face: allow GenericLinkService to override MTU

refs #5056

Change-Id: I8eb2dd732b1431e0e809deb53792a14be1698ff1
diff --git a/daemon/face/ethernet-channel.cpp b/daemon/face/ethernet-channel.cpp
index 0104b19..725bbfd 100644
--- a/daemon/face/ethernet-channel.cpp
+++ b/daemon/face/ethernet-channel.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -201,11 +201,13 @@
   options.allowFragmentation = true;
   options.allowReassembly = true;
   options.reliabilityOptions.isEnabled = params.wantLpReliability;
+  if (params.mtu) {
+    options.overrideMtu = *params.mtu;
+  }
 
   auto linkService = make_unique<GenericLinkService>(options);
   auto transport = make_unique<UnicastEthernetTransport>(*m_localEndpoint, remoteEndpoint,
-                                                         params.persistency, m_idleFaceTimeout,
-                                                         params.mtu);
+                                                         params.persistency, m_idleFaceTimeout);
   auto face = make_shared<Face>(std::move(linkService), std::move(transport));
 
   m_channelFaces[remoteEndpoint] = face;
diff --git a/daemon/face/ethernet-factory.cpp b/daemon/face/ethernet-factory.cpp
index 4d4d295..9659985 100644
--- a/daemon/face/ethernet-factory.cpp
+++ b/daemon/face/ethernet-factory.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -197,10 +197,10 @@
     return;
   }
 
-  if (req.params.mtu && *req.params.mtu < Transport::MIN_MTU) {
+  if (req.params.mtu && *req.params.mtu < MIN_MTU) {
     // The specified MTU must be greater than the minimum possible
-    NFD_LOG_TRACE("createFace cannot create a face with an MTU less than " << Transport::MIN_MTU);
-    onFailure(406, "MTU cannot be less than " + to_string(Transport::MIN_MTU));
+    NFD_LOG_TRACE("createFace: override MTU cannot be less than " << MIN_MTU);
+    onFailure(406, "Override MTU cannot be less than " + to_string(MIN_MTU));
     return;
   }
 
diff --git a/daemon/face/face-common.hpp b/daemon/face/face-common.hpp
index f233309..e2a0572 100644
--- a/daemon/face/face-common.hpp
+++ b/daemon/face/face-common.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -54,6 +54,12 @@
 /// upper bound of reserved FaceIds
 const FaceId FACEID_RESERVED_MAX = 255;
 
+/** \brief Minimum MTU that may be set
+ *
+ *  This is done to ensure the NDNLPv2 fragmentation feature functions properly.
+ */
+const ssize_t MIN_MTU = 64;
+
 /** \brief Identifies a remote endpoint on the link.
  *
  *  This ID is only meaningful in the context of the same Transport.
diff --git a/daemon/face/face.hpp b/daemon/face/face.hpp
index dc8c20d..4a5948b 100644
--- a/daemon/face/face.hpp
+++ b/daemon/face/face.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -60,6 +60,18 @@
   Transport*
   getTransport() const;
 
+  /** \brief Request that the face be closed
+   *
+   *  This operation is effective only if face is in the UP or DOWN state; otherwise, it has no effect.
+   *  The face will change state to CLOSING, and then perform a cleanup procedure.
+   *  When the cleanup is complete, the state will be changed to CLOSED, which may happen
+   *  synchronously or asynchronously.
+   *
+   *  \warning The face must not be deallocated until its state changes to CLOSED.
+   */
+  void
+  close();
+
 public: // upper interface connected to forwarding
   /** \brief send Interest to \p endpointId
    */
@@ -92,7 +104,7 @@
    */
   signal::Signal<LinkService, Interest>& onDroppedInterest;
 
-public: // static properties
+public: // properties
   /** \return face ID
    */
   FaceId
@@ -134,7 +146,13 @@
   ndn::nfd::LinkType
   getLinkType() const;
 
