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+.. _qos:
+
+##############
+Traffic Policy
+##############
+
+
+***
+QoS
+***
+
+The generic name of Quality of Service or Traffic Control involves
+things like shaping traffic, scheduling or dropping packets, which
+are the kind of things you may want to play with when you have, for
+instance, a bandwidth bottleneck in a link and you want to somehow
+prioritize some type of traffic over another.
+
+tc_ is a powerful tool for Traffic Control found at the Linux kernel.
+However, its configuration is often considered a cumbersome task.
+Fortunately, VyOS eases the job through its CLI, while using ``tc`` as
+backend.
+
+
+How to make it work
+===================
+
+In order to have VyOS Traffic Control working you need to follow 2
+steps:
+
+ 1. **Create a traffic policy**.
+
+ 2. **Apply the traffic policy to an interface ingress or egress**.
+    
+
+But before learning to configure your policy, we will warn you
+about the different units you can use and also show you what *classes*
+are and how they work, as some policies may require you to configure
+them.
+
+
+Units
+=====
+
+When configuring your traffic policy, you will have to set data rate
+values, watch out the units you are managing, it is easy to get confused
+with the different prefixes and suffixes you can use. VyOS will always
+show you the different units you can use.
+
+Prefixes
+--------
+
+They can be **decimal** prefixes.
+
+   .. code-block:: none
+
+	kbit  (10^3)    kilobit per second
+	mbit  (10^6)    megabit per second
+	gbit  (10^9)    gigabit per second
+ 	tbit  (10^12)   terabit per second
+	
+	kbps  (8*10^3)  kilobyte per second
+	mbps  (8*10^6)  megabyte per second
+	gbps  (8*10^9)  gigabyte per second
+	tbps  (8*10^12) terabyte per second
+
+Or **binary** prefixes.
+
+   .. code-block:: none
+
+	kibit (2^10 = 1024)    kibibit per second
+	mibit (2^20 = 1024^2)  mebibit per second
+	gibit (2^30 = 1024^3)  gibibit per second
+        tbit  (2^40 = 1024^4)  tebibit per second
+
+	kibps (1024*8)	       kibibyte (KiB) per second
+	mibps (1024^2*8)       mebibyte (MiB) per second
+        gibps (1024^3*8)       gibibyte (GiB) per second
+        tibps (1024^4*8)       tebibyte (TiB) per second
+
+
+Suffixes
+--------
+
+A *bit* is written as **bit**,
+   
+   .. code-block:: none
+
+        kbit (kilobits per second)
+        mbit (megabits per second)
+        gbit (gigabits per second)
+	tbit (terabits per second)
+
+while a *byte* is written as a single **b**.
+
+   .. code-block:: none
+
+        kbps (kilobytes per second)
+        mbps (megabytes per second)
+        gbps (gigabytes per second)
+
+
+
+
+.. _classes:
+
+Classes
+=======
+
+In the :ref:`creating_a_traffic_policy` section you will see that
+some of the policies use *classes*. Those policies let you distribute
+traffic into different classes according to different parameters you can
+choose. So, a class is just a specific type of traffic you select.
+
+The ultimate goal of classifying traffic is to give each class a
+different treatment.
+
+
+Matching traffic
+----------------
+
+In order to define which traffic goes into which class, you define
+filters (that is, the matching criteria). Packets go through these matching rules
+(as in the rules of a firewall) and, if a packet matches the filter, it
+is assigned to that class.
+
+In VyOS, a class is identified by a number you can choose when
+configuring it.
+
+
+.. note:: The meaning of the Class ID is not the same for every type of
+   policy. Normally policies just need a meaningless number to identify
+   a class (Class ID), but that does not apply to every policy.
+   The the number of a class in a Priority Queue it does not only
+   identify it, it also defines its priority.
+
+
+.. code-block:: none
+
+  set traffic-policy <policy> <policy-name> class <class-ID> match <class-matching-rule-name>
+
+
+In the command above, we set the type of policy we are going to
+work with and the name we choose for it; a class (so that we can
+differentiate some traffic) and an identifiable number for that class;
+then we configure a matching rule (or filter) and a name for it.
+
+A class can have multiple match filters:
+
+.. code-block:: none
+
+  set traffic-policy shaper MY-SHAPER class 30 match HTTP
+  set traffic-policy shaper MY-SHAPER class 30 match HTTPs
+
+A match filter can contain multiple criteria and will match traffic if
+all those criteria are true.
+
+For example:
+
+.. code-block:: none
+
+  set traffic-policy shaper MY-SHAPER class 30 match HTTP ip protocol tcp
+  set traffic-policy shaper MY-SHAPER class 30 match HTTP ip source port 80
+
+This will match TCP traffic with source port 80.
+
+There are many parameters you will be able to use in order to match the
+traffic you want for a class:
+
+ - **Ethernet (protocol, destination address or source address)**
+ - **Interface name**
+ - **IPv4 (DSCP value, maximum packet length, protocol, source address,**
+   **destination address, source port, destination port or TCP flags)**
+ - **IPv6 (DSCP value, maximum payload length, protocol, source address,**
+   **destination address, source port, destination port or TCP flags)**
+ - **Firewall mark**
+ - **VLAN ID**
+
+When configuring your filter, you can use the ``Tab`` key to see the many
+different parameters you can configure.
