@@ -39,7 +39,8 @@ typedef enum {

     msg_del_block_dns,

     msg_register_dns,

     msg_enable_dhcp,

-    msg_register_ring_buffers

+    msg_register_ring_buffers,

+    msg_set_mtu

 } message_type_t;

 typedef struct {

@@ -127,4 +128,11 @@ typedef struct {

     HANDLE receive_tail_moved;

 } register_ring_buffers_message_t;

+typedef struct {

+    message_header_t header;

+    interface_t iface;

+    short family;

+    int mtu;

+} set_mtu_message_t;

+

 #endif /* ifndef OPENVPN_MSG_H_ */

@@ -73,6 +73,10 @@ static void netsh_ifconfig(const struct tuntap_options *to,

                            const in_addr_t netmask,

                            const unsigned int flags);

+static void windows_set_mtu(const int iface_index,

+                            const short family,

+                            const int mtu);

+

 static void netsh_set_dns6_servers(const struct in6_addr *addr_list,

                                    const int addr_len,

                                    const char *flex_name);

@@ -214,6 +218,47 @@ out:

     return ret;

 }

+static bool

+do_set_mtu_service(const struct tuntap *tt, const short family, const int mtu)

+{

+    DWORD len;

+    bool ret = false;

+    ack_message_t ack;

+    struct gc_arena gc = gc_new();

+    HANDLE pipe = tt->options.msg_channel;

+    const char *family_name = (family == AF_INET6) ? "IPv6" : "IPv4";

+    set_mtu_message_t mtu_msg = {

+        .header = {

+            msg_set_mtu,

+            sizeof(set_mtu_message_t),

+            0

+        },

+        .iface = {.index = tt->adapter_index,.name = tt->actual_name },

+        .mtu = mtu,

+        .family = family

+    };

+

+    if (!send_msg_iservice(pipe, &mtu_msg, sizeof(mtu_msg), &ack, "Set_mtu"))

+    {

+        goto out;

+    }

+

+    if (ack.error_number != NO_ERROR)

+    {

+        msg(M_NONFATAL, "TUN: setting %s mtu using service failed: %s [status=%u if_index=%d]",

+            family_name, strerror_win32(ack.error_number, &gc), ack.error_number, mtu_msg.iface.index);

+    }

+    else

+    {

+        msg(M_INFO, "%s MTU set to %d on interface %d using service", family_name, mtu, mtu_msg.iface.index);

+        ret = true;

+    }

+

+out:

+    gc_free(&gc);

+    return ret;

+}

+

 #endif /* ifdef _WIN32 */

 #ifdef TARGET_SOLARIS

@@ -1018,6 +1063,7 @@ do_ifconfig_ipv6(struct tuntap *tt, const char *ifname, int tun_mtu,

         do_address_service(true, AF_INET6, tt);

         add_route_connected_v6_net(tt, es);

         do_dns_service(true, AF_INET6, tt);

+        do_set_mtu_service(tt, AF_INET6, tun_mtu);

     }

     else

     {

@@ -1035,6 +1081,7 @@ do_ifconfig_ipv6(struct tuntap *tt, const char *ifname, int tun_mtu,

         add_route_connected_v6_net(tt, es);

         /* set ipv6 dns servers if any are specified */

         netsh_set_dns6_servers(tt->options.dns6, tt->options.dns6_len, ifname);

+        windows_set_mtu(tt->adapter_index, AF_INET6, tun_mtu);

     }

 #else /* platforms we have no IPv6 code for */

     msg(M_FATAL, "Sorry, but I don't know how to do IPv6 'ifconfig' commands on this operating system.  You should ifconfig your TUN/TAP device manually or use an --up script.");

@@ -1404,6 +1451,14 @@ do_ifconfig_ipv4(struct tuntap *tt, const char *ifname, int tun_mtu,

         netsh_ifconfig(&tt->options, ifname, tt->local,

                        tt->adapter_netmask, NI_IP_NETMASK|NI_OPTIONS);

