diff --recursive --unified --new-file kernel-source-2.6.8/drivers/net/tun.c kernel-source-2.6.8-tunmtu/drivers/net/tun.c
--- kernel-source-2.6.8/drivers/net/tun.c	2004-08-14 07:36:57.000000000 +0200
+++ kernel-source-2.6.8-tunmtu/drivers/net/tun.c	2004-12-14 13:15:35.000000000 +0100
@@ -117,6 +117,14 @@
 	return &tun->stats;
 }
 
+static int tuntap_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if ((new_mtu < 68) || (new_mtu > 3000))
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 /* Initialize net device. */
 static void tun_net_init(struct net_device *dev)
 {
@@ -144,6 +152,7 @@
 		get_random_bytes(dev->dev_addr + sizeof(u16), 4);
 
 		ether_setup(dev);
+		dev->change_mtu = tuntap_change_mtu;
 		break;
 	}
 }