+
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy shaper MY-SHAPER class 30 match MY-FIRST-FILTER 
+   Possible completions:
+      description  Description for this match
+    > ether        Ethernet header match
+      interface    Interface name for this match
+    > ip           Match IP protocol header
+    > ipv6         Match IPV6 header
+      mark         Match on mark applied by firewall
+      vif          Virtual Local Area Network (VLAN) ID for this match
+ 
+ 
+
+As shown in the example above, one of the possibilities to match packets
+is based on marks done by the firewall, `that can give you a great deal of flexibility`_.
+
+You can also write a description for a filter:
+
+.. code-block:: none
+
+  set traffic-policy shaper MY-SHAPER class 30 match MY-FIRST-FILTER description "My filter description"
+
+
+
+.. note:: An IPv4 TCP filter will only match packets with an IPv4 header length of
+   20 bytes (which is the majority of IPv4 packets anyway).
+
+
+.. note:: IPv6 TCP filters will only match IPv6 packets with no header extension, see
+   https://en.wikipedia.org/wiki/IPv6_packet#Extension_headers
+
+
+Default
+-------
+
+Often you will also have to configure your *default* traffic in the same
+way you do with a class. *Default* can be considered a class as it
+behaves like that. It contains any traffic that did not match any
+of the defined classes, so it is like an open class, a class without
+matching filters.
+
+
+Class treatment
+---------------
+
+Once a class has a filter configured, you will also have to define what
+you want to do with the traffic of that class, what specific
+Traffic-Control treatment you want to give it. You will have different
+possibilities depending on the Traffic Policy you are configuring.
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy shaper MY-SHAPER class 30 
+   Possible completions:
+      bandwidth    Bandwidth used for this class
+      burst        Burst size for this class (default: 15kb)
+      ceiling      Bandwidth limit for this class
+      codel-quantum
+                   fq-codel - Number of bytes used as 'deficit' (default 1514)
+      description  Description for this traffic class
+      flows        fq-codel - Number of flows (default 1024)
+      interval     fq-codel - Interval (milliseconds) used to measure the delay (default 100)
+   +> match        Class matching rule name
+      priority     Priority for usage of excess bandwidth
+      queue-limit  Maximum queue size (packets)
+      queue-type   Queue type for this class
+      set-dscp     Change the Differentiated Services (DiffServ) field in the IP header
+      target       fq-codel - Acceptable minimum queue delay (milliseconds)
+   
+
+For instance, with :code:`set traffic-policy shaper MY-SHAPER class 30 set-dscp EF`
+you would be modifying the DSCP field value of packets in that class to
+Expedite Forwarding.
+
+
+  DSCP values as per :rfc:`2474` and :rfc:`4595`:
+
+  +---------+------------+--------+------------------------------+
+  | Binary  | Configured |  Drop  | Description                  |
+  | value   | value      |  rate  |                              |
+  +=========+============+========+==============================+
+  | 101110  |     46     |   -    | Expedited forwarding (EF)    |
+  +---------+------------+--------+------------------------------+
+  | 000000  |     0      |   -    | Best effort traffic, default |
+  +---------+------------+--------+------------------------------+
+  | 001010  |     10     | Low    | Assured Forwarding(AF) 11    |
+  +---------+------------+--------+------------------------------+
+  | 001100  |     12     | Medium | Assured Forwarding(AF) 12    |
+  +---------+------------+--------+------------------------------+
+  | 001110  |     14     | High   | Assured Forwarding(AF) 13    |
+  +---------+------------+--------+------------------------------+
+  | 010010  |     18     | Low    | Assured Forwarding(AF) 21    |
+  +---------+------------+--------+------------------------------+
+  | 010100  |     20     | Medium | Assured Forwarding(AF) 22    |
+  +---------+------------+--------+------------------------------+
+  | 010110  |     22     | High   | Assured Forwarding(AF) 23    |
+  +---------+------------+--------+------------------------------+
+  | 011010  |     26     | Low    | Assured Forwarding(AF) 31    |
+  +---------+------------+--------+------------------------------+
+  | 011100  |     28     | Medium | Assured Forwarding(AF) 32    |
+  +---------+------------+--------+------------------------------+
+  | 011110  |     30     | High   | Assured Forwarding(AF) 33    |
+  +---------+------------+--------+------------------------------+
+  | 100010  |     34     | Low    | Assured Forwarding(AF) 41    |
+  +---------+------------+--------+------------------------------+
+  | 100100  |     36     | Medium | Assured Forwarding(AF) 42    |
+  +---------+------------+--------+------------------------------+
+  | 100110  |     38     | High   | Assured Forwarding(AF) 43    |
+  +---------+------------+--------+------------------------------+
+
+
+
+
+.. _embed:
+
+Embedding one policy into another one
+-------------------------------------
+
+Often we need to embed one policy into another one. It is possible to do
+so on classful policies, by attaching a new policy into a class. For
+instance, you might want to apply different policies to the different
+classes of a Round-Robin policy you have configured.
+
+A common example is the case of some policies which, in order to be
+effective, they need to be applied to an interface that is directly
+connected where the bottleneck is. If your router is not
+directly connected to the bottleneck, but some hop before it, you can
+emulate the bottleneck by embedding your non-shaping policy into a
+classful shaping one so that it takes effect.
+
+You can configure a policy into a class through the ``queue-type``
+setting.
+
+.. code-block:: none
+
+   set traffic-policy shaper FQ-SHAPER bandwidth 4gbit
+   set traffic-policy shaper FQ-SHAPER default bandwidth 100%
+   set traffic-policy shaper FQ-SHAPER default queue-type fq-codel
+
+As shown in the last command of the example above, the `queue-type`
+setting allows these combinations. You will be able to use it
+in many policies.
