same args will use that directories contents for instead of copying any new results from /tmp. Below is an example of this which also shows the default behavior which is to display all failed and errored tests in the run.

~/frr/tests/topotests# ./ -Ar run-save

Here we see that 4 tests have failed. We can dig deeper by displaying the captured logs and errors. First let’s redisplay the results enumerated by adding the -E flag

~/frr/tests/topotests# ./ -Ar run-save -E
0 bgp_multiview_topo1/
1 ospf_basic_functionality/
2 bgp_gr_functionality_topo2/
3 bgp_multiview_topo1/

Now to look at the error message for a failed test we use -T N where N is the number of the test we are interested in along with --errmsg option.

~/frr/tests/topotests# ./ -Ar run-save -T0 --errmsg
bgp_multiview_topo1/ AssertionError: BGP did not converge:

  IPv4 Unicast Summary (VIEW 1):
  BGP router identifier, local AS number 100 vrf-id -1
  BGP table version 1
  RIB entries 1, using 184 bytes of memory
  Peers 3, using 2169 KiB of memory

  Neighbor        V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down State/PfxRcd   PfxSnt Desc      4      65001         0         0        0    0    0    never      Connect        0 N/A      4      65002         0         0        0    0    0    never      Connect        0 N/A      4      65005         0         0        0    0    0    never      Connect        0 N/A

  Total number of neighbors 3

 assert False

Now to look at the error text for a failed test we can use -T RANGES where RANGES can be a number (e.g., 5), a range (e.g., 0-10), or a comma separated list numbers and ranges (e.g., 5,10-20,30) of the test cases we are interested in along with --errtext option. In the example below we’ll select the first failed test case.

~/frr/tests/topotests# ./ -Ar run-save -T0 --errtext
bgp_multiview_topo1/ def test_bgp_converge():
        "Check for BGP converged on all peers and BGP views"

        global fatal_error
        global net
            # Bail out with error if a router fails to converge
            bgpStatus = net["r%s" % i].cmd('vtysh -c "show ip bgp view %s summary"' % view)
>           assert False, "BGP did not converge:\n%s" % bgpStatus
E           AssertionError: BGP did not converge:
E             IPv4 Unicast Summary (VIEW 1):
E             BGP router identifier, local AS number 100 vrf-id -1
E             Neighbor        V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down State/PfxRcd   PfxSnt Desc
E         4      65001         0         0        0    0    0    never      Connect        0 N/A
E         4      65002         0         0        0    0    0    never      Connect        0 N/A

To look at the full capture for a test including the stdout and stderr which includes full debug logs, use --full option, or specify a -T RANGES without specifying --errmsg or --errtext.

~/frr/tests/topotests# ./ -Ar run-save -T0
@classname: bgp_multiview_topo1.test_bgp_multiview_topo1
@name: test_bgp_converge
@time: 141.401
@message: AssertionError: BGP did not converge:
system-out: --------------------------------- Captured Log ---------------------------------
2021-08-09 02:55:06,581 DEBUG: lib.micronet_compat.topo: Topo(unnamed): Creating
2021-08-09 02:55:06,581 DEBUG: lib.micronet_compat.topo: Topo(unnamed): addHost r1
2021-08-09 02:57:16,932 DEBUG: topolog.r1: LinuxNamespace(r1): cmd_status("['/bin/bash', '-c', 'vtysh -c "show ip bgp view 1 summary" 2> /dev/null | grep ^[0-9] | grep -vP " 11\\s+(\\d+)"']", kwargs: {'encoding': 'utf-8', 'stdout': -1, 'stderr': -2, 'shell': False})
2021-08-09 02:57:22,290 DEBUG: topolog.r1: LinuxNamespace(r1): cmd_status("['/bin/bash', '-c', 'vtysh -c "show ip bgp view 1 summary" 2> /dev/null | grep ^[0-9] | grep -vP " 11\\s+(\\d+)"']", kwargs: {'encoding': 'utf-8', 'stdout': -1, 'stderr': -2, 'shell': False})
2021-08-09 02:57:27,636 DEBUG: topolog.r1: LinuxNamespace(r1): cmd_status("['/bin/bash', '-c', 'vtysh -c "show ip bgp view 1 summary"']", kwargs: {'encoding': 'utf-8', 'stdout': -1, 'stderr': -2, 'shell': False})
--------------------------------- Captured Out ---------------------------------
system-err: --------------------------------- Captured Err ---------------------------------

Filtered results

There are 4 types of test results, [e]rrored, [f]ailed, [p]assed, and [s]kipped. One can select the set of results to show with the -S or --select flags along with the letters for each type (i.e., -S efps would select all results). By default will use -S ef (i.e., [e]rrors and [f]ailures) unless the --search filter is given in which case the default is to search all results (i.e., -S efps).

One can find all results which contain a REGEXP. To filter results using a regular expression use the --search REGEXP option. In this case, by default, all result types will be searched for a match against the given REGEXP. If a test result output contains a match it is selected into the set of results to show.

An example of using --search would be to search all tests results for some log message, perhaps a warning or error.

