UE TUN MTU decreased to 1400

src/ue/app/task.cpp

@@ -202,7 +202,7 @@ void UeAppTask::setupTunInterface(const PduSession *pduSession)
 
     std::string ipAddress = utils::OctetStringToIp(pduSession->pduAddress->pduAddressInformation);
 
-    bool r = tun::TunConfigure(allocatedName, ipAddress, m_base->config->configureRouting, error);
+    bool r = tun::TunConfigure(allocatedName, ipAddress, cons::TunMtu, m_base->config->configureRouting, error);
     if (!r || error.length() > 0)
     {
         m_logger->err("TUN configuration failure [%s]", error.c_str());

src/ue/tun/config.cpp

@@ -109,7 +109,7 @@ static const char *NextInterfaceName(const std::string &prefix)
     return nullptr;
 }
 
-static void TunSetIpAndUp(const char *ifName, const char *ipAddr)
+static void TunSetIpAndUp(const char *ifName, const char *ipAddr, int mtu)
 {
     ifreq ifr{};
     memset(&ifr, 0, sizeof(struct ifreq));
@@ -133,14 +133,15 @@ static void TunSetIpAndUp(const char *ifName, const char *ipAddr)
     memcpy((((char *)&ifr + offsetof(struct ifreq, ifr_addr))), p, sizeof(struct sockaddr));
 
     if (ioctl(sockFd, SIOCSIFADDR, &ifr) < 0)
-    {
         throw LibError("ioctl(SIOCSIFADDR)", errno);
-    }
     if (ioctl(sockFd, SIOCGIFFLAGS, &ifr) < 0)
         throw LibError("ioctl(SIOCGIFFLAGS)", errno);
 
-    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
+    ifr.ifr_mtu = mtu;
+    if (ioctl(sockFd, SIOCSIFMTU, &ifr) < 0)
+        throw LibError("ioctl(SIOCSIFMTU)", errno);
 
+    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
     if (ioctl(sockFd, SIOCSIFFLAGS, &ifr) < 0)
         throw LibError("ioctl(SIOCSIFFLAGS)", errno);
 
@@ -349,12 +350,12 @@ int AllocateTun(const char *ifPrefix, char **allocatedName)
     return fd;
 }
 
-void ConfigureTun(const char *tunName, const char *ipAddr, bool configureRoute)
+void ConfigureTun(const char *tunName, const char *ipAddr, int mtu, bool configureRoute)
 {
     // acquire the configuration lock
     const std::lock_guard<std::mutex> lock(configMutex);
 
-    TunSetIpAndUp(tunName, ipAddr);
+    TunSetIpAndUp(tunName, ipAddr, mtu);
     if (configureRoute)
     {
         std::string table_name = ROUTING_TABLE_PREFIX + std::string(tunName);

src/ue/tun/config.hpp

@@ -16,6 +16,6 @@ namespace nr::ue::tun
 {
 
 int AllocateTun(const char *ifPrefix, char **allocatedName);
-void ConfigureTun(const char *tunName, const char *ipAddr, bool configureRoute);
+void ConfigureTun(const char *tunName, const char *ipAddr, int mtu, bool configureRoute);
 
 } // namespace nr::ue::tun

src/ue/tun/tun.cpp

@@ -32,11 +32,11 @@ int TunAllocate(const char *namePrefix, std::string &allocatedName, std::string
     return fd;
 }
 
-bool TunConfigure(const std::string &tunName, const std::string &ipAddress, bool configureRouting, std::string &error)
+bool TunConfigure(const std::string &tunName, const std::string &ipAddress, int mtu, bool configureRouting, std::string &error)
 {
     try
     {
-        tun::ConfigureTun(tunName.c_str(), ipAddress.c_str(), configureRouting);
+        tun::ConfigureTun(tunName.c_str(), ipAddress.c_str(), mtu, configureRouting);
     }
     catch (const LibError &e)
     {

src/ue/tun/tun.hpp

@@ -14,6 +14,6 @@ namespace nr::ue::tun
 {
 
 int TunAllocate(const char *namePrefix, std::string &allocatedName, std::string &error);
-bool TunConfigure(const std::string &tunName, const std::string &ipAddress, bool configureRouting, std::string &error);
+bool TunConfigure(const std::string &tunName, const std::string &ipAddress, int mtu, bool configureRouting, std::string &error);
 
 } // namespace nr::ue::tun
\ No newline at end of file

src/utils/constants.hpp

@@ -27,6 +27,7 @@ struct cons
 
     // TUN interface
     static constexpr const char *TunNamePrefix = "uesimtun";
+    static constexpr const int TunMtu = 1400;
 
     // Constraints
     static constexpr const int MinNodeName = 3;