+
+.. note:: Some policies already include other embedded policies inside.
+   That is the case of Shaper_: each of its classes use fair-queue
+   unless you change it.
+
+.. _creating_a_traffic_policy:
+
+
+Creating a traffic policy
+=========================
+
+VyOS lets you control traffic in many different ways, here we will cover
+every possibility. You can configure as many policies as you want, but
+you will only be able to apply one policy per interface and direction
+(inbound or outbound).
+
+Some policies can be combined, you will be able to embed_ a different
+policy that will be applied to a class of the main policy. 
+
+.. hint:: **If you are looking for a policy for your outbound traffic**
+   but you don't know which one you need and you don't want to go
+   through every possible policy shown here, **our bet is that highly
+   likely you are looking for a** Shaper_ **policy and you want to**
+   :ref:`set its queues <embed>` **as FQ-CoDel**.
+
+Drop Tail
+---------
+
+| **Queueing discipline:** PFIFO (Packet First In First Out).
+| **Applies to:** Outbound traffic.
+
+This the simplest queue possible you can apply to your traffic. Traffic
+must go through a finite queue before it is actually sent. You must
+define how many packets that queue can contain.
+
+When a packet is to be sent, it will have to go through that queue, so
+the packet will be placed at the tail of it. When the packet completely
+goes through it, it will be dequeued emptying its place in the queue and
+being eventually handed to the NIC to be actually sent out.
+
+Despite the Drop-Tail policy does not slow down packets, if many packets
+are to be sent, they could get dropped when trying to get enqueued at
+the tail. This can happen if the queue has still not been able to
+release enough packets from its head.
+
+This is the policy that requieres the lowest resources for the same
+amount of traffic. But **very likely you do not need it as you cannot
+get much from it. Sometimes it is used just to enable logging.**
+
+.. cfgcmd:: set traffic-policy drop-tail <policy-name> queue-limit <number-of-packets>
+
+   Use this command to configure a drop-tail policy (PFIFO). Choose a
+   unique name for this policy and the size of the queue by setting the
+   number of packets it can contain (maximum 4294967295).
+
+
+Fair Queue
+----------
+
+| **Queueing discipline:** SFQ (Stochastic Fairness Queuing).
+| **Applies to:** Outbound traffic.
+
+Fair Queue is a work-conserving scheduler which schedules the
+transmission of packets based on flows, that is, it balances traffic
+distributing it through different sub-queues in order to ensure
+fairness so that each flow is able to send data in turn, preventing any
+single one from drowning out the rest.
+
+
+.. cfgcmd:: set traffic-policy fair-queue <policy-name>
+
+   Use this command to create a Fair-Queue policy and give it a name.
+   It is based on the Stochastic Fairness Queueing and can be applied to
+   outbound traffic.
+
+In order to separate traffic, Fair Queue uses a classifier based on
+source address, destination address and source port. The algorithm
+enqueues packets to hash buckets based on those tree parameters.
+Each of these buckets should represent a unique flow. Because multiple
+flows may get hashed to the same bucket, the hashing algorithm is
+perturbed at configurable intervals so that the unfairness lasts only
+for a short while. Perturbation may however cause some inadvertent
+packet reordering to occur. An advisable value could be 10 seconds.
+
+One of the uses of Fair Queue might be the mitigation of Denial of
+Service attacks.
+
+.. cfgcmd:: set traffic-policy fair-queue <policy-name> hash-interval <seconds>`
+
+   Use this command to define a Fair-Queue policy, based on the
+   Stochastic Fairness Queueing, and set the number of seconds at which
+   a new queue algorithm perturbation will occur (maximum 4294967295).
+
+When dequeuing, each hash-bucket with data is queried in a round robin
+fashion. You can configure the length of the queue.
+
+.. cfgcmd:: set traffic-policy fair-queue <policy-name> queue-limit <limit>
+
+   Use this command to define a Fair-Queue policy, based on the
+   Stochastic Fairness Queueing, and set the number of maximum packets
+   allowed to wait in the queue. Any other packet will be dropped.
+
+.. note:: Fair Queue is a non-shaping (work-conserving) policy, so it
+   will only be useful if your outgoing interface is really full. If it
+   is not, VyOS will not own the queue and Fair Queue will have no
+   effect. If there is bandwidth available on the physical link, you can
+   embed_ Fair-Queue into a classful shaping policy to make sure it owns
+   the queue.
+
+
+
+.. _FQ-CoDel:
+
+FQ-CoDel
+--------
+
+| **Queueing discipline** Fair/Flow Queue CoDel.
+| **Applies to:** Outbound Traffic.
+
+The FQ-CoDel policy distributes the traffic into 1024 FIFO queues and
+tries to provide good service between all of them. It also tries to keep
+the length of all the queues short.
+
+FQ-CoDel fights bufferbloat and reduces latency without the need of
+complex configurations. It has become the new default Queueing
+Discipline for the interfaces of some GNU/Linux distributions.
+
+It uses a stochastic model to classify incoming packets into
+different flows and is used to provide a fair share of the bandwidth to
+all the flows using the queue. Each flow is managed by the CoDel
+queuing  discipline. Reordering within a flow is avoided since Codel
+internally uses a FIFO queue.
+
+FQ-CoDel is based on a modified Deficit Round Robin (DRR_) queue
+scheduler with the CoDel Active Queue Management (AQM) algorithm
+operating on each queue.