Using XML Results File from CI actually only needs the topotests.xml file to run. This is very useful for analyzing a CI run failure where one only need download the topotests.xml artifact from the run and then pass that to with the -r or --results option.

For local runs if you wish to simply copy the topotests.xml file (leaving the log files where they are), you can pass the -a (or --save-xml) instead of the -A (or -save) options.

Analyze Results from a Container Run can also be used with docker or podman containers. Everything works exactly as with a host run except that you specify the name of the container, or the container-id, using the -C or --container option. will then use the results inside that containers /tmp/topotests directory. It will extract and save those results when you pass the -A or -a options just as withe host results.

Execute single test

cd test_to_be_run
sudo -E pytest ./

For example, and assuming you are inside the frr directory:

cd tests/topotests/bgp_l3vpn_to_bgp_vrf
sudo -E pytest ./

For further options, refer to pytest documentation.

Test will set exit code which can be used with git bisect.

For the simulated topology, see the description in the python file.

Running Topotests with AddressSanitizer

Topotests can be run with AddressSanitizer. It requires GCC 4.8 or newer. (Ubuntu 16.04 as suggested here is fine with GCC 5 as default). For more information on AddressSanitizer, see

The checks are done automatically in the library call of checkRouterRunning (ie at beginning of tests when there is a check for all daemons running). No changes or extra configuration for topotests is required beside compiling the suite with AddressSanitizer enabled.

If a daemon crashed, then the errorlog is checked for AddressSanitizer output. If found, then this is added with context (calling test) to /tmp/AddressSanitizer.txt in Markdown compatible format.

Compiling for GCC AddressSanitizer requires to use gcc as a linker as well (instead of ld). Here is a suggest way to compile frr with AddressSanitizer for master branch:

git clone
cd frr
./configure \
    --enable-address-sanitizer \
    --prefix=/usr/lib/frr --sysconfdir=/etc/frr \
    --localstatedir=/var/run/frr \
    --sbindir=/usr/lib/frr --bindir=/usr/lib/frr \
    --with-moduledir=/usr/lib/frr/modules \
    --enable-multipath=0 --enable-rtadv \
    --enable-tcp-zebra --enable-fpm --enable-pimd \
sudo make install
# Create symlink for vtysh, so topotest finds it in /usr/lib/frr
sudo ln -s /usr/lib/frr/vtysh /usr/bin/

and create frr user and frrvty group as shown above.

Debugging Topotest Failures

Install and run tests inside tmux or byobu for best results.

XTerm is also fully supported. GNU screen can be used in most situations; however, it does not work as well with launching vtysh or shell on error.

For the below debugging options which launch programs or CLIs, topotest should be run within tmux (or screen)_, as gdb, the shell or vtysh will be launched using that windowing program, otherwise xterm will be attempted to launch the given programs.

NOTE: you must run the topotest (pytest) such that your DISPLAY, STY or TMUX environment variables are carried over. You can do this by passing the -E flag to sudo or you can modify your /etc/sudoers config to automatically pass that environment variable through to the sudo environment.

Capturing Packets

One can view and capture packets on any of the networks or interfaces defined by the topotest by specifying the --pcap=NET|INTF|all[,NET|INTF,...] CLI option as shown in the examples below.

# Capture on all networks in isis_topo1 test
sudo -E pytest isis_topo1 --pcap=all

# Capture on `sw1` network
sudo -E pytest isis_topo1 --pcap=sw1

# Capture on `sw1` network and on interface `eth0` on router `r2`
sudo -E pytest isis_topo1 --pcap=sw1,r2:r2-eth0

For each capture a window is opened displaying a live summary of the captured packets. Additionally, the entire packet stream is captured in a pcap file in the tests log directory e.g.,:

$ sudo -E pytest isis_topo1 --pcap=sw1,r2:r2-eth0
$ ls -l /tmp/topotests/isis_topo1.test_isis_topo1/
-rw------- 1 root root 45172 Apr 19 05:30 capture-r2-r2-eth0.pcap
-rw------- 1 root root 48412 Apr 19 05:30 capture-sw1.pcap

Viewing Live Daemon Logs

One can live view daemon or the frr logs in separate windows using the --logd CLI option as shown below.

# View `ripd` logs on all routers in test
sudo -E pytest rip_allow_ecmp --logd=ripd

# View `ripd` logs on all routers and `mgmtd` log on `r1`
sudo -E pytest rip_allow_ecmp --logd=ripd --logd=mgmtd,r1

For each capture a window is opened displaying a live summary of the captured packets. Additionally, the entire packet stream is captured in a pcap file in the tests log directory e.g.,:

When using a unified log file frr.log one substitutes frr for the daemon name in the --logd CLI option, e.g.,

# View `frr` log on all routers in test
sudo -E pytest some_test_suite --logd=frr

Spawning Debugging CLI, vtysh or Shells on Routers on Test Failure

One can have a debugging CLI invoked on test failures by specifying the --cli-on-error CLI option as shown in the example below.

