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<h1>Troubleshooting common problems</h1>
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<h5>Table of Contents</h5>
<ul id="markdown-toc">
<li><a href="#multibodyplant" id="markdown-toc-multibodyplant">MultibodyPlant</a> <ul>
<li><a href="#mbp-parsing" id="markdown-toc-mbp-parsing">Parsing</a></li>
<li><a href="#mbp-unconnected-query-object-port" id="markdown-toc-mbp-unconnected-query-object-port">Unconnected QueryObject port</a></li>
</ul>
</li>
<li><a href="#system-framework" id="markdown-toc-system-framework">System Framework</a> <ul>
<li><a href="#framework-context-system-mismatch" id="markdown-toc-framework-context-system-mismatch">Context-System mismatch</a></li>
</ul>
</li>
<li><a href="#pypi-pip" id="markdown-toc-pypi-pip">PyPI (pip)</a> <ul>
<li><a href="#pip-no-candidate" id="markdown-toc-pip-no-candidate">No candidate version for this platform</a></li>
</ul>
</li>
<li><a href="#image-rendering" id="markdown-toc-image-rendering">Image rendering</a> <ul>
<li><a href="#gl-init" id="markdown-toc-gl-init">GL and/or DISPLAY</a></li>
</ul>
</li>
<li><a href="#build-problems" id="markdown-toc-build-problems">Build problems</a> <ul>
<li><a href="#build-oom" id="markdown-toc-build-oom">Out of memory</a></li>
</ul>
</li>
<li><a href="#network-configuration" id="markdown-toc-network-configuration">Network Configuration</a> <ul>
<li><a href="#lcm-macos" id="markdown-toc-lcm-macos">LCM on macOS</a></li>
</ul>
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<article class="markdown-body">
<p>This page contains a collection of tips and tricks for resolving common
problems.</p>
<h1 id="multibodyplant">MultibodyPlant</h1>
<h2 id="mbp-parsing">Parsing</h2>
<p>If you have a model file (e.g., .urdf, .sdf, .xml, .usd, etc.) that you are loading into a <code class="language-plaintext highlighter-rouge">MultibodyPlant</code> using the <code class="language-plaintext highlighter-rouge">Parser</code> class, and the model is not loading properly, then there are a few useful resources you might consider.</p>
<p>Documentation for the specific XML elements and attributes supported by the parser can be found <a href="https://drake.mit.edu/doxygen_cxx/group__multibody__parsing.html">here</a>.</p>
<p>If you do run into some of the known limitations in Drake’s parsing support, you may consider using the <a href="https://manipulation.mit.edu/python/make_drake_compatible_model.html"><code class="language-plaintext highlighter-rouge">make_drake_compatible_model</code></a> tool to convert your model file and assets into a format that Drake can parse. It is available in the <a href="https://manipulation.mit.edu/">manipulation</a> Python package, and be used via e.g.:</p>
<div class="language-bash highlighter-rouge"><div class="highlight"><pre class="highlight"><code>python3 <span class="nt">-m</span> venv venv
venv/bin/pip <span class="nb">install </span>manipulation[mesh] <span class="nt">--extra-index-url</span> https://drake-packages.csail.mit.edu/whl/nightly/
venv/bin/python <span class="nt">-m</span> manipulation.make_drake_compatible_model <span class="o">{</span>input_file<span class="o">}</span> <span class="o">{</span>output_file<span class="o">}</span>
</code></pre></div> </div>
<h2 id="mbp-unconnected-query-object-port">Unconnected QueryObject port</h2>
<p>The error message will include the message, “The provided context doesn’t show a
connection for the plant’s query input port.”</p>
<p><code class="language-plaintext highlighter-rouge">MultibodyPlant</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1multibody_1_1_multibody_plant.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.multibody.plant.html#pydrake.multibody.plant.MultibodyPlant">Python</a>)
requires a connection to <code class="language-plaintext highlighter-rouge">SceneGraph</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1geometry_1_1_scene_graph.html">C++</a>,
<a href="https://drake.mit.edu/pydrake/pydrake.geometry.html#pydrake.geometry.SceneGraph_">Python</a>) in order to evaluate contact via its <code class="language-plaintext highlighter-rouge">QueryObject</code>
(<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1geometry_1_1_query_object.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.geometry.html#pydrake.geometry.QueryObject_">Python</a>). Attempts to evaluate output
ports that expose or depend on contact results (the geometric data and/or forces
that arise from the contact between bodies’ collision geometries) will fail.