+
+
+.. note:: FQ-Codel is a non-shaping (work-conserving) policy, so it
+   will only be useful if your outgoing interface is really full. If it
+   is not, VyOS will not own the queue and FQ-Codel will have no
+   effect. If there is bandwidth available on the physical link, you can
+   embed_ FQ-Codel into a classful shaping policy to make sure it owns
+   the queue. If you are not sure if you need to embed your FQ-CoDel
+   policy into a Shaper, do it.
+
+
+FQ-CoDel is tuned to run ok with its default parameters at 10Gbit
+speeds. It might work ok too at other speeds without configuring
+anything, but here we will explain some cases when you might want to
+tune its parameters.
+
+When running it at 1Gbit and lower, you may want to reduce the
+`queue-limit` to 1000 packets or less. In rates like 10Mbit, you may
+want to set it to 600 packets.
+
+If you are using FQ-CoDel embedded into Shaper_ and you have large rates
+(100Mbit and above), you may consider increasing `quantum` to 8000 or
+higher so that the scheduler saves CPU.
+
+On low rates (below 40Mbit) you may want to tune `quantum` down to
+something like 300 bytes.
+
+At very low rates (below 3Mbit), besides tuning `quantum` (300 keeps
+being ok) you may also want to increase `target` to something like 15ms
+and increase `interval` to something around 150 ms.
+
+
+.. cfgcmd:: set traffic-policy fq-codel <policy name> codel-quantum <bytes>
+
+   Use this command to configure an fq-codel policy, set its name and
+   the maximum number of bytes (default: 1514) to be dequeued from a
+   queue at once.
+
+.. cfgcmd:: set traffic-policy fq-codel <policy name> flows <number-of-flows>
+
+   Use this command to configure an fq-codel policy, set its name and
+   the number of sub-queues (default: 1024) into which packets are
+   classified.
+
+.. cfgcmd:: set traffic-policy fq-codel <policy name> interval <miliseconds>
+
+   Use this command to configure an fq-codel policy, set its name and
+   the time period used by the control loop of CoDel to detect when a
+   persistent queue is developing, ensuring that the measured minimum
+   delay does not become too stale (default: 100ms).
+
+.. cfgcmd:: set traffic-policy fq-codel <policy-name> queue-limit <number-of-packets>`
+
+   Use this command to configure an fq-codel policy, set its name, and
+   define a hard limit on the real queue size. When this limit is
+   reached, new packets are dropped (default: 10240 packets).
+
+.. cfgcmd:: set traffic-policy fq-codel <policy-name> target <miliseconds>`
+
+   Use this command to configure an fq-codel policy, set its name, and
+   define the acceptable minimum standing/persistent queue delay. This
+   minimum delay is identified by tracking the local minimum queue delay
+   that packets experience (default: 5ms).
+
+
+Example
+^^^^^^^
+
+A simple example of an FQ-CoDel policy working inside a Shaper one.
+
+
+.. code-block:: none
+
+   set traffic-policy shaper FQ-CODEL-SHAPER bandwidth 2gbit
+   set traffic-policy shaper FQ-CODEL-SHAPER default bandwidth 100%
+   set traffic-policy shaper FQ-CODEL-SHAPER default queue-type fq-codel
+
+
+
+Limiter
+-------
+
+| **Queueing discipline:** Ingress policer.
+| **Applies to:** Inbound traffic.
+
+Limiter is one of those policies that uses classes_ (Ingress qdisc is
+actually a classless policy but filters do work in it).
+
+The limiter performs basic ingress policing of traffic flows. Multiple
+classes of traffic can be defined and traffic limits can be applied to
+each class. Although the policer uses a token bucket mechanism
+internally, it does not have the capability to delay a packet as a
+shaping mechanism does. Traffic exceeding the defined bandwidth limits
+is directly dropped. A maximum allowed burst can be configured too.
+
+You can configure classes (up to 4090) with different settings and a
+default policy which will be applied to any traffic not matching any of
+the configured classes.
+
+
+.. note:: In the case you want to apply some kind of **shaping** to your
+  **inbound** traffic, check the ingress-shaping_ section.
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> class <class ID> match <match-name> description <description>
+
+   Use this command to configure an Ingress Policer, defining its name,
+   a class identifier (1-4090), a class matching rule name and its
+   description.
+
+
+Once the matching rules are set for a class, you can start configuring
+how you want matching traffic to behave.
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> class <class-ID> bandwidth <rate>
+
+   Use this command to configure an Ingress Policer, defining its name,
+   a class identifier (1-4090) and the maximum allowed bandwidth for
+   this class.
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> class <class-ID> burst <burst-size>
+
+   Use this command to configure an Ingress Policer, defining its name,
+   a class identifier (1-4090) and the burst size in bytes for this
+   class (default: 15).
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> default bandwidth <rate>
+
+   Use this command to configure an Ingress Policer, defining its name
+   and the maximum allowed bandwidth for its default policy.
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> default burst <burst-size>
+
+   Use this command to configure an Ingress Policer, defining its name
+   and the burst size in bytes (default: 15) for its default policy.
+
+
+.. cfgcmd:: set traffic-policy limiter <policy-name> class <class ID> priority <value>
+
+   Use this command to configure an Ingress Policer, defining its name,
+   a class identifier (1-4090), and the priority (0-20, default 20) in
+   which the rule is evaluated (the lower the number, the higher the
+   priority).
+
+ 
+
+Network Emulator
+----------------
+
+| **Queueing discipline:** netem (Network Emulator) + TBF (Token Bucket Filter).
+| **Applies to:** Outbound traffic.