-public: // dynamic properties
+  /** \brief Returns face effective MTU
+   *
+   *  This function is a wrapper. The effective MTU of a face is determined by the link service.
+   */
+  ssize_t
+  getMtu() const;
+
   /** \return face state
    */
   FaceState
@@ -150,19 +168,6 @@
   time::steady_clock::TimePoint
   getExpirationTime() const;
 
-  /** \brief request the face to be closed
-   *
-   *  This operation is effective only if face is in UP or DOWN state,
-   *  otherwise it has no effect.
-   *  The face changes state to CLOSING, and performs cleanup procedure.
-   *  The state will be changed to CLOSED when cleanup is complete, which may
-   *  happen synchronously or asynchronously.
-   *
-   *  \warning the face must not be deallocated until its state changes to CLOSED
-   */
-  void
-  close();
-
   const FaceCounters&
   getCounters() const;
 
@@ -186,6 +191,12 @@
 }
 
 inline void
+Face::close()
+{
+  m_transport->close();
+}
+
+inline void
 Face::sendInterest(const Interest& interest, const EndpointId& endpointId)
 {
   m_service->sendInterest(interest, endpointId);
@@ -251,6 +262,12 @@
   return m_transport->getLinkType();
 }
 
+inline ssize_t
+Face::getMtu() const
+{
+  return m_service->getEffectiveMtu();
+}
+
 inline FaceState
 Face::getState() const
 {
@@ -263,12 +280,6 @@
   return m_transport->getExpirationTime();
 }
 
-inline void
-Face::close()
-{
-  m_transport->close();
-}
-
 inline const FaceCounters&
 Face::getCounters() const
 {
diff --git a/daemon/face/generic-link-service.cpp b/daemon/face/generic-link-service.cpp
index 7e32fc7..af03ffd 100644
--- a/daemon/face/generic-link-service.cpp
+++ b/daemon/face/generic-link-service.cpp
@@ -62,6 +62,25 @@
   m_reliability.setOptions(m_options.reliabilityOptions);
 }
 
+ssize_t
+GenericLinkService::getEffectiveMtu() const
+{
+  // Since MTU_UNLIMITED is negative, it will implicitly override any finite override MTU
+  return std::min(m_options.overrideMtu, getTransport()->getMtu());
+}
+
+bool
+GenericLinkService::canOverrideMtuTo(ssize_t mtu) const
+{
+  // Not allowed to override unlimited transport MTU
+  if (getTransport()->getMtu() == MTU_UNLIMITED) {
+    return false;
+  }
+
+  // Override MTU must be at least MIN_MTU (also implicitly forbids MTU_UNLIMITED and MTU_INVALID)
+  return mtu >= MIN_MTU;
+}
+
 void
 GenericLinkService::requestIdlePacket(const EndpointId& endpointId)
 {
@@ -74,7 +93,7 @@
 void
 GenericLinkService::sendLpPacket(lp::Packet&& pkt, const EndpointId& endpointId)
 {
-  const ssize_t mtu = this->getTransport()->getMtu();
+  const ssize_t mtu = getEffectiveMtu();
 
   if (m_options.reliabilityOptions.isEnabled) {
     m_reliability.piggyback(pkt, mtu);
@@ -169,7 +188,7 @@
 GenericLinkService::sendNetPacket(lp::Packet&& pkt, const EndpointId& endpointId, bool isInterest)
 {
   std::vector<lp::Packet> frags;
-  ssize_t mtu = this->getTransport()->getMtu();
+  ssize_t mtu = getEffectiveMtu();
 
   // Make space for feature fields in fragments
   if (m_options.reliabilityOptions.isEnabled && mtu != MTU_UNLIMITED) {
diff --git a/daemon/face/generic-link-service.hpp b/daemon/face/generic-link-service.hpp
index e30a3e6..38473f5 100644
--- a/daemon/face/generic-link-service.hpp
+++ b/daemon/face/generic-link-service.hpp
@@ -102,7 +102,6 @@
   class Options
   {
   public:
-    constexpr
     Options() noexcept
     {
     }
@@ -155,6 +154,16 @@
     /** \brief enables self-learning forwarding support
      */
     bool allowSelfLearning = true;
+
+    /** \brief overrides MTU provided by Transport
+     *
+     *  This MTU value will be used instead of the MTU provided by the transport if it is less than
+     *  the transport MTU. However, it will not be utilized when the transport MTU is unlimited.
+     *
+     *  Acceptable values for the override MTU are values >= MIN_MTU, which can be validated before
+     *  being set with canOverrideMtuTo().
+     */
+    ssize_t overrideMtu = std::numeric_limits<ssize_t>::max();
   };
 
