wondershaper (在同名的套件中) 的主要目的是最小化獨立網路負載的延遲。經由限制整體流量的值縮短連結的飽和值。

Once a network interface is configured, setting up this traffic limitation is achieved by running wondershaper interface download_rate upload_rate. The interface can be enp1s0, eth0 or ppp0 for example, and both rates are expressed in kilobits per second. The wondershaper remove interface command disables traffic control on the specified interface.

For an Ethernet connection, historically this script would be called right after the interface is configured. This is done by adding up and down directives to the /etc/network/interfaces file allowing declared commands to be run, respectively, after the interface is configured and before it is deconfigured. Or in the PPP case, creating a script that calls wondershaper in /etc/ppp/ip-up.d/ will enable traffic control as soon as the connection is up. Below is an example using this first method:

iface eth0 inet dhcp
    up /sbin/wondershaper eth0 500 100
    down /sbin/wondershaper remove eth0

Barring a specific QoS configuration, the Linux kernel uses the pfifo_fast queue scheduler, which provides a few interesting features by itself. The priority of each processed IP packet is based on the DSCP field (Differentiated Services Code Point) of this packet; modifying this 6-bit field is enough to take advantage of the scheduling features. Refer to https://en.wikipedia.org/wiki/Differentiated_services#Class_Selector for more information.

The DSCP field can be set by applications that generate IP packets, or modified on the fly by netfilter. The following rules are sufficient to increase responsiveness for a server's SSH service, note that the DSCP field must be set in hexadecimal:

nft add table ip mangle
nft add rule ip mangle PREROUTING tcp sport 22 counter ip dscp set 0x04
nft add rule ip mangle PREROUTING tcp dport 22 counter ip dscp set 0x04