diff --git a/examples/device/net_lwip_webserver/src/main.c b/examples/device/net_lwip_webserver/src/main.c
index 020f4e4d..27adce86 100644
--- a/examples/device/net_lwip_webserver/src/main.c
+++ b/examples/device/net_lwip_webserver/src/main.c
@@ -99,7 +99,7 @@ static err_t linkoutput_fn(struct netif *netif, struct pbuf *p)
     /* if the network driver can accept another packet, we make it happen */
     if (tud_network_can_xmit())
     {
-      tud_network_xmit(p);
+      tud_network_xmit(p, 0 /* unused for this example */);
       return ERR_OK;
     }
 
@@ -152,17 +152,49 @@ bool dns_query_proc(const char *name, ip_addr_t *addr)
   return false;
 }
 
-bool tud_network_recv_cb(struct pbuf *p)
+bool tud_network_recv_cb(const uint8_t *src, uint16_t size)
 {
   /* this shouldn't happen, but if we get another packet before 
   parsing the previous, we must signal our inability to accept it */
   if (received_frame) return false;
 
-  /* store away the pointer for service_traffic() to later handle */
-  received_frame = p;
+  if (size)
+  {
+    struct pbuf *p = pbuf_alloc(PBUF_RAW, size, PBUF_POOL);
+
+    if (p)
+    {
+      /* pbuf_alloc() has already initialized struct; all we need to do is copy the data */
+      memcpy(p->payload, src, size);
+
+      /* store away the pointer for service_traffic() to later handle */
+      received_frame = p;
+    }
+  }
+
   return true;
 }
 
+uint16_t tud_network_xmit_cb(uint8_t *dst, void *ref, uint16_t arg)
+{
+  struct pbuf *p = (struct pbuf *)ref;
+  struct pbuf *q;
+  uint16_t len = 0;
+
+  (void)arg; /* unused for this example */
+
+  /* traverse the "pbuf chain"; see ./lwip/src/core/pbuf.c for more info */
+  for(q = p; q != NULL; q = q->next)
+  {
+    memcpy(dst, (char *)q->payload, q->len);
+    dst += q->len;
+    len += q->len;
+    if (q->len == q->tot_len) break;
+  }
+
+  return len;
+}
+
 static void service_traffic(void)
 {
   /* handle any packet received by tud_network_recv_cb() */
diff --git a/src/class/net/net_device.c b/src/class/net/net_device.c
index 238d64d8..65fd1ab5 100644
--- a/src/class/net/net_device.c
+++ b/src/class/net/net_device.c
@@ -366,23 +366,7 @@ static void handle_incoming_packet(uint32_t len)
         }
   }
 
-  bool accepted = false;
-
-  if (size)
-  {
-    struct pbuf *p = pbuf_alloc(PBUF_RAW, size, PBUF_POOL);
-
-    if (p)
-    {
-      /* pbuf_alloc() has already initialized struct; all we need to do is copy the data */
-      memcpy(p->payload, pnt, size);
-      accepted = tud_network_recv_cb(p);
-
-      if (!accepted) pbuf_free(p);
-    }
-  }
-
-  if (!accepted)
+  if (!tud_network_recv_cb(pnt, size))
   {
     /* if a buffer was never handled by user code, we must renew on the user's behalf */
     tud_network_recv_renew();
@@ -429,9 +413,8 @@ bool tud_network_can_xmit(void)
   return can_xmit;
 }
 
-void tud_network_xmit(struct pbuf *p)
+void tud_network_xmit(void *ref, uint16_t arg)
 {
-  struct pbuf *q;
   uint8_t *data;
   uint16_t len;
 
@@ -441,14 +424,7 @@ void tud_network_xmit(struct pbuf *p)
   len = (_netd_itf.ecm_mode) ? 0 : CFG_TUD_NET_PACKET_PREFIX_LEN;
   data = transmitted + len;
 
-  /* traverse the "pbuf chain"; see ./lwip/src/core/pbuf.c for more info */
-  for(q = p; q != NULL; q = q->next)
-  {
-    memcpy(data, (char *)q->payload, q->len);
-    data += q->len;
-    len += q->len;
-    if (q->len == q->tot_len) break;
-  }
+  len += tud_network_xmit_cb(data, ref, arg);
 
   if (!_netd_itf.ecm_mode)
   {
diff --git a/src/class/net/net_device.h b/src/class/net/net_device.h
index 0175ea56..795b2f9e 100644
--- a/src/class/net/net_device.h
+++ b/src/class/net/net_device.h
@@ -32,15 +32,13 @@
 #include "device/usbd.h"
 #include "class/cdc/cdc.h"
 
-// TODO should not include external files
-#include "lwip/pbuf.h"
-#include "netif/ethernet.h"
-
 /* declared here, NOT in usb_descriptors.c, so that the driver can intelligently ZLP as needed */
 #define CFG_TUD_NET_ENDPOINT_SIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
 
 /* Maximum Tranmission Unit (in bytes) of the network, including Ethernet header */
-#define CFG_TUD_NET_MTU           (1500 + SIZEOF_ETH_HDR)
+#ifndef CFG_TUD_NET_MTU
+#define CFG_TUD_NET_MTU           1514
+#endif
 
 #ifdef __cplusplus
  extern "C" {
@@ -54,7 +52,10 @@
 void tud_network_init_cb(void);
 
 // client must provide this: return false if the packet buffer was not accepted
-bool tud_network_recv_cb(struct pbuf *p);
+bool tud_network_recv_cb(const uint8_t *src, uint16_t size);
+
+// client must provide this: copy from network stack packet pointer to dst
+uint16_t tud_network_xmit_cb(uint8_t *dst, void *ref, uint16_t arg);
 
 // client must provide this: 48-bit MAC address
 // TODO removed later since it is not part of tinyusb stack
@@ -67,7 +68,7 @@ void tud_network_recv_renew(void);
 bool tud_network_can_xmit(void);
 
 // if network_can_xmit() returns true, network_xmit() can be called once
-void tud_network_xmit(struct pbuf *p);
+void tud_network_xmit(void *ref, uint16_t arg);
 
 //--------------------------------------------------------------------+
 // INTERNAL USBD-CLASS DRIVER API