Try to improve the documentation concerning the "tun" interface. Take note

that that kernel module must be loaded and IP forwarding enabled. Also add
slight improvements to the "tunconfig" script so that sudo /sbin/ifconfig
and sudo /sbin/iptables are really supported for current user if not root.

BasiliskII/README

@@ -442,6 +442,12 @@ ether <ethernet card description>
          instead of sending packets via physical media writes them to
          the user space program.
 
+         Prerequesties:
+         - Make sure the "tun" kernel module is loaded
+           # modprobe tun
+         - Make sure IP Fordwarding is enabled on your system
+           # echo 1 >/proc/sys/net/ipv4/ip_forward
+
          A virtual network configuration script is required and the
          default is /usr/local/BasiliskII/tunconfig unless you specify
          a different file with the "etherconfig" item.

BasiliskII/src/Unix/tunconfig

@@ -11,13 +11,23 @@
 # If the linux box is configured as a firewall, the rules below might
 # need some adjustments.
 #
+# The IP Tunnel driver requires IP forwarding to be enabled. Run as root:
+#
+#       echo 1 >/proc/sys/net/ipv4/ip_forward
+#
 ###########################################################################
 
 SUDO=/usr/bin/sudo
+IFCONFIG=/sbin/ifconfig
 IPTABLES=/sbin/iptables
 
 #########################################################
 
+[[ "x$1" = "x-n" ]] && {
+    DONT_EXECUTE=yes
+    shift 1
+}
+
 TUN_DEV=$1
 ACTION=$2
 
@@ -31,22 +41,35 @@ TUN_HOST=172.20.$NET_NUM.1
 #########################################################
 
 [[ $# = 2 ]] || {
-	echo "Usage: tunconfig iface up|down"
+	echo "Usage: tunconfig [-n] iface up|down"
     exit 2
 }
 
 [[ "`id -u`" = "0" ]] && {
-	echo "---> $SUDO not necessary." 1>&2
-	SUDO=""
+    echo "---> $SUDO not necessary." 1>&2
+    SUDO=""
 }
 
-[[ -x $IPTABLES ]] && {
-	IPTABLES="$SUDO $IPTABLES"
-} || {
+[[ -x $IPTABLES ]] || {
     echo "---> $IPTABLES not found." 1>&2
-	IPTABLES=/bin/true
+    exit 1
 }
 
+if [ -n "$SUDO" ]; then
+    $SUDO -l | grep -q "NOPASSWD: $IFCONFIG" || {
+        echo "---> Missing sudo NOPASSWD: $IFCONFIG." 1>&2
+        exit 1
+    }
+    $SUDO -l | grep -q "NOPASSWD: $IPTABLES" || {
+        echo "---> Missing sudo NOPASSWD: $IPTABLES." 1>&2
+        exit 1
+    }
+    IFCONFIG="$SUDO $IFCONFIG"
+    IPTABLES="$SUDO $IPTABLES"
+fi
+
+[[ "x$DONT_EXECUTE" = "xyes" ]] && exit 0
+
 $IPTABLES -L -n -t nat > /dev/null || exit 1
 
 #########################################################
@@ -62,7 +85,7 @@ $IPTABLES -L -n -t nat > /dev/null || exit 1
 #########################################################
 
 [[ "$ACTION" = down ]] && {
-    $SUDO /sbin/ifconfig $TUN_DEV down
+    $IFCONFIG $TUN_DEV down
 }
 
 #########################################################
@@ -70,7 +93,7 @@ $IPTABLES -L -n -t nat > /dev/null || exit 1
 #########################################################
 
 [[ "$ACTION" = up ]] && {
-    $SUDO /sbin/ifconfig $TUN_DEV $TUN_HOST
+    $IFCONFIG $TUN_DEV $TUN_HOST
 
     # masquerade the tun network
     $IPTABLES -t nat -A POSTROUTING -s $TUN_NET -d ! $TUN_NET -j MASQUERADE