QoS

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pfSense

HFSC burst is broken in pfSense. "It's a kernel issue with dummynet in pf."

HFSC General Information

If you put ack packets in a high bw queue, they will confirm with the remote system that data was received.

You can give certain services priority and keep speed and latency low.

You can serve x amount of data out quickly while slowing long term objects. You decide you want to serve out data quickly in the beginning of the connection and slow down after a few seconds. This is called a nonlinear service curve (NLSC or just SC).[1]

bandwidth

  • parent queue is max bandwidth on entire interface
  • child is percent or hard number that cannot exceed parent queue

priority level specifies the order in which a service is to occur relative to other queues and is used in CBQ and PRIQ, but not HFSC. Priority is does _not_ define an amount of bandwidth, but the order in which packets are buffered before being set out of the interface. Default (1)[2]

qlimit: the amount of packets to buffer and queue when the amount of available bandwidth has been exceeded. This value is 50 packets by default. When the total amount of upload bandwidth has been reached on the outgoing interface or higher queues are taking up all of the bandwidth then no more data can be sent. The qlimit will put the packets the queue can not send out into slots in memory in the order that they arrive. When bandwidth is available the qlimit slots will be emptied in the order they arrived; first in, first out (FIFO). If the qlimit reaches the maximum value of qlimit, the packets will be dropped.[3]

Look at qlimit slots as "emergency use only," but as a better alternative to dropping the packets out right. Understand dropping packets is the proper way TCP knows it needs to reduce bandwidth; so dropping packets are not bad. The problem is TCP Tahoe or Reno methods will slow down the connection too severely and it takes a while to ramp back up after a dropped packet. A small qlimit buffer helps smooth out the connection, but "buffer bloat" works against TCP's congestion control. Also, do not think that setting the qlimit really high will solve the problem of bandwidth starvation and packet drops. What you want to do is setup a queue with the proper bandwidth boundaries so that packets only go into the qlimit slots for a short time (no more than a second), if ever.[4]
  1. https://calomel.org/pf_hfsc.html
  2. https://calomel.org/pf_hfsc.html
  3. https://calomel.org/pf_hfsc.html
  4. https://calomel.org/pf_hfsc.html