     }

+    if (tt->options.msg_channel)

+    {

+        do_set_mtu_service(tt, AF_INET, tun_mtu);

+    }

+    else

+    {

+        windows_set_mtu(tt->adapter_index, AF_INET, tun_mtu);

+    }

 #else  /* if defined(TARGET_LINUX) */

     msg(M_FATAL, "Sorry, but I don't know how to do 'ifconfig' commands on this operating system.  You should ifconfig your TUN/TAP device manually or use an --up script.");

 #endif /* if defined(TARGET_LINUX) */

@@ -5432,6 +5487,40 @@ out:

     return ret;

 }

+static void

+windows_set_mtu(const int iface_index, const short family,

+                const int mtu)

+{

+    DWORD err = 0;

+    struct gc_arena gc = gc_new();

+    MIB_IPINTERFACE_ROW ipiface;

+    InitializeIpInterfaceEntry(&ipiface);

+    const char *family_name = (family == AF_INET6) ? "IPv6" : "IPv4";

+    ipiface.Family = family;

+    ipiface.InterfaceIndex = iface_index;

+    err = GetIpInterfaceEntry(&ipiface);

+    if (err == NO_ERROR)

+    {

+        if (family == AF_INET)

+        {

+            ipiface.SitePrefixLength = 0;

+        }

+        ipiface.NlMtu = mtu;

+        err = SetIpInterfaceEntry(&ipiface);

+    }

+

+    if (err != NO_ERROR)

+    {

+        msg(M_WARN, "TUN: Setting %s mtu failed: %s [status=%u if_index=%d]",

+            family_name, strerror_win32(err, &gc), err, iface_index);

+    }

+    else

+    {

+        msg(M_INFO, "Successfully set %s mtu on interface %d", family_name, iface_index);

+    }

+}

+

+

 /*

  * Return a TAP name for netsh commands.

  */

@@ -1286,6 +1286,29 @@ HandleRegisterRingBuffers(const register_ring_buffers_message_t *rrb, HANDLE ovp

     return err;

 }

+static DWORD

+HandleMTUMessage(const set_mtu_message_t *mtu)

+{

+    DWORD err = 0;

+    MIB_IPINTERFACE_ROW ipiface;

+    InitializeIpInterfaceEntry(&ipiface);

+    ipiface.Family = mtu->family;

+    ipiface.InterfaceIndex = mtu->iface.index;

+    err = GetIpInterfaceEntry(&ipiface);

+    if (err != NO_ERROR)

+    {

+        return err;

+    }

+    if (mtu->family == AF_INET)

+    {

+        ipiface.SitePrefixLength = 0;

+    }

+    ipiface.NlMtu = mtu->mtu;

+

+    err = SetIpInterfaceEntry(&ipiface);

+    return err;

+}

+

 static VOID

 HandleMessage(HANDLE pipe, HANDLE ovpn_proc, ring_buffer_handles_t *ring_buffer_handles,

               DWORD bytes, DWORD count, LPHANDLE events, undo_lists_t *lists)

@@ -1300,6 +1323,7 @@ HandleMessage(HANDLE pipe, HANDLE ovpn_proc, ring_buffer_handles_t *ring_buffer_

         dns_cfg_message_t dns;

         enable_dhcp_message_t dhcp;

         register_ring_buffers_message_t rrb;

+        set_mtu_message_t mtu;

     } msg;

     ack_message_t ack = {

         .header = {

@@ -1374,6 +1398,13 @@ HandleMessage(HANDLE pipe, HANDLE ovpn_proc, ring_buffer_handles_t *ring_buffer_

             }

             break;

+        case msg_set_mtu:

+            if (msg.header.size == sizeof(msg.mtu))

+            {

+                ack.error_number = HandleMTUMessage(&msg.mtu);

+            }

+            break;

+

         default:

             ack.error_number = ERROR_MESSAGE_TYPE;

             MsgToEventLog(MSG_FLAGS_ERROR, TEXT("Unknown message type %d"), msg.header.type);