Evaluating the time derivatives (e.g., when running a continuous simulation)
will likewise fail.</p>
<p>The connection can be reported as missing for several reasons:</p>
<ol>
<li>Was a <code class="language-plaintext highlighter-rouge">SceneGraph</code> instance created and connected?
<ul>
<li>The simplest solution is to use <code class="language-plaintext highlighter-rouge">AddMultibodyPlantSceneGraph()</code>
(<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1multibody_1_1_multibody_plant.html#aac66563a5f3eb9e2041bd4fa8d438827">C++</a>,
<a href="https://drake.mit.edu/pydrake/pydrake.multibody.plant.html#pydrake.multibody.plant.AddMultibodyPlantSceneGraph">Python</a>). It will construct and connect
the plant and scene graph together for you.</li>
</ul>
</li>
<li>Did you provide the right context?
<ul>
<li>You’ve created and connected the systems in a <code class="language-plaintext highlighter-rouge">Diagram</code>
(<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_diagram.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.Diagram">Python</a>) and allocated a <code class="language-plaintext highlighter-rouge">Context</code>
(<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_context.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.Context">Python</a>) for the <code class="language-plaintext highlighter-rouge">Diagram</code>.</li>
<li>Make sure you extract the <code class="language-plaintext highlighter-rouge">MultibodyPlant</code>’s context from the <code class="language-plaintext highlighter-rouge">Diagram</code>’s
<code class="language-plaintext highlighter-rouge">Context</code>. Do not allocate a <code class="language-plaintext highlighter-rouge">Context</code> directly from the plant. Use
<code class="language-plaintext highlighter-rouge">System::GetMyContextFromRoot()</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_system.html#ae7fa91d2b2102457ced3361207724e52">C++</a>,
<a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.System_.System_[float].GetMyMutableContextFromRoot">Python</a>) to acquire the plant’s <code class="language-plaintext highlighter-rouge">Context</code> from the
<code class="language-plaintext highlighter-rouge">Diagram</code>’s context; this will preserve all of the necessary connections.
E.g.,</li>
</ul>
<div class="language-py highlighter-rouge"><div class="highlight"><pre class="highlight"><code> <span class="n">builder</span> <span class="o">=</span> <span class="n">DiagramBuilder</span><span class="p">()</span>
<span class="c1"># Build plant and scene graph and automatically connect them.
</span> <span class="n">plant</span><span class="p">,</span> <span class="n">scene_graph</span> <span class="o">=</span> <span class="n">AddMultibodyPlantSceneGraph</span><span class="p">(</span>
<span class="n">builder</span><span class="o">=</span><span class="n">builder</span><span class="p">,</span> <span class="n">time_step</span><span class="o">=</span><span class="mf">1e-3</span><span class="p">)</span>
<span class="p">...</span>
<span class="n">diagram</span> <span class="o">=</span> <span class="n">builder</span><span class="p">.</span><span class="n">Build</span><span class="p">()</span>
<span class="c1"># WRONG. This will create a Context for the plant only (no connected
</span> <span class="c1"># SceneGraph).
</span> <span class="n">xdot</span> <span class="o">=</span> <span class="n">plant</span><span class="p">.</span><span class="n">EvalTimeDerivatives</span><span class="p">(</span><span class="n">context</span><span class="o">=</span><span class="n">plant</span><span class="p">.</span><span class="n">CreateDefaultContext</span><span class="p">())</span>
<span class="n">context</span> <span class="o">=</span> <span class="n">diagram</span><span class="p">.</span><span class="n">CreateDefaultContext</span><span class="p">()</span>
<span class="c1"># Extract the plant's context from the diagram's to invoke plant methods.
