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Understanding QoS Terminology and the Default QoS Strategy for the Barracuda CloudGen Firewall

Posted by Patrick Basso on Sep 26, 2018 2:58:53 PM

For part two of the QoS series: Barracuda created a metaphor for implementing QoS that is simple, straightforward and smooth. Let’s take a look.

Barracuda CloudGen Firewall


The Four Core Elements of QoS on the CloudGen Firewall are:

QoS Profile:

  • A QoS Profile is a named element that defines the template used to apply a QoS Policy to a physical interface
  • A QoS Profile includes a Virtual Tree
    • Constructed of one or more Virtual Interfaces
  • A QoS Profile has two independent traffic shaping rates
    • One Outbound rate (upload)
    • One Inbound rate (download)

Virtual Tree:

  • A Virtual Tree is a customizable set of one or more Virtual Interfaces
  • A Virtual Tree starts with a default Root Virtual Interface

Virtual Interface:

  • A Virtual Interface is hard coded with three classes/queues

Classes (Queues):

  • There are three Classes per Virtual Interface
  • Each Class has a forwarding rate and a drop capability which results in a statistical bandwidth allocation

QoS Strategy for Congestion Avoidance

Barracuda uses a Priority Queue and Weighted Random Early Detection (WRED)Today we are going to look at the Default QoS Profile. We are going to get started by looking at a special queue called the No Delay (Priority Queue) and the Default Root Virtual Interface which is made up of three regular queues.

There is (one) No Delay - Priority Queue

No Delay (Prioritized Traffic)

  • The priority queue is always serviced first. When a packet is forwarded the priority queue is always checked first for available packets.  If a packet exists in the priority queue, it is forwarded next.  If there are no packets in the priority queue, the packet scheduler looks to the regular queues next to forward a packet.

    • Warning: if the priority queue is always full, you have assigned too much traffic to this queue and it will consume 100% of the available bandwidth leaving nothing for the regular queues.

  • Care must be taken to understand the bandwidth needs of the Priority Queue.

 IMPORTANT NOTE: When congestion occurs, you must make sure that there is enough bandwidth to service the priority queue as well as the additional bandwidth needs of the other traffic queues or get a bigger pipe (more bandwidth).

There are (3) Regular Queues (aka: Classes). These 3 regular queues are part of the Default Root Virtual Interface and are defined as follows:

Class 1 – High Queue

Class 2 – Medium Queue

Class 3 – Low Queue

  • Each Regular Queue is assigned a forwarding weight

    • The number of packets to forward before dropping a packet

  • The weight for each of the three queues or classes can be customized to yield different statistical throughputs

Default QoS Profile Root Virtual Interface Weighting [10:2:1]

Traffic Class

Forwarded Packets

Drop Capability

Bandwidth Allocation

No Delay




Class 1


1 for every 10

~ 76%

Class 2


1 for every 2

~ 16%

Class 3


1 for 1

~ 08%

IMPORTANT NOTE: If a class is not being used, the bandwidth allocation is divided by the remaining classes with traffic.

 How to Go Further:

If you would like to learn more about the Barracuda CloudGen F-Series Firewall (formerly known as the NextGen Firewall) with guidance on how to get up and running faster, check out Fast Lane’s NextGen Firewall F – Foundation (NGF01) Course.  In this class, you will learn how to install, configure and maintain the features and functions of the CloudGen Firewall including QoS, high availability, central administration with the NextGen Control Center, and much more. 

 The goal of all Barracuda CloudGen Firewall classes is to learn how to fully protect your critical network resources and applications with Authorized Barracuda Training.  Fast Lane’s Barracuda CloudGen Firewall training is always hands-on and offers practical tips and problem-solving strategies for your network.

Topics: General, Barracuda, CloudGen, Firewall

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