QoS Script for VPN

[Lynx]

Here is my QoS script to deal with a VPN and apply QoS with correct overhead depending on whether the VPN is active or not:

admin@RT-AX86U-4168:/jffs/scripts# cat /jffs/configs/cake-qos.conf.add
DLIF='br0'
DLOPTIONS='wash dual-dsthost ingress'
ULIF_TUN='tun11'
TUN_PACKET_OVERHEAD='53'

admin@RT-AX86U-4168:/jffs/scripts# cat qos-start
#!/bin/sh

(
cat <<'ADDTEXT'
#!/bin/sh
source /etc/cake-qos.conf

OVERHEAD_TUN="overhead $(($(echo $OVERHEAD |grep -o -E '[0-9]+' |sed -n '1p')+TUN_PACKET_OVERHEAD)) mpu $(echo $OVERHEAD |grep -o -E '[0-9]+' |sed -n '2p')"

case "$1" in
start)
        if [[ -d /sys/class/net/"$ULIF_TUN" ]]; then
                tc qdisc add dev $ULIF_TUN root cake $ULPRIOQUEUE $ULOPTIONS $ULBW $OVERHEAD_TUN $FRAMING 2>/dev/null
                tc qdisc add dev $DLIF root cake $DLPRIOQUEUE $DLOPTIONS $DLBW $OVERHEAD_TUN $FRAMING 2>/dev/null
        else
                tc qdisc add dev $ULIF root cake $ULPRIOQUEUE $ULOPTIONS $ULBW $OVERHEAD $FRAMING 2>/dev/null
                tc qdisc add dev $DLIF root cake $DLPRIOQUEUE $DLOPTIONS $DLBW $OVERHEAD $FRAMING 2>/dev/null
        fi
        ;;
stop)
        tc qdisc del dev $ULIF root 2>/dev/null
        tc qdisc del dev $ULIF_TUN root 2>/dev/null
        tc qdisc del dev $DLIF root 2>/dev/null
        ;;
*)
esac
ADDTEXT
) > /tmp/qos

With $OVERHEAD set from the GUI as:

OVERHEAD='overhead 38 mpu 0'

This needs to be replaced by:

OVERHEAD='overhead {38+$TUN_PACKET_OVERHEAD} mpu 0'

The line:

OVERHEAD_TUN="overhead $(($(echo $OVERHEAD |grep -o -E '[0-9]+' |sed -n '1p')+TUN_PACKET_OVERHEAD)) mpu $(echo $OVERHEAD |grep -o -E '[0-9]+' |sed -n '2p')"

is a little ugly.
Is there a more efficient way to increment only the first integer by $TUN_PACKET_OVERHEAD?

 

[dave14305]

Fetch the overhead value directly from nvram.

nvram get qos_overhead

 

[Lynx]

I found a cool alternative solution:

OVERHEAD_TUN=$(echo $OVERHEAD | awk '$2=$2+'$TUN_OVERHEAD)

BTW any clue about the correct overhead to use for an LTE 4G connection? I just guessed 38 based on a standard Ethernet packet (without VLAN) which has 26 bytes of overhead and a 12 byte interpacket gap. The OpenWRT guys seem to suggest using '38' when determining the true overhead is highly uncertain.