sudo -E pytest --cli-on-error all-protocol-startup

The debugging CLI can run shell or vtysh commands on any combination of routers It can also open shells or vtysh in their own windows for any combination of routers. This is usually the most useful option when debugging failures. Here is the help command from within a CLI launched on error:

test_bgp_multiview_topo1/test_bgp_routingTable> help

Basic Commands:
  cli   :: open a secondary CLI window
  help  :: this help
  hosts :: list hosts
  quit  :: quit the cli

  HOST can be a host or one of the following:
    - '*' for all hosts
    - '.' for the parent munet
    - a regex specified between '/' (e.g., '/rtr.*/')

New Window Commands:
  logd HOST [HOST ...] DAEMON   :: tail -f on the logfile of the given DAEMON for the given HOST[S]
  pcap NETWORK  :: capture packets from NETWORK into file capture-NETWORK.pcap the command is run within a new window which also shows packet summaries. NETWORK can also be an interface specified as HOST:INTF. To capture inside the host namespace.
  stderr HOST [HOST ...] DAEMON :: tail -f on the stderr of the given DAEMON for the given HOST[S]
  stdlog HOST [HOST ...]        :: tail -f on the `frr.log` for the given HOST[S]
  stdout HOST [HOST ...] DAEMON :: tail -f on the stdout of the given DAEMON for the given HOST[S]
  term HOST [HOST ...]  :: open terminal[s] (TMUX or XTerm) on HOST[S], * for all
  vtysh ROUTER [ROUTER ...]     ::
  xterm HOST [HOST ...] :: open XTerm[s] on HOST[S], * for all
Inline Commands:
  [ROUTER ...] COMMAND  :: execute vtysh COMMAND on the router[s]
  [HOST ...] sh <SHELL-COMMAND> :: execute <SHELL-COMMAND> on hosts

test_bgp_multiview_topo1/test_bgp_routingTable> r1 show int br
------ Host: r1 ------
Interface       Status  VRF             Addresses
---------       ------  ---             ---------
erspan0         down    default
gre0            down    default
gretap0         down    default
lo              up      default
r1-eth0         up      default
r1-stub         up      default


Additionally, one can have vtysh or a shell launched on all routers when a test fails. To launch the given process on each router after a test failure specify one of --shell-on-error or --vtysh-on-error.

Spawning vtysh or Shells on Routers

Topotest can automatically launch a shell or vtysh for any or all routers in a test. This is enabled by specifying 1 of 2 CLI arguments --shell or --vtysh. Both of these options can be set to a single router value, multiple comma-seperated values, or all.

When either of these options are specified topotest will pause after setup and each test to allow for inspection of the router state.

Here’s an example of launching vtysh on routers rt1 and rt2.

sudo -E pytest --vtysh=rt1,rt2 all-protocol-startup

Debugging with GDB

Topotest can automatically launch any daemon with gdb, possibly setting breakpoints for any test run. This is enabled by specifying 1 or 2 CLI arguments --gdb-routers and --gdb-daemons. Additionally --gdb-breakpoints can be used to automatically set breakpoints in the launched gdb processes.

Each of these options can be set to a single value, multiple comma-seperated values, or all. If --gdb-routers is empty but --gdb_daemons is set then the given daemons will be launched in gdb on all routers in the test. Likewise if --gdb_routers is set, but --gdb_daemons is empty then all daemons on the given routers will be launched in gdb.

Here’s an example of launching zebra and bgpd inside gdb on router r1 with a breakpoint set on nb_config_diff

sudo -E pytest --gdb-routers=r1 \
       --gdb-daemons=bgpd,zebra \
       --gdb-breakpoints=nb_config_diff \

Reporting Memleaks with FRR Memory Statistics

FRR reports all allocated FRR memory objects on exit to standard error. Topotest can be run to report such output as errors in order to check for memleaks in FRR memory allocations. Specifying the CLI argument --memleaks will enable reporting FRR-based memory allocations at exit as errors.

sudo -E pytest --memleaks all-protocol-startup

StdErr log from daemos after exit

When running with --memleaks, to enable the reporting of other, non-memory related, messages seen on StdErr after the daemons exit, the following env variable can be set:


(The value doesn’t matter at this time. The check is whether the env variable exists or not.) There is no pass/fail on this reporting; the Output will be reported to the console.

Collect Memory Leak Information

When running with --memleaks, FRR processes report unfreed memory allocations upon exit. To enable also reporting of memory leaks to a specific location, define an environment variable TOPOTESTS_CHECK_MEMLEAK with the file prefix, i.e.:

export TOPOTESTS_CHECK_MEMLEAK=”/home/mydir/memleak_

For tests that support the TOPOTESTS_CHECK_MEMLEAK environment variable, this will enable output to the information to files with the given prefix (followed by testname), e.g.,: file:/home/mydir/memcheck_test_bgp_multiview_topo1.txt in case of a memory leak.