</span> <span class="n">plant_context</span> <span class="o">=</span> <span class="n">plant</span><span class="p">.</span><span class="n">GetMyContextFromRoot</span><span class="p">(</span><span class="n">root_context</span><span class="o">=</span><span class="n">context</span><span class="p">)</span>
<span class="n">xdot</span> <span class="o">=</span> <span class="n">plant</span><span class="p">.</span><span class="n">EvalTimeDerivatives</span><span class="p">(</span><span class="n">context</span><span class="o">=</span><span class="n">plant_context</span><span class="p">)</span>
</code></pre></div> </div>
</li>
</ol>
<h1 id="system-framework">System Framework</h1>
<h2 id="framework-context-system-mismatch">Context-System mismatch</h2>
<p>The error message will include one of the following:</p>
<ul>
<li><code class="language-plaintext highlighter-rouge">A function call on a FooSystem system named '::_::foo' was passed the root
Diagram's Context instead of the appropriate subsystem context.</code></li>
<li><code class="language-plaintext highlighter-rouge">A function call on the root Diagram was passed a subcontext associated with
its subsystem named '::_::foo' instead of the root context.</code></li>
<li><code class="language-plaintext highlighter-rouge">A function call on a BarSystem named '::_::bar' was passed the Context of
a system named '::_::foo' instead of the appropriate subsystem Context.</code></li>
</ul>
<!-- TODO(SeanCurtis-TRI): This overview of Systems and Contexts would be
better in a doxygen module and just referenced here. Ping Russ to see if his
textbook covers this material and if we can/should steal it. -->
<h4>Contexts and Systems: An Overview</h4>
<p>For every <code class="language-plaintext highlighter-rouge">System</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_system.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.System">Python</a>) there is a
corresponding <code class="language-plaintext highlighter-rouge">Context</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_context.html">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.Context">Python</a>). The <code class="language-plaintext highlighter-rouge">System</code>
and <code class="language-plaintext highlighter-rouge">Context</code> work together. The <code class="language-plaintext highlighter-rouge">Context</code> holds the data values and the
<code class="language-plaintext highlighter-rouge">System</code> defines the operations on that data.</p>
<p>For example, a <code class="language-plaintext highlighter-rouge">MultibodyPlant</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1multibody_1_1_multibody_plant.html">C++</a>,
<a href="https://drake.mit.edu/pydrake/pydrake.multibody.plant.html#pydrake.multibody.plant.MultibodyPlant">Python</a>) is such a system. We can use an instance of a
<code class="language-plaintext highlighter-rouge">MultibodyPlant</code> to create one or more <code class="language-plaintext highlighter-rouge">Context</code>s. Each <code class="language-plaintext highlighter-rouge">Context</code> contains the
continuous and discrete state values for the plant’s model. These <code class="language-plaintext highlighter-rouge">Context</code>s
can be configured to represent the model in different configurations. However,
if we want to evaluate some mechanical property (e.g., composite inertia of a
robotic arm), we invoke a method on the plant, passing one of the contexts.</p>
<p>We can combine multiple <code class="language-plaintext highlighter-rouge">System</code>s into a <code class="language-plaintext highlighter-rouge">Diagram</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_diagram.html">C++</a>,
<a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.Diagram">Python</a>). The <code class="language-plaintext highlighter-rouge">System</code>s within a <code class="language-plaintext highlighter-rouge">Diagram</code> will typically have their
ports connected – this is how the <code class="language-plaintext highlighter-rouge">System</code>s work together.</p>
<p><code class="language-plaintext highlighter-rouge">Context</code>s similarly form a parallel hierarchical structure. The <code class="language-plaintext highlighter-rouge">Context</code>
associated with a <code class="language-plaintext highlighter-rouge">Diagram</code> is the combination of all of the <code class="language-plaintext highlighter-rouge">Context</code>s
