tc.sh

#!/bin/bash

# This script using tc (`man tc`) to shape egress traffic from a host to specific
# IP CIDR(s).

# RATES  Bandwidths  or  rates.  These parameters accept a floating point
# number, possibly followed by either a unit (both SI and IEC units supported),
# or a float followed by a '%' character to specify the rate as a percentage of
# the device's  speed  (e.g.  5%,  99.5%).  Warning:  specifying  the  rate as
# a percentage means a fraction of the current speed; if the speed changes, the
# value will not be recalculated.
#
#  default Bits per second
#
#  kbit    Kilobits per second
#
#  mbit    Megabits per second
#
#  gbit    Gigabits per second
#
#  tbit    Terabits per second
#
#  bps     Bytes per second
#
#  kbps    Kilobytes per second
#
#  mbps    Megabytes per second
#
#  gbps    Gigabytes per second
#
#  tbps    Terabytes per second
#

#
# Location of tc command
TC=/sbin/tc

# Network Interface (`ip a`) to shape.
IF=ens160

# Egress limit
PARENT_LIMIT=300kbit
BASE=10kbit
CEIL=300kbit

# CIDR ranges
# There should be 1 per target edge network
EDGE_0=192.168.201.1/32    # Edge Site 0 Description
EDGE_1=192.168.201.2/32    # Edge Site 1 Description
EDGE_2=192.168.201.3/32    # Edge Site 2 Description

# Filter options for limiting the intended interface.
U32="$TC filter add dev $IF protocol ip parent 1:0 prio 1 u32"

create () {
  echo "===> Setting up shaping"
  # Hierarchical Token Bucket (HTB) is used as it provides bandwidth-based shaping

  #   HTB    The Hierarchy Token Bucket implements a rich linksharing
  #   hierarchy of classes with an emphasis on conforming to existing
  #   practices. HTB facilitates guaranteeing bandwidth to classes, while
  #   also allowing specification of upper limits to inter-class sharing. It
  #   contains shaping elements, based on TBF and can prioritize classes.

  # root qdisc
  $TC qdisc add dev $IF root handle 1: htb default 30
  echo "===> Setup root qdisc on $IF"

  # classes
  # shapers of bandwidth
  #
  # These include parent and leaf (child) classes. A parent class can specify a limit
  # of bandwidth that can be borrowed by all children as they speed up from
  # their rate ($BASE) to their ceiling ($CEIL).
  #
  #                root 1: # root qdisc
  #                   |
  #                  /
  #                1:1 (parent class (overall QoS))
  #               /   \
  #            1:10  1:20 (leaf classes (individual QoS))
  #
  # In the above, a root qdisc (1:) is attached to an interface. Since rate limits
  # are not set on root, a new class is instantiated (1:1). This class is the
  # parent of all subsequent classes (1:10 and 1:20).
  #
  # With a rate on the parent (1:1) of 300mbits (the ceiling is the rate unless
  # otherwise specified). Each leaf can set their limit up to 300mbits. Each
  # child's rate ($BASE) is the starting rate. If 1:10 and 1:20 are transmitting
  # at maximum speed, assuming their ceilings are set to 300mbits, they will
  # each be throttled around 150mbits, since 150mbits * 2 = 300mbits.
  #
  #

  # parent class; it's ceiling (set implicitly by rate) is shared across leaves (children)
  $TC class add dev $IF parent 1: classid 1:1 htb rate $PARENT_LIMIT # parent

  # leaf classes; 1 per target CIDR.
  # ceil is the max upload speed this class should ever transmit.
  # rate is the starting upload speed; it should be much slower than ceiling
  $TC class add dev $IF parent 1:1 classid 1:10 htb rate $BASE ceil $CEIL # leaf
  $TC class add dev $IF parent 1:1 classid 1:20 htb rate $BASE ceil $CEIL # leaf
  $TC class add dev $IF parent 1:1 classid 1:30 htb rate $BASE ceil $CEIL # leaf
  echo "===> Setup child qdisc(s) on $IF"

  # filters for child classes
  # maps a destination IP with the appropriate (bandwidth limiting) class
  # flowid should map to a classid defined above
  $U32 match ip dst $EDGE_0 flowid 1:10
  $U32 match ip dst $EDGE_1 flowid 1:20
  $U32 match ip dst $EDGE_2 flowid 1:30
  echo "===> Setup filters"

  echo "===> Shaping configuration complete"
}

# clean removes *all* existing qdiscs from the target interface
clean () {
  echo "===> Deleting existing qdiscs on $IF"
  $TC qdisc del dev $IF root
  echo "===> Deleted existing qdiscs on $IF"
}

# run script; always clean then create
clean
create