Detecting Memleaks with Valgrind

Topotest can automatically launch all daemons with valgrind to check for memleaks. This is enabled by specifying 1 or 2 CLI arguments. --valgrind-memleaks will enable general memleak detection, and --valgrind-extra enables extra functionality including generating a suppression file. The suppression file tools/valgrind.supp is used when memleak detection is enabled.

sudo -E pytest --valgrind-memleaks all-protocol-startup

Collecting Performance Data using perf(1)

Topotest can automatically launch any daemon under perf(1) to collect performance data. The daemon is run in non-daemon mode with perf record -g. The file will be saved in the router specific directory under the tests run directoy.

Here’s an example of collecting performance data from mgmtd on router r1 during the config_timing test.

$ sudo -E pytest --perf=mgmtd,r1 config_timing
$ find /tmp/topotests/ -name '**'

To specify different arguments for perf record, one can use the --perf-options this will replace the -g used by default.

Running Tests with Docker

There is a Docker image which allows to run topotests.


If you have Docker installed, you can run the topotests in Docker. The easiest way to do this, is to use the make targets from this repository.

Your current user needs to have access to the Docker daemon. Alternatively you can run these commands as root.

make topotests

This command will pull the most recent topotests image from Dockerhub, compile FRR inside of it, and run the topotests.

Advanced Usage

Internally, the topotests make target uses a shell script to pull the image and spawn the Docker container.

There are several environment variables which can be used to modify the behavior of the script, these can be listed by calling it with -h:

./tests/topotests/docker/ -h

For example, a volume is used to cache build artifacts between multiple runs of the image. If you need to force a complete recompile, you can set TOPOTEST_CLEAN:

TOPOTEST_CLEAN=1 ./tests/topotests/docker/

By default, will build frr and run pytest. If you append arguments and the first one starts with / or ./, they will replace the call to pytest. If the appended arguments do not match this patttern, they will be provided to pytest as arguments. So, to run a specific test with more verbose logging:

./tests/topotests/docker/ -vv -s all-protocol-startup/

And to compile FRR but drop into a shell instead of running pytest:

./tests/topotests/docker/ /bin/bash


The Docker image just includes all the components to run the topotests, but not the topotests themselves. So if you just want to write tests and don’t want to make changes to the environment provided by the Docker image. You don’t need to build your own Docker image if you do not want to.

When developing new tests, there is one caveat though: The startup script of the container will run a git-clean on its copy of the FRR tree to avoid any pollution of the container with build artefacts from the host. This will also result in your newly written tests being unavailable in the container unless at least added to the index with git-add.

If you do want to test changes to the Docker image, you can locally build the image and run the tests without pulling from the registry using the following commands:

make topotests-build
TOPOTEST_PULL=0 make topotests


Executing Tests

To run the whole suite of tests the following commands must be executed at the top level directory of topotest:

$ # Change to the top level directory of topotests.
$ cd path/to/topotests
$ # Tests must be run as root, since micronet requires it.
$ sudo -E pytest

In order to run a specific test, you can use the following command:

$ # running a specific topology
$ sudo -E pytest ospf-topo1/
$ # or inside the test folder
$ cd ospf-topo1
$ sudo -E pytest # to run all tests inside the directory
$ sudo -E pytest # to run a specific test
$ # or outside the test folder
$ cd ..
$ sudo -E pytest ospf-topo1/ # to run a specific one

The output of the tested daemons will be available at the temporary folder of your machine:

$ ls /tmp/topotest/ospf-topo1.test_ospf-topo1/r1
zebra.err # zebra stderr output
zebra.log # zebra log file
zebra.out # zebra stdout output

You can also run memory leak tests to get reports:

$ # Set the environment variable to apply to a specific test...
$ sudo -E env TOPOTESTS_CHECK_MEMLEAK="/tmp/memleak_report_" pytest ospf-topo1/
$ # ...or apply to all tests adding this line to the configuration file
$ echo 'memleak_path = /tmp/memleak_report_' >> pytest.ini
$ # You can also use your editor
$ $EDITOR pytest.ini
$ # After running tests you should see your files:
$ ls /tmp/memleak_report_*

Writing a New Test

This section will guide you in all recommended steps to produce a standard topology test.

This is the recommended test writing routine:

  • Write a topology (Graphviz recommended)

  • Obtain configuration files

  • Write the test itself

  • Format the new code using black

  • Create a Pull Request

Some things to keep in mind:

  • BGP tests MUST use generous convergence timeouts - you must ensure that any test involving BGP uses a convergence timeout of at least 130 seconds.

  • Topotests are run on a range of Linux versions: if your test requires some OS-specific capability (like mpls support, or vrf support), there are test functions available in the libraries that will help you determine whether your test should run or be skipped.

  • Avoid including unstable data in your test: don’t rely on link-local addresses or ifindex values, for example, because these can change from run to run.

  • Using sleep is almost never appropriate. As an example: if the test resets the peers in BGP, the test should look for the peers re-converging instead of just sleeping an arbitrary amount of time and continuing on. See verify_bgp_convergence as a good example of this. In particular look at it’s use of the @retry decorator. If you are having troubles figuring out what to look for, please do not be afraid to ask.

