diff --git a/plugins/network/if1sec_ b/plugins/network/if1sec_
index fe07f4a9..a08cd906 100755
--- a/plugins/network/if1sec_
+++ b/plugins/network/if1sec_
@@ -7,38 +7,49 @@ cache="$MUNIN_PLUGSTATE/munin.$plugin.value"
 
 IFACE="${0##*/if1sec_}"         # interface
 
+if [ ! -r "/sys/class/net/$IFACE/statistics/tx_bytes" ]
+then
+	echo "# Unknown Interface : $IFACE"
+	exit 1
+fi
+
 if [ "$1" = "acquire" ]
 then
-	while sleep 1
-	do
-		echo $(
-			date +%s
-			cat /sys/class/net/$IFACE/statistics/tx_bytes
-			cat /sys/class/net/$IFACE/statistics/rx_bytes
-		)
-	done | awk "{
-			print \"${IFACE}_tx.value \" \$1 \":\" \$2;
-			print \"${IFACE}_rx.value \" \$1 \":\" \$3;
-		}" >> $cache &
+        (
+                while sleep 1
+                do
+                        echo $(
+                                date +%s
+                                cat /sys/class/net/$IFACE/statistics/tx_bytes
+                                cat /sys/class/net/$IFACE/statistics/rx_bytes
+                        )
+                done | awk "{
+                                print \"${IFACE}_tx.value \" \$1 \":\" \$2;
+                                print \"${IFACE}_rx.value \" \$1 \":\" \$3;
+                        }" >> $cache
+        ) &
         echo $! > $pidfile
-	exit 0
+        exit 0
 fi
 
 
 if [ "$1" = "config" ]
 then
-	cat <<EOF
+        cat <<EOF
 graph_title Interface 1sec stats for ${IFACE}
 graph_category 1sec::network
 graph_data_size custom 1d, 10s for 1w, 1m for 1t, 5m for 1y
 update_rate 1
+${IFACE}_tx.type DERIVE
+${IFACE}_tx.min 0
+${IFACE}_rx.type DERIVE
+${IFACE}_rx.min 0
 EOF
-	exit 0
+        exit 0
 fi
 
 # values
-cat ${FILE_VALUES}
-> ${FILE_VALUES}
+cat ${cache}
+> ${cache}
 
 exit 0
-