   /** \brief counters provided by GenericLinkService
@@ -177,6 +186,16 @@
   const Counters&
   getCounters() const OVERRIDE_WITH_TESTS_ELSE_FINAL;
 
+  ssize_t
+  getEffectiveMtu() const OVERRIDE_WITH_TESTS_ELSE_FINAL;
+
+  /** \brief Whether MTU can be overridden to the specified value
+   *
+   *  If the transport MTU is unlimited, then this will always return false.
+   */
+  bool
+  canOverrideMtuTo(ssize_t mtu) const;
+
 PROTECTED_WITH_TESTS_ELSE_PRIVATE: // send path
   /** \brief request an IDLE packet to transmit pending service fields
    */
diff --git a/daemon/face/link-service.hpp b/daemon/face/link-service.hpp
index 415c185..fd35723 100644
--- a/daemon/face/link-service.hpp
+++ b/daemon/face/link-service.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -109,6 +109,9 @@
   virtual const Counters&
   getCounters() const;
 
+  virtual ssize_t
+  getEffectiveMtu() const;
+
 public: // upper interface to be used by forwarding
   /** \brief Send Interest to \p endpoint
    *  \pre setTransport has been called
@@ -225,6 +228,12 @@
   return *this;
 }
 
+inline ssize_t
+LinkService::getEffectiveMtu() const
+{
+  return m_transport->getMtu();
+}
+
 inline void
 LinkService::receivePacket(const Block& packet, const EndpointId& endpoint)
 {
diff --git a/daemon/face/transport.cpp b/daemon/face/transport.cpp
index 18d8608..6b235bc 100644
--- a/daemon/face/transport.cpp
+++ b/daemon/face/transport.cpp
@@ -31,8 +31,6 @@
 
 NFD_LOG_INIT(Transport);
 
-const ssize_t Transport::MIN_MTU;
-
 std::ostream&
 operator<<(std::ostream& os, TransportState state)
 {
diff --git a/daemon/face/transport.hpp b/daemon/face/transport.hpp
index 211fefc..d3840bc 100644
--- a/daemon/face/transport.hpp
+++ b/daemon/face/transport.hpp
@@ -339,13 +339,6 @@
   virtual void
   doSend(const Block& packet, const EndpointId& endpoint) = 0;
 
-public:
-  /** \brief minimum MTU that may be set on a transport
-   *
-   *  This is done to ensure the NDNLPv2 fragmentation feature functions properly.
-   */
-  static constexpr ssize_t MIN_MTU = 64;
-
 private:
   Face* m_face;
   LinkService* m_service;
diff --git a/daemon/face/udp-channel.cpp b/daemon/face/udp-channel.cpp
index 5a23758..4776661 100644
--- a/daemon/face/udp-channel.cpp
+++ b/daemon/face/udp-channel.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -180,9 +180,13 @@
     options.defaultCongestionThreshold = *params.defaultCongestionThreshold;
   }
 
+  if (params.mtu) {
+    options.overrideMtu = *params.mtu;
+  }
+
   auto linkService = make_unique<GenericLinkService>(options);
   auto transport = make_unique<UnicastUdpTransport>(std::move(socket), params.persistency,
-                                                    m_idleFaceTimeout, params.mtu);
+                                                    m_idleFaceTimeout);
   auto face = make_shared<Face>(std::move(linkService), std::move(transport));
 
   m_channelFaces[remoteEndpoint] = face;
diff --git a/daemon/face/udp-factory.cpp b/daemon/face/udp-factory.cpp
index 54b00b1..b15b762 100644
--- a/daemon/face/udp-factory.cpp
+++ b/daemon/face/udp-factory.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -268,10 +268,10 @@
     return;
   }
 