+
+VyOS Network Emulator policy emulates the conditions you can suffer in a
+real network. You will be able to configure things like rate, burst,
+delay, packet loss, packet corruption or packet reordering.
+
+This could be helpful if you want to test how an application behaves
+under certain network conditions.
+
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> bandwidth <rate>
+   
+   Use this command to configure the maximum rate at which traffic will
+   be shaped in a Network Emulator policy. Define the name of the policy
+   and the rate.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> burst <burst-size>
+   
+   Use this command to configure the burst size of the traffic in a
+   Network Emulator policy. Define the name of the Network Emulator
+   policy and its traffic burst size (it will be configured through the
+   Token Bucket Filter qdisc). Default:15kb. It will only take effect if
+   you have configured its bandwidth too.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> network-delay <delay>
+   
+   Use this command to configure a Network Emulator policy defining its
+   name and the fixed amount of time you want to add to all packet going
+   out of the interface. The latency will be added through the
+   Token Bucket Filter qdisc. It will only take effect if you have
+   configured its bandwidth too. You can use secs, ms and us. Default:
+   50ms.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> packet-corruption <percent>
+   
+   Use this command to emulate noise in a Network Emulator policy. Set
+   the policy name and the percentage of corrupted packets you want. A
+   random error will be introduced in a random position for the chosen
+   percent of packets.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> packet-loss <percent>`
+   
+   Use this command to emulate packet-loss conditions in a Network
+   Emulator policy. Set the policy name and the percentage of loss
+   packets your traffic will suffer.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> packet-reordering <percent>`
+   
+   Use this command to emulate packet-reordering conditions in a Network
+   Emulator policy. Set the policy name and the percentage of reordered
+   packets your traffic will suffer.
+
+.. cfgcmd:: set traffic-policy network-emulator <policy-name> queue-limit <limit>
+   
+   Use this command to define the length of the queue of your Network
+   Emulator policy. Set the policy name and the maximum number of
+   packets (1-4294967295) the queue may hold queued at a time.
+
+
+
+Priority Queue
+--------------
+
+| **Queueing discipline:** PRIO.
+| **Applies to:** Outbound traffic.
+
+
+The Priority Queue is a classful scheduling policy. It does not delay
+packets (Priority Queue is not a shaping policy), it simply dequeues
+packets according to their priority.
+
+.. note:: Priority Queue, as other non-shaping policies, is only useful
+   if your outgoing interface is really full. If it is not, VyOS will
+   not own the queue and Priority Queue will have no effect. If there is
+   bandwidth available on the physical link, you can embed_ Priority
+   Queue into a classful shaping policy to make sure it owns the queue.
+   In that case packets can be prioritized based on DSCP.
+
+Up to seven queues -defined as classes_ with different priorities- can
+be configured. Packets are placed into queues based on associated match
+criteria. Packets are transmitted from the queues in priority order. If
+classes with a higher priority are being filled with packets
+continuously, packets from lower priority classes will only be
+transmitted after traffic volume from higher priority classes decreases.
+
+
+.. note:: In Priority Queue we do not define clases with a meaningless
+   class ID number but with a class priority number (1-7). The lower the
+   number, the higher the priority.
+
+
+As with other policies, you can define different type of matching rules
+for your classes:
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy priority-queue MY-PRIO class 3 match MY-MATCH-RULE 
+   Possible completions:
+      description  Description for this match
+    > ether        Ethernet header match
+      interface    Interface name for this match
+    > ip           Match IP protocol header
+    > ipv6         Match IPV6 header
+      mark         Match on mark applied by firewall
+      vif          Virtual Local Area Network (VLAN) ID for this match
+
+
+As with other policies, you can embed_ other policies into the classes 
+(and default) of your Priority Queue policy through the ``queue-type``
+setting:
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy priority-queue MY-PRIO class 3 queue-type 
+   Possible completions:
+      fq-codel     Fair Queue Codel
+      fair-queue   Stochastic Fair Queue (SFQ)
+      drop-tail    First-In-First-Out (FIFO)
+      priority     Priority queueing based on DSCP
+      random-detect
+                   Random Early Detection (RED)
+
+
+.. cfgcmd:: set traffic-policy priority-queue <policy-name> class <class-ID>  queue-limit <limit>`
+
+   Use this command to configure a Priority Queue policy, set its name,
+   set a class with a priority from 1 to 7 and define a hard limit on
+   the real queue size. When this limit is reached, new packets are
+   dropped.
+
+
+
+.. _Random-Detect:
+
+Random-Detect
+-------------
+
+
+| **Queueing discipline:** Generalized Random Early Drop.
+| **Applies to:** Outbound traffic.
+
+A simple Random Early Detection (RED) policy would start randomly
+dropping packets from a queue before it reaches its queue limit thus
+avoiding congestion. That is good for TCP connections as the gradual
+dropping of packets acts as a signal for the sender to decrease its
+transmission rate.
+
+In contrast to simple RED, VyOS' Random-Detect uses a Generalized Random
+Early Detect policy that provides different virtual queues based on the
+IP Precedence value so that some virtual queues can drop more packets
+than others. 
+
+This is achieved by using the first three bits of the ToS (Type of
+Service) field to categorize data streams and, in accordance with the
+defined precedence parameters, a decision is made.
