Traffic Control

This chapter covers some aspects related to traffic control, which is the core element to configure Quality of Service (QoS).

In order to process network traffic, three different objects can be combined: qdiscs, classes and filters:

  • A qdisc (traffic control on OSDx) is a traffic scheduler. E.g., FIFO (first-in first-out) is a common example of Qdisc.

  • Some qdiscs can contain classes, which can be seen as containers for further Qdiscs. These are called classful qdiscs. These objects are very useful because network traffic can be prioritized by specifying the classes that should be dequeued first.

  • Filters (match on OSDx) can be used to determine in which class a packet will be enqueued. They are always attached to classes.

Configuration

Currently, the following types of traffic control are supported:

  • fifo: the simplest traffic control. Pure first-in, first-out behavior. It can be limited in both packets and bytes. This is a classless qdisc.

  • fq-codel: fair queuing controlled delay uses a stochastic model to classify incoming packets into different flows. This traffic control provides a fair share of the bandwidth to all the flows. This is a classless qdisc.

  • network-emulator: this traffic control can be used to add or modify some network characteristics, such as delay, packet loss, duplication, etc. This is a classless qdisc.

  • tbf: token bucket filter is suited for slowing traffic down to a precisely configured rate. A different traffic control can be specified as a child for TBF. This is a classless qdisc.

  • htb: hierarchy token bucket implements a rich linksharing hierarchy of classes. HTB can prioritize classes and each class can contain a traffic control as a child. This is a classful qdisc.

  • wfq: weighted fair queuing is a network scheduling algorithm that allows specifying which fraction of the total capacity is given to each class, depending on their weight value. This qdisc can be offloaded to hardware on some devices. If hardware offload is not enabled, htb is used internally. This is a classful qdisc.

This is the syntax to create a traffic control:

set traffic control <qdisc_name> type <qdisc_type> [ ... ]

A traffic control discipline can be assigned to an interface. There are two modes: ingress and egress. The former one is used to control inbound traffic (in) and the latter to control outbound traffic (out).

In order to assign a traffic control to an interface, you have to use the following command:

set interfaces <if_type> <if_name> traffic control <in / out> <qdisc_name>

Tip

When it comes to testing bandwidth, the monitor test performance operational command turns out to be very handy.

Examples

Prioritizing traffic

Let’s suppose we want to set up a traffic control discipline in the egress hook of our eth0.

We want the following features:

  • Device bandwidth will be limited to 10 Mbps.

  • Three levels of priority that will be mapped to three different queues: gold queue (high priority, traffic with mark 99), silver queue (medium priority, vrfs SRV1 or SRV2) and bronze queue (low priority, unmatched traffic).

  • The gold queue will have an assured bandwidth of 50%; the silver queue 30%; and the bronze one 20%.

  • If there’s remaining bandwidth, it will be distributed among all queues.

On OSDx, we can achieve that by configuring the following commands:

set traffic control QoS type htb bandwidth 10
set traffic control QoS type htb class 1 bandwidth percentage 50
set traffic control QoS type htb class 1 priority 1
set traffic control QoS type htb class 2 bandwidth percentage 30
set traffic control QoS type htb class 2 priority 4
set traffic control QoS type htb class 3 bandwidth percentage 20
set traffic control QoS type htb class 3 priority 7
set traffic control QoS type htb match 1 class 1
set traffic control QoS type htb match 1 mark 99
set traffic control QoS type htb match 1 set tos 8
set traffic control QoS type htb match 2 class 2
set traffic control QoS type htb match 2 vrf-mark SRV1
set traffic control QoS type htb match 3 class 2
set traffic control QoS type htb match 3 vrf-mark SRV2
set traffic control QoS type htb default-class 3

Finally, to attach this traffic control to eth0, you have to use this command:

set interfaces ethernet eth0 traffic control out QoS

Limiting interface throughput

Now, let’s suppose we want to limit inbound traffic in eth1 to 512 Kbps. This can be easily done using a TBF traffic control.

In this case, we will configure a bucket size of 1875 bytes (0.015 mbit), this parameter should always be higher than device mtu.

To create the traffic control discipline, type the following commands:

set traffic control LIMITER type tbf bandwidth 0.512
set traffic control LIMITER type tbf burst 0.015
set traffic control LIMITER type tbf latency 1
set interfaces ethernet eth1 traffic control in LIMITER

In the case of TBF traffic control, we could also specify a child qdisc.

Example:

set traffic control FQ_LEAF type fq-codel
set traffic control LIMITER type tbf child-control FQ_LEAF

Here, you can find more examples related to traffic control disciplines.

Advanced features

It could be very useful to combine traffic policies and traffic control disciplines in some situations. Although there are many filters that can be used in a traffic control to classify network traffic (e.g., mark, TOS, etc), in some situations it may happen that you need to use more specialized ACLs (or traffic selectors).

Network packets can be marked using traffic policies and, depending on this value, enqueue packets in a specific traffic control class.

In addition to this, if we just need to limit traffic, we can use the traffic policy action rate-limit.

Example:

set traffic policy LIMITER rule 1 action rate-limit <rate> [burst <burst>]

That traffic policy will drop those packets that go over the rate-limit.

Here you can find more information about traffic policies.

Monitoring

The operational command traffic control show can be used to display statistics related to traffic control disciplines.

Example:

admin@osdx$ traffic control show
Traffic control for interface 'eth1' - 'ingress' mode

---------------------------------------------------------------------------
ID   traffic control    type    parent  bytes sent  pkts sent  pkts dropped
---------------------------------------------------------------------------
1:0  LIMITER          tbf       root        647202       9805          2369
2:0  FQ_LEAF          fq_codel  1:1         647202       9805          2369

Traffic control for interface 'eth0' - 'egress' mode

------------------------------------------------------------------------------------
ID   traffic control        type         parent  bytes sent  pkts sent  pkts dropped
------------------------------------------------------------------------------------
1:0  QoS              htb                root          1320         13             0
1:1  QoS              class 1            1:0            220          2             0
1:2  QoS              class 2            1:0            430          3             0
1:3  QoS              class 3 (default)  1:0            670          8             0

Command Summary

Configuration commands

Operational commands