-  if (req.params.mtu && *req.params.mtu < Transport::MIN_MTU) {
+  if (req.params.mtu && *req.params.mtu < MIN_MTU) {
     // The specified MTU must be greater than the minimum possible
-    NFD_LOG_TRACE("createFace cannot create a face with MTU less than " << Transport::MIN_MTU);
-    onFailure(406, "MTU cannot be less than " + to_string(Transport::MIN_MTU));
+    NFD_LOG_TRACE("createFace: override MTU cannot be less than " << MIN_MTU);
+    onFailure(406, "Override MTU cannot be less than " + to_string(MIN_MTU));
     return;
   }
 
diff --git a/daemon/face/unicast-ethernet-transport.cpp b/daemon/face/unicast-ethernet-transport.cpp
index 97e5c4e..33e80bd 100644
--- a/daemon/face/unicast-ethernet-transport.cpp
+++ b/daemon/face/unicast-ethernet-transport.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -36,8 +36,7 @@
 UnicastEthernetTransport::UnicastEthernetTransport(const ndn::net::NetworkInterface& localEndpoint,
                                                    const ethernet::Address& remoteEndpoint,
                                                    ndn::nfd::FacePersistency persistency,
-                                                   time::nanoseconds idleTimeout,
-                                                   optional<ssize_t> overrideMtu)
+                                                   time::nanoseconds idleTimeout)
   : EthernetTransport(localEndpoint, remoteEndpoint)
   , m_idleTimeout(idleTimeout)
 {
@@ -46,13 +45,7 @@
   this->setScope(ndn::nfd::FACE_SCOPE_NON_LOCAL);
   this->setPersistency(persistency);
   this->setLinkType(ndn::nfd::LINK_TYPE_POINT_TO_POINT);
-
-  if (overrideMtu) {
-    this->setMtu(std::min<ssize_t>(localEndpoint.getMtu(), *overrideMtu));
-  }
-  else {
-    this->setMtu(localEndpoint.getMtu());
-  }
+  this->setMtu(localEndpoint.getMtu());
 
   NFD_LOG_FACE_DEBUG("Creating transport");
 
diff --git a/daemon/face/unicast-ethernet-transport.hpp b/daemon/face/unicast-ethernet-transport.hpp
index 63d74e9..49c9d48 100644
--- a/daemon/face/unicast-ethernet-transport.hpp
+++ b/daemon/face/unicast-ethernet-transport.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -43,8 +43,7 @@
   UnicastEthernetTransport(const ndn::net::NetworkInterface& localEndpoint,
                            const ethernet::Address& remoteEndpoint,
                            ndn::nfd::FacePersistency persistency,
-                           time::nanoseconds idleTimeout,
-                           optional<ssize_t> overrideMtu = {});
+                           time::nanoseconds idleTimeout);
 
 protected:
   bool
diff --git a/daemon/face/unicast-udp-transport.cpp b/daemon/face/unicast-udp-transport.cpp
index a81e1d0..140f691 100644
--- a/daemon/face/unicast-udp-transport.cpp
+++ b/daemon/face/unicast-udp-transport.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -41,8 +41,7 @@
 
 UnicastUdpTransport::UnicastUdpTransport(protocol::socket&& socket,
                                          ndn::nfd::FacePersistency persistency,
-                                         time::nanoseconds idleTimeout,
-                                         optional<ssize_t> overrideMtu)
+                                         time::nanoseconds idleTimeout)
   : DatagramTransport(std::move(socket))
   , m_idleTimeout(idleTimeout)
 {
@@ -51,14 +50,7 @@
   this->setScope(ndn::nfd::FACE_SCOPE_NON_LOCAL);
   this->setPersistency(persistency);
   this->setLinkType(ndn::nfd::LINK_TYPE_POINT_TO_POINT);
-
-  if (overrideMtu) {
-    this->setMtu(std::min(udp::computeMtu(m_socket.local_endpoint()), *overrideMtu));
-  }
-  else {
-    this->setMtu(udp::computeMtu(m_socket.local_endpoint()));
-  }
-  BOOST_ASSERT(this->getMtu() >= MIN_MTU);
+  this->setMtu(udp::computeMtu(m_socket.local_endpoint()));
 