  • Don’t duplicate effort. There exists many protocol utility functions that can be found in their eponymous module under tests/topotests/lib/ (e.g.,

Topotest File Hierarchy

Before starting to write any tests one must know the file hierarchy. The repository hierarchy looks like this:

$ cd path/to/topotest
$ find ./*
./ # repository read me
./ # this file
./ # test hooks - pytest related functions
./example-test # example test folder
./example-test/ # python package marker - must always exist.
./example-test/test_template.jpg # generated topology picture - see next section
./example-test/ # Graphviz dot file
./example-test/ # the topology plus the test
./ospf-topo1 # the ospf topology test
./ospf-topo1/r1 # router 1 configuration files
./ospf-topo1/r1/zebra.conf # zebra configuration file
./ospf-topo1/r1/ospfd.conf # ospf configuration file
./ospf-topo1/r1/ospfroute.txt # 'show ip ospf' output reference file
# removed other for shortness sake
./lib # shared test/topology functions
./lib/ # topogen implementation
./lib/ # topotest implementation

Guidelines for creating/editing topotest:

  • New topologies that don’t fit the existing directories should create its own

  • Always remember to add the to new folders, this makes auto complete engines and pylint happy

  • Router (Quagga/FRR) specific code should go on

  • Generic/repeated router actions should have an abstraction in topogen.TopoRouter.

  • Generic/repeated non-router code should go to

  • pytest related code should go to (e.g. specialized asserts)

Defining the Topology

The first step to write a new test is to define the topology. This step can be done in many ways, but the recommended is to use Graphviz to generate a drawing of the topology. It allows us to see the topology graphically and to see the names of equipment, links and addresses.

Here is an example of Graphviz dot file that generates the template topology tests/topotests/example-test/ (the inlined code might get outdated, please see the linked file):

graph template {

    # Routers
    r1 [
    r2 [

    # Switches
    s1 [
    s2 [

    # Connections
    r1 -- s1 [label="eth0\n.1"];

    r1 -- s2 [label="eth1\n.100"];
    r2 -- s2 [label="eth0\n.1"];

Here is the produced graph:

graph template {

    # Routers
    r1 [
    r2 [

    # Switches
    s1 [
    s2 [

    # Connections
    r1 -- s1 [label="eth0\n.1"];

    r1 -- s2 [label="eth1\n.100"];
    r2 -- s2 [label="eth0\n.1"];

Generating / Obtaining Configuration Files

In order to get the configuration files or command output for each router, we need to run the topology and execute commands in vtysh. The quickest way to achieve that is writing the topology building code and running the topology.

To bootstrap your test topology, do the following steps:

  • Copy the template test

$ mkdir new-topo/
$ touch new-topo/
$ cp example-test/ new-topo/
  • Modify the template according to your dot file

Here is the template topology described in the previous section in python code:

topodef = {
    "s1": "r1"
    "s2": ("r1", "r2")

If more specialized topology definitions, or router initialization arguments are required a build function can be used instead of a dictionary:

def build_topo(tgen):
    "Build function"

    # Create 2 routers
    for routern in range(1, 3):

    # Create a switch with just one router connected to it to simulate a
    # empty network.
    switch = tgen.add_switch("s1")

    # Create a connection between r1 and r2
    switch = tgen.add_switch("s2")
  • Run the topology

Topogen allows us to run the topology without running any tests, you can do that using the following example commands:

$ # Running your bootstraped topology
$ sudo -E pytest -s --topology-only new-topo/
$ # Running the topology
$ sudo -E pytest -s --topology-only example-test/
$ # Running the topology
$ sudo -E pytest -s --topology-only ospf-topo1/

Parameters explanation:


Actives input/output capture. If this is not specified a new window will be opened for the interactive CLI, otherwise it will be activated inline.


Don’t run any tests, just build the topology.

After executing the commands above, you should get the following terminal output:

frr/tests/topotests# sudo -E pytest -s --topology-only ospf_topo1/
============================= test session starts ==============================
platform linux -- Python 3.9.2, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /home/chopps/w/frr/tests/topotests, configfile: pytest.ini
plugins: forked-1.3.0, xdist-2.3.0
collected 11 items


The last line shows us that we are now using the CLI (Command Line Interface), from here you can call your router vtysh or even bash.

Here’s the help text:

unet> help

  help                       :: this help
  sh [hosts] <shell-command> :: execute <shell-command> on <host>
  term [hosts]               :: open shell terminals for hosts
  vtysh [hosts]              :: open vtysh terminals for hosts
  [hosts] <vtysh-command>    :: execute vtysh-command on hosts

Here are some commands example:

unet> sh r1 ping
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=0.576 ms
64 bytes from icmp_seq=2 ttl=64 time=0.083 ms
64 bytes from icmp_seq=3 ttl=64 time=0.088 ms
--- ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.083/0.249/0.576/0.231 ms

unet> r1 show run
Building configuration...