associated with the <code class="language-plaintext highlighter-rouge">System</code>s inside that <code class="language-plaintext highlighter-rouge">Diagram</code>. The port connections
between <code class="language-plaintext highlighter-rouge">System</code>s in the <code class="language-plaintext highlighter-rouge">Diagram</code> are mirrored in the <code class="language-plaintext highlighter-rouge">Diagram</code>’s <code class="language-plaintext highlighter-rouge">Context</code>.</p>
<h4>Why did I get this error and how do I get rid of it?</h4>
<p>Many <code class="language-plaintext highlighter-rouge">System</code> APIs require a <code class="language-plaintext highlighter-rouge">Context</code>. It is important to pass the <em>right</em>
<code class="language-plaintext highlighter-rouge">Context</code> into the API. What’s the difference between a “right” and “wrong”
<code class="language-plaintext highlighter-rouge">Context</code>?</p>
<ul>
<li>The right <code class="language-plaintext highlighter-rouge">Context</code> was allocated by the <code class="language-plaintext highlighter-rouge">System</code> being evaluated.</li>
<li>If the <code class="language-plaintext highlighter-rouge">System</code> is part of a <code class="language-plaintext highlighter-rouge">Diagram</code>, then the <code class="language-plaintext highlighter-rouge">Context</code> provided should
be a reference pointing inside the <code class="language-plaintext highlighter-rouge">Diagram</code>s <code class="language-plaintext highlighter-rouge">Context</code> (see below for how
to do this).</li>
</ul>
<p>The most common error is to pass the <code class="language-plaintext highlighter-rouge">Diagram</code>’s <code class="language-plaintext highlighter-rouge">Context</code> into a constituent
<code class="language-plaintext highlighter-rouge">System</code>’s API. We’ll illustrate this using a <code class="language-plaintext highlighter-rouge">Diagram</code> with a <code class="language-plaintext highlighter-rouge">MultibodyPlant</code>.
The solution is to use either <code class="language-plaintext highlighter-rouge">GetMyContextFromRoot()</code>
(<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_system.html#ae7fa91d2b2102457ced3361207724e52">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.System_.System_[float].GetMyMutableContextFromRoot">Python</a>) or
<code class="language-plaintext highlighter-rouge">GetMyMutableContextFromRoot()</code> (<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1systems_1_1_system.html#ae7fa91d2b2102457ced3361207724e52">C++</a>, <a href="https://drake.mit.edu/pydrake/pydrake.systems.framework.html#pydrake.systems.framework.System_.System_[float].GetMyMutableContextFromRoot">Python</a>) as appropriate to extract a particular
<code class="language-plaintext highlighter-rouge">System</code>’s <code class="language-plaintext highlighter-rouge">Context</code> from its <code class="language-plaintext highlighter-rouge">Diagram</code>’s <code class="language-plaintext highlighter-rouge">Context</code>.</p>
<div class="language-py highlighter-rouge"><div class="highlight"><pre class="highlight"><code> <span class="n">builder</span> <span class="o">=</span> <span class="n">DiagramBuilder</span><span class="p">()</span>
<span class="n">plant</span><span class="p">,</span> <span class="n">_</span> <span class="o">=</span> <span class="n">AddMultibodyPlantSceneGraph</span><span class="p">(</span><span class="n">builder</span><span class="o">=</span><span class="n">builder</span><span class="p">,</span> <span class="n">time_step</span><span class="o">=</span><span class="mf">1e-3</span><span class="p">)</span>
<span class="p">...</span> <span class="c1"># Populate the plant with interesting stuff.
</span> <span class="n">diagram</span> <span class="o">=</span> <span class="n">builder</span><span class="p">.</span><span class="n">Build</span><span class="p">()</span>
<span class="c1"># Create a Context for diagram.
</span> <span class="n">root_context</span> <span class="o">=</span> <span class="n">diagram</span><span class="p">.</span><span class="n">CreateDefaultContext</span><span class="p">()</span>
<span class="n">my_body</span> <span class="o">=</span> <span class="n">plant</span><span class="p">.</span><span class="n">GetBodyByName</span><span class="p">(</span><span class="s">"my_body"</span><span class="p">)</span>
<span class="n">X_WB</span> <span class="o">=</span> <span class="n">RigidTransform</span><span class="p">(...)</span> <span class="c1"># Define a pose for the body.