   NFD_LOG_FACE_DEBUG("Creating transport");
 
diff --git a/daemon/face/unicast-udp-transport.hpp b/daemon/face/unicast-udp-transport.hpp
index fdadfb9..991d561 100644
--- a/daemon/face/unicast-udp-transport.hpp
+++ b/daemon/face/unicast-udp-transport.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -41,8 +41,7 @@
 public:
   UnicastUdpTransport(protocol::socket&& socket,
                       ndn::nfd::FacePersistency persistency,
-                      time::nanoseconds idleTimeout,
-                      optional<ssize_t> overrideMtu = {});
+                      time::nanoseconds idleTimeout);
 
 protected:
   bool
diff --git a/daemon/mgmt/face-manager.cpp b/daemon/mgmt/face-manager.cpp
index 9b36410..fd5f3aa 100644
--- a/daemon/mgmt/face-manager.cpp
+++ b/daemon/mgmt/face-manager.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -117,7 +117,8 @@
     faceParams.defaultCongestionThreshold = parameters.getDefaultCongestionThreshold();
   }
   if (parameters.hasMtu()) {
-    faceParams.mtu = parameters.getMtu();
+    // Cap this value at the maximum representable value in an ssize_t
+    faceParams.mtu = std::min<uint64_t>(std::numeric_limits<ssize_t>::max(), parameters.getMtu());
   }
   faceParams.wantLocalFields = parameters.hasFlagBit(ndn::nfd::BIT_LOCAL_FIELDS_ENABLED) &&
                                parameters.getFlagBit(ndn::nfd::BIT_LOCAL_FIELDS_ENABLED);
@@ -152,13 +153,10 @@
 static void
 copyMtu(const Face& face, T& to)
 {
-  auto transport = face.getTransport();
-  BOOST_ASSERT(transport != nullptr);
-
-  if (transport->getMtu() > 0) {
-    to.setMtu(std::min(static_cast<size_t>(transport->getMtu()), ndn::MAX_NDN_PACKET_SIZE));
+  if (face.getMtu() >= 0) {
+    to.setMtu(std::min<size_t>(face.getMtu(), ndn::MAX_NDN_PACKET_SIZE));
   }
-  else if (transport->getMtu() == face::MTU_UNLIMITED) {
+  else if (face.getMtu() == face::MTU_UNLIMITED) {
     to.setMtu(ndn::MAX_NDN_PACKET_SIZE);
   }
 }
diff --git a/tests/daemon/face/generic-link-service.t.cpp b/tests/daemon/face/generic-link-service.t.cpp
index e6b85d1..130c85e 100644
--- a/tests/daemon/face/generic-link-service.t.cpp
+++ b/tests/daemon/face/generic-link-service.t.cpp
@@ -132,6 +132,61 @@
   BOOST_CHECK(!data1pkt.has<lp::SequenceField>());
 }
 