Current configuration:
frr version 8.1-dev-my-manual-build
frr defaults traditional
hostname r1
log file /tmp/topotests/ospf_topo1.test_ospf_topo1/r1/zebra.log

unet> show daemons
------ Host: r1 ------
 zebra ospfd ospf6d staticd
------- End: r1 ------
------ Host: r2 ------
 zebra ospfd ospf6d staticd
------- End: r2 ------
------ Host: r3 ------
 zebra ospfd ospf6d staticd
------- End: r3 ------
------ Host: r4 ------
 zebra ospfd ospf6d staticd
------- End: r4 ------

After you successfully configured your topology, you can obtain the configuration files (per-daemon) using the following commands:

unet> sh r3 vtysh -d ospfd

Hello, this is FRRouting (version 3.1-devrzalamena-build).
Copyright 1996-2005 Kunihiro Ishiguro, et al.

r1# show running-config
Building configuration...

Current configuration:
frr version 3.1-devrzalamena-build
frr defaults traditional
no service integrated-vtysh-config
log file ospfd.log
router ospf
 ospf router-id
 redistribute kernel
 redistribute connected
 redistribute static
 network area 0
 network area 0
 network area 1
line vty

You can also login to the node specified by nsenter using bash, etc. A pid file for each node will be created in the relevant test dir. You can run scripts inside the node, or use vtysh’s <tab> or <?> feature.

[unet shell]
# cd tests/topotests/srv6_locator
# ./ --topology-only
unet> r1 show segment-routing srv6 locator
Name                 ID      Prefix                   Status
-------------------- ------- ------------------------ -------
loc1                       1 2001:db8:1:1::/64        Up
loc2                       2 2001:db8:2:2::/64        Up

[Another shell]
# nsenter -a -t $(cat /tmp/topotests/srv6_locator.test_srv6_locator/ bash --norc
# vtysh
r1# r1 show segment-routing srv6 locator
Name                 ID      Prefix                   Status
-------------------- ------- ------------------------ -------
loc1                       1 2001:db8:1:1::/64        Up
loc2                       2 2001:db8:2:2::/64        Up

Writing Tests

Test topologies should always be bootstrapped from tests/topotests/example_test/ because it contains important boilerplate code that can’t be avoided, like:


# For all routers arrange for:
# - starting zebra using config file from <rtrname>/zebra.conf
# - starting ospfd using an empty config file.
for rname, router in router_list.items():
    router.load_config(TopoRouter.RD_ZEBRA, "zebra.conf")
  • The topology definition or build function

topodef = {
    "s1": ("r1", "r2"),
    "s2": ("r2", "r3")

def build_topo(tgen):
    # topology build code
  • pytest setup/teardown fixture to start the topology and supply tgen argument to tests.

def tgen(request):
    "Setup/Teardown the environment and provide tgen argument to tests"

    tgen = Topogen(topodef, module.__name__)
    # or
    tgen = Topogen(build_topo, module.__name__)


    # Start and configure the router daemons

    # Provide tgen as argument to each test function
    yield tgen

    # Teardown after last test runs


  • Directory name for a new topotest must not contain hyphen (-) characters. To separate words, use underscores (_). For example, tests/topotests/bgp_new_example.

  • Test code should always be declared inside functions that begin with the test_ prefix. Functions beginning with different prefixes will not be run by pytest.

  • Configuration files and long output commands should go into separated files inside folders named after the equipment.

  • Tests must be able to run without any interaction. To make sure your test conforms with this, run it without the -s parameter.

  • Use black code formatter before creating a pull request. This ensures we have a unified code style.

  • Mark test modules with pytest markers depending on the daemons used during the tests (see Markers)

  • Always use IPv4 RFC 5737 (,, and IPv6 RFC 3849 (2001:db8::/32) ranges reserved for documentation.


  • Keep results in stack variables, so people inspecting code with pdb can easily print their values.

Don’t do this:

assert foobar(router1, router2)

Do this instead:

result = foobar(router1, router2)
assert result
  • Use assert messages to indicate where the test failed.


for router in router_list:
   # ...
   assert condition, 'Router "{}" condition failed'.format(

Debugging Execution

The most effective ways to inspect topology tests are:

  • Run pytest with --pdb option. This option will cause a pdb shell to appear when an assertion fails

Example: pytest -s --pdb ospf-topo1/

  • Set a breakpoint in the test code with pdb


# Add the pdb import at the beginning of the file
import pdb
# ...

# Add a breakpoint where you think the problem is
def test_bla():
  # ...
  # ...

The Python Debugger (pdb) shell allows us to run many useful operations like:

  • Setting breaking point on file/function/conditions (e.g. break, condition)

  • Inspecting variables (e.g. p (print), pp (pretty print))

  • Running python code


The TopoGear (equipment abstraction class) implements the __str__ method that allows the user to inspect equipment information.