</span> <span class="c1"># Error! plant has been given diagram's context.
</span> <span class="n">plant</span><span class="p">.</span><span class="n">SetFreeBodyPose</span><span class="p">(</span><span class="n">context</span><span class="o">=</span><span class="n">root_context</span><span class="p">,</span> <span class="n">body</span><span class="o">=</span><span class="n">base</span><span class="p">,</span> <span class="n">X_WB</span><span class="o">=</span><span class="n">X_WB_desired</span><span class="p">)</span>
<span class="c1"># Get the Context for plant from diagram's context.
</span> <span class="n">plant_context</span> <span class="o">=</span> <span class="n">plant</span><span class="p">.</span><span class="n">GetMyContextFromRoot</span><span class="p">(</span><span class="n">root_context</span><span class="o">=</span><span class="n">root_context</span><span class="p">)</span>
<span class="c1"># Successful operation; the provided context belongs to plant.
</span> <span class="n">plant</span><span class="p">.</span><span class="n">SetFreeBodyPose</span><span class="p">(</span><span class="n">context</span><span class="o">=</span><span class="n">plant_context</span><span class="p">,</span> <span class="n">body</span><span class="o">=</span><span class="n">base</span><span class="p">,</span> <span class="n">X_WB</span><span class="o">=</span><span class="n">X_WB_desired</span><span class="p">)</span>
</code></pre></div> </div>
<p>See the notes on <a href="https://drake.mit.edu/doxygen_cxx/group__system__compatibility.html">System Compatibility</a> for further discussion.</p>
<h1 id="pypi-pip">PyPI (pip)</h1>
<h2 id="pip-no-candidate">No candidate version for this platform</h2>
<!-- Even though this is only relevant to past versions of Drake that are no
longer supported, we'll keep this text around to help users of those older
versions. -->
<p>When installing Drake from PyPI on older platforms such as Ubuntu Focal, you may
receive the error “no candidate version for this platform”. This is caused by
older versions of <code class="language-plaintext highlighter-rouge">pip</code> which do not recognize the <code class="language-plaintext highlighter-rouge">manylinux</code> platform used by
Drake. This is remedied by installing a newer version of <code class="language-plaintext highlighter-rouge">pip</code>.</p>
<p>Use of a Python virtual environment may be required in order to get a newer
version of <code class="language-plaintext highlighter-rouge">pip</code>, e.g.:</p>
<div class="language-bash highlighter-rouge"><div class="highlight"><pre class="highlight"><code>python3 <span class="nt">-m</span> venv <span class="nb">env
env</span>/bin/pip <span class="nb">install</span> <span class="nt">--upgrade</span> pip
<span class="nb">env</span>/bin/pip <span class="nb">install </span>drake
<span class="nb">source env</span>/bin/activate
</code></pre></div> </div>
<h1 id="image-rendering">Image rendering</h1>
<h2 id="gl-init">GL and/or DISPLAY</h2>
<p>When performing image rendering (i.e., camera simulation), sometimes you may
need to configure your computer to provide Drake sufficient access to core
graphics libraries.</p>
<p>Drake renders images using the
<a href="https://drake.mit.edu/doxygen_cxx/classdrake_1_1geometry_1_1render_1_1_render_engine.html">RenderEngine</a>
abstract base class, which is typically configured using the
<a href="https://drake.mit.edu/doxygen_cxx/structdrake_1_1systems_1_1sensors_1_1_camera_config.html">CameraConfig</a>
data structure via YAML, which can specify a concrete <code class="language-plaintext highlighter-rouge">RenderEngine</code> subclass to
be used. Refer to the
<a href="https://github.com/RobotLocomotion/drake/tree/master/examples/hardware_sim">hardware_sim</a>
example for details.</p>
<p>If you are using either <code class="language-plaintext highlighter-rouge">RenderEngineGl</code>, or <code class="language-plaintext highlighter-rouge">RenderEngineVtk</code> under the
(non-default) setting <code class="language-plaintext highlighter-rouge">backend = "GLX"</code>, then you must ensure that prior to
using Drake the <code class="language-plaintext highlighter-rouge">$DISPLAY</code> environment variable is set to an available X11
display server (e.g., <code class="language-plaintext highlighter-rouge">":1"</code>). If you are running as desktop user (not over
ssh), then <code class="language-plaintext highlighter-rouge">$DISPLAY</code> will probably already be set correctly.</p>
<p>For remote rendering (e.g., in the cloud) we recommend avoiding needing any
<code class="language-plaintext highlighter-rouge">$DISPLAY</code> by using only <code class="language-plaintext highlighter-rouge">RenderEngineVtk</code> and only with its default <code class="language-plaintext highlighter-rouge">backend</code>.