+BOOST_AUTO_TEST_CASE(SendDataOverrideMtu)
+{
+  // Initialize with Options that disables all services and does not override MTU
+  GenericLinkService::Options options;
+  options.allowLocalFields = false;
+  initialize(options);
+
+  BOOST_CHECK_EQUAL(transport->getMtu(), MTU_UNLIMITED);
+  BOOST_CHECK_EQUAL(service->getEffectiveMtu(), MTU_UNLIMITED);
+  BOOST_CHECK_EQUAL(face->getMtu(), MTU_UNLIMITED);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MTU_UNLIMITED), false);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MTU_INVALID), false);
+  // Attempts to override MTU will fail when transport MTU is unlimited
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(4000), false);
+
+  // Initialize with Options that disables all services and overrides MTU (Transport MTU 8800)
+  options.overrideMtu = MIN_MTU;
+  initialize(options, ndn::MAX_NDN_PACKET_SIZE);
+
+  // Ensure effective MTU is override value
+  BOOST_CHECK_EQUAL(transport->getMtu(), ndn::MAX_NDN_PACKET_SIZE);
+  BOOST_CHECK_EQUAL(service->getEffectiveMtu(), MIN_MTU);
+  BOOST_CHECK_EQUAL(face->getMtu(), MIN_MTU);
+
+  // Check MTU overrides with Transport MTU finite
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MTU_UNLIMITED), false);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MTU_INVALID), false);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MIN_MTU - 1), false);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(MIN_MTU), true);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(4000), true);
+  BOOST_CHECK_EQUAL(service->canOverrideMtuTo(20000), true);
+
+  // Send Data with less than MIN_MTU octets
+  auto data1 = makeData("/localhost");
+  BOOST_CHECK_LE(data1->wireEncode().size(), MIN_MTU);
+  face->sendData(*data1, 0);
+
+  BOOST_CHECK_EQUAL(service->getCounters().nOutData, 1);
+  BOOST_CHECK_EQUAL(service->getCounters().nOutOverMtu, 0);
+
+  // Send Data with more than MIN_MTU octets
+  auto data2 = makeData("/localhost/test/1234567890/1234567890/1234567890/1234567890");
+  BOOST_CHECK_GT(data2->wireEncode().size(), MIN_MTU);
+  face->sendData(*data2, 0);
+
+  BOOST_CHECK_EQUAL(service->getCounters().nOutData, 2);
+  BOOST_CHECK_EQUAL(service->getCounters().nOutOverMtu, 1);
+
+  // Override MTU greater than the Transport's MTU will not be utilized
+  options.overrideMtu = 5000;
+  initialize(options, 4000);
+  BOOST_CHECK_EQUAL(service->getEffectiveMtu(), 4000);
+  BOOST_CHECK_EQUAL(face->getMtu(), 4000);
+}
+
 BOOST_AUTO_TEST_CASE(SendNack)
 {
   // Initialize with Options that disables all services
diff --git a/tests/daemon/face/lp-fragmenter.t.cpp b/tests/daemon/face/lp-fragmenter.t.cpp
index 9421619..7e38a62 100644
--- a/tests/daemon/face/lp-fragmenter.t.cpp
+++ b/tests/daemon/face/lp-fragmenter.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2020,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -76,7 +76,7 @@
 
 BOOST_AUTO_TEST_CASE(FragmentMultipleFragments)
 {
-  size_t mtu = Transport::MIN_MTU;
+  size_t mtu = MIN_MTU;
 
   lp::Packet packet;
   packet.add<lp::IncomingFaceIdField>(123);
@@ -156,7 +156,7 @@
 BOOST_AUTO_TEST_CASE(FragmentMtuTooSmall)
 {
   size_t mtu = 20;
-  BOOST_ASSERT(mtu < Transport::MIN_MTU);
+  BOOST_ASSERT(mtu < MIN_MTU);
 
   lp::Packet packet;
   packet.add<lp::IncomingFaceIdField>(123);
diff --git a/tests/daemon/face/lp-reliability.t.cpp b/tests/daemon/face/lp-reliability.t.cpp
index 9c14997..1880074 100644
--- a/tests/daemon/face/lp-reliability.t.cpp
+++ b/tests/daemon/face/lp-reliability.t.cpp
@@ -809,7 +809,7 @@
   // for Sequence and TxSequence, leaving 6 octets for piggybacking. Each Ack header is 12 octets,
   // so there's no room to piggyback any Ack in LpPacket.
 
-  transport->setMtu(Transport::MIN_MTU);
+  transport->setMtu(MIN_MTU);
 
   for (lp::Sequence i = 1000; i < 1100; i++) {
     reliability->m_ackQueue.push(i);