+
+IP precedence as defined in :rfc:`791`:
+
+ +------------+----------------------+
+ | Precedence |      Priority        |
+ +============+======================+
+ |      7     | Network Control      |
+ +------------+----------------------+
+ |      6     | Internetwork Control |
+ +------------+----------------------+
+ |      5     | CRITIC/ECP           |
+ +------------+----------------------+
+ |      4     | Flash Override       |
+ +------------+----------------------+
+ |      3     | Flash                |
+ +------------+----------------------+
+ |      2     | Immediate            |
+ +------------+----------------------+
+ |      1     | Priority             |
+ +------------+----------------------+
+ |      0     | Routine              |
+ +------------+----------------------+
+
+
+Random-Detect could be useful for heavy traffic. One use of this
+algorithm might be to prevent a backbone overload. But only for TCP
+(because dropped packets could be retransmitted), not for UDP.
+
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> bandwidth <bandwidth>
+
+   Use this command to configure a Random-Detect policy, set its name
+   and set the available bandwidth for this policy. It is used for
+   calculating the average queue size after some idle time. It should be
+   set to the bandwidth of your interface. Random Detect is not a
+   shaping policy, this command will not shape.
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> precedence <IP-precedence-value> average-packet <bytes>
+   
+   Use this command to configure a Random-Detect policy and set its
+   name, then state the IP Precedence for the virtual queue you are
+   configuring and what the size of its average-packet should be
+   (in bytes, default: 1024).
+
+.. note:: When configuring a Random-Detect policy: **the higher the
+   precedence number, the higher the priority**.
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> precedence <IP-precedence-value> mark-probability <value>
+   
+   Use this command to configure a Random-Detect policy and set its
+   name, then state the IP Precedence for the virtual queue you are
+   configuring and what its mark (drop) probability will be. Set the
+   probability by giving the N value of the fraction 1/N (default: 10).
+
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> precedence <IP-precedence-value> maximum-threshold <packets>
+   
+   Use this command to configure a Random-Detect policy and set its
+   name, then state the IP Precedence for the virtual queue you are
+   configuring and what its maximum threshold for random detection will
+   be (from 0 to 4096 packets, default: 18). At this size, the marking
+   (drop) probability is maximal.
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> precedence <IP-precedence-value> minimum-threshold <packets>
+   
+   Use this command to configure a Random-Detect policy and set its
+   name, then state the IP Precedence for the virtual queue you are
+   configuring and what its minimum threshold for random detection will
+   be (from 0 to 4096 packets).  If this value is exceeded, packets
+   start being eligible for being dropped.
+
+
+The default values for the minimum-threshold depend on IP precedence:
+
+ +------------+-----------------------+
+ | Precedence | default min-threshold |
+ +============+=======================+
+ |      7     |         16            |
+ +------------+-----------------------+
+ |      6     |         15            |
+ +------------+-----------------------+
+ |      5     |         14            |
+ +------------+-----------------------+
+ |      4     |         13            |
+ +------------+-----------------------+
+ |      3     |         12            |
+ +------------+-----------------------+
+ |      2     |         11            |
+ +------------+-----------------------+
+ |      1     |         10            |
+ +------------+-----------------------+
+ |      0     |          9            |
+ +------------+-----------------------+
+
+
+.. cfgcmd:: set traffic-policy random-detect <policy-name> precedence <IP-precedence-value> queue-limit <packets>
+   
+   Use this command to configure a Random-Detect policy and set its
+   name, then name the IP Precedence for the virtual queue you are
+   configuring and what the maximum size of its queue will be (from 1 to
+   1-4294967295 packets). Packets are dropped when the current queue
+   length reaches this value.
+
+
+If the average queue size is lower than the **min-threshold**, an
+arriving packet will be placed in the queue.
+
+In the case the average queue size is between **min-threshold** and
+**max-threshold**, then an arriving packet would be either dropped or
+placed in the queue, it will depend on the defined **mark-probability**.
+
+If the current queue size is larger than **queue-limit**,
+then packets will be dropped. The average queue size depends on its
+former average size and its current one.
+
+If **max-threshold** is set but **min-threshold is not, then
+**min-threshold** is scaled to 50% of **max-threshold**.
+
+In principle, values must be
+:code:`min-threshold` < :code:`max-threshold` < :code:`queue-limit`.
+
+
+
+
+Rate Control
+------------
+
+| **Queueing discipline:** Tocken Bucket Filter.
+| **Applies to:** Outbound traffic.
+
+Rate-Control is a classless policy that limits the packet flow to a set
+rate. It is a pure shaper, it does not schedule traffic. Traffic is
+filtered based on the expenditure of tokens. Tokens roughly correspond
+to bytes.
+
+Short bursts can be allowed to exceed the limit. On creation, the
+Rate-Control traffic is stocked with tokens which correspond to the
+amount of traffic that can be burst in one go. Tokens arrive at a steady
+rate, until the bucket is full.
+
+.. cfgcmd:: set traffic-policy rate-control <policy-name> bandwidth <rate>
+
+   Use this command to configure a Rate-Control policy, set its name
+   and the rate limit you want to have.
+
+.. cfgcmd:: set traffic-policy rate-control <policy-name> burst <burst-size>
+
+   Use this command to configure a Rate-Control policy, set its name
+   and the size of the bucket in bytes which will be available for
+   burst.
+
+
+As a reference: for 10mbit/s on Intel, you might need at least 10kbyte
+buffer if you want to reach your configured rate.
+
+A very small buffer will soon start dropping packets.
+
+.. cfgcmd:: set traffic-policy rate-control <policy-name> latency 
+
+   Use this command to configure a Rate-Control policy, set its name
+   and the maximum amount of time a packet can be queued (default: 50
+   ms).
