diff -ru linux-2.6.38/drivers/net/usb/cdc_ether.c linux-2.6.38.patched/drivers/net/usb/cdc_ether.c
--- linux-2.6.38/drivers/net/usb/cdc_ether.c	2011-03-15 02:20:32.000000000 +0100
+++ linux-2.6.38.patched/drivers/net/usb/cdc_ether.c	2011-06-30 18:48:29.749287600 +0200
@@ -86,6 +86,8 @@
 	struct usb_driver		*driver = driver_of(intf);
 	struct usb_cdc_mdlm_desc	*desc = NULL;
 	struct usb_cdc_mdlm_detail_desc *detail = NULL;
+	int				mapped_master;
+	int				mapped_slave;
 
 	if (sizeof dev->data < sizeof *info)
 		return -EDOM;
@@ -188,6 +190,24 @@
 						info->u->bMasterInterface0);
 			info->data = usb_ifnum_to_if(dev->udev,
 						info->u->bSlaveInterface0);
+			if ((!info->control || !info->data) 
+					&& (info->u->bMasterInterface0 > 0)) {
+				// try with mapping to start with 0
+				mapped_master = (info->u->bMasterInterface0 
+						- ((info->u->bSlaveInterface0 >
+						info->u->bMasterInterface0) ? 
+						info->u->bMasterInterface0 : 
+						info->u->bSlaveInterface0));
+				mapped_slave = (info->u->bSlaveInterface0 
+						- ((info->u->bSlaveInterface0 >
+						info->u->bMasterInterface0) ? 
+						info->u->bMasterInterface0 : 
+						info->u->bSlaveInterface0));
+				info->control = usb_ifnum_to_if(dev->udev,
+						mapped_master);
+				info->data = usb_ifnum_to_if(dev->udev,
+						mapped_slave);
+			}
 			if (!info->control || !info->data) {
 				dev_dbg(&intf->dev,
 					"master #%u/%p slave #%u/%p\n",