Example of pdb usage:

> /media/sf_src/topotests/ospf-topo1/
-> for rnum in range(1, 5):
(Pdb) help
Documented commands (type help <topic>):
EOF    bt         cont      enable  jump  pp       run      unt
a      c          continue  exit    l     q        s        until
alias  cl         d         h       list  quit     step     up
args   clear      debug     help    n     r        tbreak   w
b      commands   disable   ignore  next  restart  u        whatis
break  condition  down      j       p     return   unalias  where

Miscellaneous help topics:
exec  pdb

Undocumented commands:
retval  rv

(Pdb) list
116                                   title2="Expected output")
118     def test_ospf_convergence():
119         "Test OSPF daemon convergence"
120         pdb.set_trace()
121  ->     for rnum in range(1, 5):
122             router = 'r{}'.format(rnum)
124             # Load expected results from the command
125             reffile = os.path.join(CWD, '{}/ospfroute.txt'.format(router))
126             expected = open(reffile).read()
(Pdb) step
> /media/sf_src/topotests/ospf-topo1/
-> router = 'r{}'.format(rnum)
(Pdb) step
> /media/sf_src/topotests/ospf-topo1/
-> reffile = os.path.join(CWD, '{}/ospfroute.txt'.format(router))
(Pdb) print rnum
(Pdb) print router
(Pdb) tgen = get_topogen()
(Pdb) pp tgen.gears[router]
<lib.topogen.TopoRouter object at 0x7f74e06c9850>
(Pdb) pp str(tgen.gears[router])
'TopoGear<name="r1",links=["r1-eth0"<->"s1-eth0","r1-eth1"<->"s3-eth0"]> TopoRouter<>'
(Pdb) l 125
120         pdb.set_trace()
121         for rnum in range(1, 5):
122             router = 'r{}'.format(rnum)
124             # Load expected results from the command
125  ->         reffile = os.path.join(CWD, '{}/ospfroute.txt'.format(router))
126             expected = open(reffile).read()
128             # Run test function until we get an result. Wait at most 60 seconds.
129             test_func = partial(compare_show_ip_ospf, router, expected)
130             result, diff = topotest.run_and_expect(test_func, '',
(Pdb) router1 = tgen.gears[router]
(Pdb) router1.vtysh_cmd('show ip ospf route')
'============ OSPF network routing table ============\r\nN           [10] area:\r\n                           directly attached to r1-eth0\r\nN           [20] area:\r\n                           via, r1-eth1\r\nN           [10] area:\r\n                           directly attached to r1-eth1\r\nN          [20] area:\r\n                           via, r1-eth1\r\nN IA         [20] area:\r\n                           via, r1-eth1\r\nN IA         [30] area:\r\n                           via, r1-eth1\r\n\r\n============ OSPF router routing table =============\r\nR            [10] area:, ASBR\r\n                           via, r1-eth1\r\nR            [10] area:, ABR, ASBR\r\n                           via, r1-eth1\r\nR         IA [20] area:, ASBR\r\n                           via, r1-eth1\r\n\r\n============ OSPF external routing table ===========\r\n\r\n\r\n'
 (Pdb) tgen.cli()

To enable more debug messages in other Topogen subsystems, more logging messages can be displayed by modifying the test configuration file pytest.ini:

# Change the default verbosity line from 'info'...
#verbosity = info
# 'debug'
verbosity = debug

Instructions for use, write or debug topologies can be found in Guidelines. To learn/remember common code snippets see Snippets.

Before creating a new topology, make sure that there isn’t one already that does what you need. If nothing is similar, then you may create a new topology, preferably, using the newest template (tests/topotests/example-test/


To allow for automated selective testing on large scale continuous integration systems, all tests must be marked with at least one of the following markers:

  • babeld

  • bfdd

  • bgpd

  • eigrpd

  • isisd

  • ldpd

  • nhrpd

  • ospf6d

  • ospfd

  • pathd

  • pbrd

  • pimd

  • ripd

  • ripngd

  • sharpd

  • staticd

  • vrrpd

The markers corespond to the daemon subdirectories in FRR’s source code and have to be added to tests on a module level depending on which daemons are used during the test.

The goal is to have continuous integration systems scan code submissions, detect changes to files in a daemons subdirectory and select only tests using that daemon to run to shorten developers waiting times for test results and save test infrastructure resources.

Newly written modules and code changes on tests, which do not contain any or incorrect markers will be rejected by reviewers.

Registering markers

The Registration of new markers takes place in the file tests/topotests/pytest.ini:

# tests/topotests/pytest.ini
markers =
    babeld: Tests that run against BABELD
    bfdd: Tests that run against BFDD
    vrrpd: Tests that run against VRRPD

Adding markers to tests

Markers are added to a test by placing a global variable in the test module.

Adding a single marker:

import pytest

# add after imports, before defining classes or functions:
pytestmark = pytest.mark.bfdd


def test_using_bfdd():

Adding multiple markers:

import pytest

# add after imports, before defining classes or functions:
pytestmark = [


def test_using_bgpd_ospfd_ospf6d():

Selecting marked modules for testing

Selecting by a single marker:

pytest -v -m isisd

Selecting by multiple markers:

pytest -v -m "isisd or ldpd or nhrpd"

Further Information

The online pytest documentation provides further information and usage examples for pytest markers.


This document will describe common snippets of code that are frequently needed to perform some test checks.