+
+
+Rate-Control is a CPU-friendly policy. You might consider using it when
+you just simply want to slow traffic down.
+
+.. _DRR:
+
+Round Robin
+-----------
+
+| **Queueing discipline:** Deficit Round Robin.
+| **Applies to:** Outbound traffic.
+
+The round-robin policy is a classful scheduler that divides traffic in
+different classes_ you can configure (up to 4096). You can embed_ a
+new policy into each of those classes (default included).
+ 
+Each class is assigned a deficit counter (the number of bytes that a
+flow is allowed to transmit when it is its turn) initialized to quantum.
+Quantum is a parameter you configure which acts like a credit of fix
+bytes the counter receives on each round. Then the Round-Robin policy
+starts moving its Round Robin pointer through the queues. If the deficit
+counter is greater than the packet's size at the head of the queue, this
+packet will be sent and the value of the counter will be decremented by
+the packet size. Then, the size of the next packet will be compared to
+the counter value again, repeating the process. Once the queue is empty
+or the value of the counter is insufficient, the Round-Robin pointer
+will move to the next queue. If the queue is empty, the value of the
+deficit counter is reset to 0. 
+
+At every round, the deficit counter adds the quantum so that even large
+packets will have their opportunity to be dequeued.
+
+
+.. cfgcmd:: set traffic-policy round-robin <policy name> class
+   <class-ID> quantum <packets>
+
+   Use this command to configure a Round-Robin policy, set its name, set
+   a class ID, and the quantum for that class. The deficit counter will
+   add that value each round.
+
+.. cfgcmd:: set traffic-policy round-robin <policy name> class
+   <class ID> queue-limit <packets>
+
+   Use this command to configure a Round-Robin policy, set its name, set
+   a class ID, and the queue size in packets.
+
+As with other policies, Round-Robin can embed_ another policy into a
+class through the ``queue-type`` setting.
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy round-robin DRR class 10 queue-type 
+   Possible completions:
+      fq-codel     Fair Queue Codel
+      fair-queue   Stochastic Fair Queue (SFQ)
+      drop-tail    First-In-First-Out (FIFO)
+      priority     Priority queueing based on DSCP
+            
+
+
+
+.. _Shaper:
+
+Shaper
+------
+
+| **Queueing discipline:** Hierarchical Token Bucket.
+| **Applies to:** Outbound traffic.
+
+
+The Shaper policy does not guarantee a low delay, but it does guarantee
+bandwidth to different traffic classes and also lets you decide how to
+allocate more traffic once the guarantees are met.
+
+Each class can have a guaranteed part of the total bandwidth defined for
+the whole policy, so all those shares together should not be higher
+than the policy's whole bandwidth.
+
+If guaranteed traffic for a class is met and there is room for more
+traffic, the ceiling parameter can be used to set how much more
+bandwidth could be used. If guaranteed traffic is met and there are
+several classes willing to use their ceilings, the priority parameter
+will establish the order in which that additional traffic will be
+allocated. Priority can be any number from 0 to 7. The lower the number,
+the higher the priority.
+
+
+.. cfgcmd:: set traffic-policy shaper <policy-name> bandwidth <rate>
+
+   Use this command to configure a Shaper policy, set its name
+   and the maximum bandwidth for all combined traffic.
+
+
+.. cfgcmd:: set traffic-policy shaper <policy-name> class <class-ID> bandwidth <rate>
+
+   Use this command to configure a Shaper policy, set its name, define
+   a class and set the guaranteed traffic you want to allocate to that
+   class.
+
+.. cfgcmd:: set traffic-policy shaper <policy-name> class <class-ID> burst <bytes>
+
+   Use this command to configure a Shaper policy, set its name, define
+   a class and set the size of the `tocken bucket`_ in bytes, which will
+   be available to be sent at ceiling speed (default: 15Kb).
+
+.. cfgcmd:: set traffic-policy shaper <policy-name> class <class-ID> ceiling <bandwidth>
+
+   Use this command to configure a Shaper policy, set its name, define
+   a class and set the maximum speed possible for this class. The
+   default ceiling value is the bandwidth value.
+
+.. cfgcmd:: set traffic-policy shaper <policy-name> class <class-ID> priority <0-7>
+
+   Use this command to configure a Shaper policy, set its name, define
+   a class and set the priority for usage of available bandwidth once
+   guarantees have been met. The lower the priority number, the higher
+   the priority. The default priority value is 0, the highest priority.
+
+
+As with other policies, Shaper can embed_ other policies into its
+classes through the ``queue-type`` setting and then configure their
+parameters.
+
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy shaper HTB class 10 queue-type 
+   Possible completions:
+      fq-codel     Fair Queue Codel
+      fair-queue   Stochastic Fair Queue (SFQ)
+      drop-tail    First-In-First-Out (FIFO)
+      priority     Priority queueing based on DSCP
+      random-detect
+                   Random Early Detection (RED)
+
+
+.. code-block:: none
+
+   vyos@vyos# set traffic-policy shaper HTB class 10 
+   Possible completions:
+      bandwidth    Bandwidth used for this class
+      burst        Burst size for this class (default: 15kb)
+      ceiling      Bandwidth limit for this class
+      codel-quantum
+                   fq-codel - Number of bytes used as 'deficit' (default 1514)
+      description  Description for this traffic class
+      flows        fq-codel - Number of flows (default 1024)
+      interval     fq-codel - Interval (milliseconds) used to measure the delay (default 100)
+   +> match        Class matching rule name
+      priority     Priority for usage of excess bandwidth
+      queue-limit  Maximum queue size (packets)
+      queue-type   Queue type for this class
+      set-dscp     Change the Differentiated Services (DiffServ) field in the IP header
+      target       fq-codel - Acceptable minimum queue delay (milliseconds)
+
+
+
+.. note:: If you configure a class for **VoIP traffic**, don't give it any
+   *ceiling*, otherwise new VoIP calls could start when the link is
+   available and get suddenly dropped when other classes start using
+   their assigned *bandwidth* share.