If you do need a display in the cloud, you’ll need to run a program such as
<code class="language-plaintext highlighter-rouge">PyVirtualDisplay</code>, <code class="language-plaintext highlighter-rouge">Xvfb</code>, or a full <code class="language-plaintext highlighter-rouge">Xorg</code> server to provide it.</p>
<h1 id="build-problems">Build problems</h1>
<h2 id="build-oom">Out of memory</h2>
<p>When compiling Drake from source, the build might run out of memory. The error
message will include the message, “cc: fatal error: Killed signal terminated
program cc1plus”.</p>
<p>By default, the Drake build will try use all available CPU and RAM resources on
the machine. Sometimes, when there is not enough RAM per CPU, the build might
crash because it tried to run a compiler process on every vCPU and together
those compilation jobs consumed more RAM than was available.</p>
<p>In this case, you’ll need to add a bazel configuration dotfile to your home
directory. Create a text file at <code class="language-plaintext highlighter-rouge">$HOME/.bazelrc</code> with this content:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>build --jobs=HOST_CPUS*0.4
</code></pre></div> </div>
<p>This instructs the build system to use only 40% of the available vCPUs. You may
tune the fraction up or down to balance build speed vs resource crashes. You may
also specify an exact number like <code class="language-plaintext highlighter-rouge">build --jobs=2</code> instead of a fraction.</p>
<p>The dotfile will affect any Bazel builds that you run. If you prefer to change
only the Drake build instead of all Bazel builds, you may place the dotfile in
the Drake source tree at <code class="language-plaintext highlighter-rouge">drake/user.bazelrc</code> instead of your home directory.</p>
<p>Note that the concurrency level passed to <code class="language-plaintext highlighter-rouge">make</code> (e.g., <code class="language-plaintext highlighter-rouge">make -j 2</code>) does not
propagate through to affect the concurrency of most of Drake’s build steps; you
need to configure the dotfile in order to control the build concurrency.</p>
<h1 id="network-configuration">Network Configuration</h1>
<h2 id="lcm-macos">LCM on macOS</h2>
<p>When building and testing Drake from source on macOS 15 (Sequoia), you may
encounter issues with <a href="https://lcm-proj.github.io/lcm/index.html">LCM</a>.
In particular, an error message that can arise is: “LCM self test failed!!
Check your routing tables and firewall settings.” LCM relies on
<a href="https://lcm-proj.github.io/lcm/content/multicast-setup.html">UDP Multicast</a>
over loopback, so multicast traffic must be enabled over the loopback
interface on your computer in order for it to work.</p>
<p>Sometimes this is not explicitly enabled on macOS. If you see this error,
check the routing table by running <code class="language-plaintext highlighter-rouge">netstat -nr</code>. The following entry in the
IPv4 table is correct:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>Internet:
Destination Gateway Flags Netif Expire
...
224.0.0/4 lo0 UmS lo0
</code></pre></div> </div>
<p>If you see a different interface for this address, such as <code class="language-plaintext highlighter-rouge">en0</code>, then
run the following to change it to loopback (<code class="language-plaintext highlighter-rouge">lo0</code>):</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>sudo route -nv delete 224.0.0.0/4
sudo route -nv add -net 224.0.0.0/4 -interface lo0
</code></pre></div> </div>
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