Checking for router / test failures

The following check uses the topogen API to check for software failure (e.g. zebra died) and/or for errors manually set by Topogen.set_error().

# Get the topology reference
tgen = get_topogen()

# Check for errors in the topology
if tgen.routers_have_failure():
    # Skip the test with the topology errors as reason

Checking FRR routers version

This code snippet is usually run after the topology setup to make sure all routers instantiated in the topology have the correct software version.

# Get the topology reference
tgen = get_topogen()

# Get the router list
router_list = tgen.routers()

# Run the check for all routers
for router in router_list.values():
    if router.has_version('<', '3'):
        # Set topology error, so the next tests are skipped
        tgen.set_error('unsupported version')

A sample of this snippet in a test can be found here.

Interacting with equipment

You might want to interact with the topology equipment during the tests and there are different ways to do so.


  1. When using the Topogen API, all the equipment code derives from Topogear (lib/ If you feel brave you can look by yourself how the abstractions that will be mentioned here work.

  2. When not using the Topogen API there is only one way to interact with the equipment, which is by calling the mininet API functions directly to spawn commands.

Interacting with the Linux sandbox

Without Topogen:

global net
output = net['r1'].cmd('echo "foobar"')
print 'output is: {}'.format(output)

With Topogen:

tgen = get_topogen()
output = tgen.gears['r1'].run('echo "foobar"')
print 'output is: {}'.format(output)

Interacting with VTYSH

Without Topogen:

global net
output = net['r1'].cmd('vtysh "show ip route" 2>/dev/null')
print 'output is: {}'.format(output)

With Topogen:

tgen = get_topogen()
output = tgen.gears['r1'].vtysh_cmd("show ip route")
print 'output is: {}'.format(output)

Topogen also supports sending multiple lines of command:

tgen = get_topogen()
output = tgen.gears['r1'].vtysh_cmd("""
configure terminal
router bgp 10
  bgp router-id
  neighbor remote-as 10
router bgp 11
  bgp router-id
print 'output is: {}'.format(output)

You might also want to run multiple commands and get only the commands that failed:

tgen = get_topogen()
output = tgen.gears['r1'].vtysh_multicmd("""
configure terminal
router bgp 10
  bgp router-id
  neighbor remote-as 10
router bgp 11
  bgp router-id
""", pretty_output=false)
print 'output is: {}'.format(output)

Translating vtysh JSON output into Python structures:

tgen = get_topogen()
json_output = tgen.gears['r1'].vtysh_cmd("show ip route json", isjson=True)
output = json.dumps(json_output, indent=4)
print 'output is: {}'.format(output)

# You can also access the data structure as normal. For example:
# protocol = json_output['']['protocol']
# assert protocol == "ospf", "wrong protocol"


vtysh_(multi)cmd is only available for router types of equipment.

Invoking mininet CLI

Without Topogen:


With Topogen:

tgen = get_topogen()

Reading files

Loading a normal text file content in the current directory:

# If you are using Topogen
# Otherwise find the directory manually:
CURDIR = os.path.dirname(os.path.realpath(__file__))

file_name = '{}/r1/show_ip_route.txt'.format(CURDIR)
file_content = open(file_name).read()

Loading JSON from a file:

import json

file_name = '{}/r1/show_ip_route.json'.format(CURDIR)
file_content = json.loads(open(file_name).read())

Comparing JSON output

After obtaining JSON output formatted with Python data structures, you may use it to assert a minimalist schema:

tgen = get_topogen()
json_output = tgen.gears['r1'].vtysh_cmd("show ip route json", isjson=True)

expect = {
  '': {
    'protocol': 'ospf'

assertmsg = "route was not learned through OSPF"
assert json_cmp(json_output, expect) is None, assertmsg

json_cmp function description (it might be outdated, you can find the latest description in the source code at tests/topotests/lib/

JSON compare function. Receives two parameters:
* `d1`: json value
* `d2`: json subset which we expect

Returns `None` when all keys that `d1` has matches `d2`,
otherwise a string containing what failed.

Note: key absence can be tested by adding a key with value `None`.

Pausing execution

Preferably, choose the sleep function that topotest provides, as it prints a notice during the test execution to help debug topology test execution time.

# Using the topotest sleep
from lib import topotest

topotest.sleep(10, 'waiting 10 seconds for bla')
# or just tell it the time:
# topotest.sleep(10)
# It will print 'Sleeping for 10 seconds'.

# Or you can also use the Python sleep, but it won't show anything
from time import sleep

iproute2 Linux commands as JSON

topotest has two helpers implemented that parses the output of ip route commands to JSON. It might simplify your comparison needs by only needing to provide a Python dictionary.

from lib import topotest

tgen = get_topogen()
routes = topotest.ip4_route(tgen.gears['r1'])
expected = {
  '': {},
  '': {
    'dev': 'r1-eth0'

assertmsg = "failed to find and/or"
assert json_cmp(routes, expected) is None, assertmsg


All the configs and scripts are licensed under a ISC-style license. See Python scripts for details.