+
+
+Example
+^^^^^^^
+
+A simple example of Shaper using priorities.
+
+
+.. code-block:: none
+
+   set traffic-policy shaper MY-HTB bandwidth '50mbit'
+   set traffic-policy shaper MY-HTB class 10 bandwidth '20%'
+   set traffic-policy shaper MY-HTB class 10 match DSCP ip dscp 'EF'
+   set traffic-policy shaper MY-HTB class 10 queue-type 'fq-codel'
+   set traffic-policy shaper MY-HTB class 20 bandwidth '10%'
+   set traffic-policy shaper MY-HTB class 20 ceiling '50%'
+   set traffic-policy shaper MY-HTB class 20 match PORT666 ip destination port '666'
+   set traffic-policy shaper MY-HTB class 20 priority '3'
+   set traffic-policy shaper MY-HTB class 20 queue-type 'fair-queue'
+   set traffic-policy shaper MY-HTB class 30 bandwidth '10%'
+   set traffic-policy shaper MY-HTB class 30 ceiling '50%'
+   set traffic-policy shaper MY-HTB class 30 match ADDRESS30 ip source address '192.168.30.0/24'
+   set traffic-policy shaper MY-HTB class 30 priority '5'
+   set traffic-policy shaper MY-HTB class 30 queue-type 'fair-queue'
+   set traffic-policy shaper MY-HTB default bandwidth '10%'
+   set traffic-policy shaper MY-HTB default ceiling '100%'
+   set traffic-policy shaper MY-HTB default priority '7'
+   set traffic-policy shaper MY-HTB default queue-type 'fair-queue'
+
+
+Applying a traffic policy
+=========================
+
+Once a traffic-policy is created, you can apply it to an interface:
+
+.. code-block:: none
+
+  set interfaces etherhet eth0 traffic-policy out WAN-OUT
+
+You can only apply one policy per interface and direction, but you could
+reuse a policy on different interfaces and directions:
+
+.. code-block:: none
+
+  set interfaces ethernet eth0 traffic-policy in WAN-IN
+  set interfaces etherhet eth0 traffic-policy out WAN-OUT
+  set interfaces etherhet eth1 traffic-policy in LAN-IN
+  set interfaces etherhet eth1 traffic-policy out LAN-OUT
+  set interfaces ethernet eth2 traffic-policy in LAN-IN
+  set interfaces ethernet eth2 traffic-policy out LAN-OUT
+  set interfaces etherhet eth3 traffic-policy in TWO-WAY-POLICY
+  set interfaces etherhet eth3 traffic-policy out TWO-WAY-POLICY
+  set interfaces etherhet eth4 traffic-policy in TWO-WAY-POLICY
+  set interfaces etherhet eth4 traffic-policy out TWO-WAY-POLICY
+
+Getting queueing information
+----------------------------
+
+.. opcmd:: show queueing <interface-type> <interface-name>
+
+   Use this command to see the queueing information for an interface.
+   You will be able to see a packet counter (Sent, Dropped, Overlimit
+   and Backlog) per policy and class configured.
+
+
+
+.. _ingress-shaping:
+
+The case of ingress shaping
+===========================
+
+| **Applies to:** Inbound traffic.
+
+For the ingress traffic of an interface, there is only one policy you
+can directly apply, a **Limiter** policy. You cannot apply a shaping
+policy directly to the ingress traffic of any interface because shaping
+only works for outbound traffic.
+
+This workaround lets you apply a shaping policy to the ingress traffic
+by first redirecting it to an in-between virtual interface
+(`Intermediate Functional Block`_). There, in that virtual interface,
+you will be able to apply any of the policies that work for outbound
+traffic, for instance, a shaping one.
+
+That is how it is possible to do the so-called "ingress shaping".
+
+
+.. code-block:: none
+
+   set traffic-policy shaper MY-INGRESS-SHAPING bandwidth 1000kbit
+   set traffic-policy shaper MY-INGRESS-SHAPING default bandwidth 1000kbit
+   set traffic-policy shaper MY-INGRESS-SHAPING default queue-type fair-queue
+   
+   set interfaces input ifb0 traffic-policy out MY-INGRESS-SHAPING
+   set interfaces ethernet eth0 redirect ifb0
+
+.. warning::
+
+  Do not configure IFB as the first step. First create everything else
+  of your traffic-policy, and then you can configure IFB.
+  Otherwise you might get the ``RTNETLINK answer: File exists`` error,
+  which can be solved with ``sudo ip link delete ifb0``.
+
+
+.. _that can give you a great deal of flexibility: https://blog.vyos.io/using-the-policy-route-and-packet-marking-for-custom-qos-matches
+.. _tc: https://en.wikipedia.org/wiki/Tc_(Linux)
+.. _tocken bucket: https://en.wikipedia.org/wiki/Token_bucket
+.. _HFSC: https://en.wikipedia.org/wiki/Hierarchical_fair-service_curve
+.. _Intermediate Functional Block: https://www.linuxfoundation.org/collaborate/workgroups/networking/ifb