QoS policy rules

You can create two rule types to define a QoS policy:

• Bandwidth limit provides bandwidth limitations on networks, ports or floating IPs. Any VM traffic that exceeds the specified rate will be dropped.
• Minimum bandwidth provides minimum bandwidth guarantees on networks, ports or floating IPs. VM traffic will use no less than the specified bandwidth.

Rules of different types can be combined in one QoS policy. For example, you can create a bandwidth limit rule and a minimum bandwidth rule. Additionally, you can add rules of one type to a policy if the traffic direction of each rule is different. For example, you can create two bandwidth limit rules, one for egress traffic and one for ingress traffic.

Limitations

• A QoS policy with minimum bandwidth cannot be applied to entire virtual networks.

To define a bandwidth limit

Specify the following parameters:

• max_kbps

  The maximum sustained transmission rate, in Kbps, allowed for the port.

  This value defines the long-term bandwidth limit. Under continuous traffic, the effective rate will not exceed this value.

• max_burst_kbps

  The maximum amount of data, in Kbits, that can be transmitted in a short burst when the token buffer is full. The buffer is replenished at the rate defined by max_kbps.

  Traffic can temporarily exceed the configured bandwidth limit while the buffer has available tokens. Once depleted, the rate is limited to max_kbps until the buffer is refilled.

  Under continuous high load, traffic effectively stays at max_kbps. Burst behavior improves responsiveness for short-lived or low-volume traffic (for example, web page loading or small file transfers) and is not intended for sustained throughput.

  • If the burst value is set too low, bandwidth usage will be throttled even with a proper bandwidth limit setting, resulting in a lower than expected bandwidth.
  • If the configured burst value is too high, too few packets could be limited, resulting in a higher than expected bandwidth limit.

  If you omit this parameter, the recommended burst value for TCP traffic will be applied, which defaults to 80% of the bandwidth limit. For example, if the bandwidth limit is 1000 kbps, then a burst value of 800 kbps is enough.

• ingress or egress

  The direction of traffic to which the rule applies:

  • ingress: Incoming traffic (download to the VM)
  • egress: Outgoing traffic (upload from the VM)

  Separate rules can be defined for each direction.

To define minimum bandwidth

Specify the following parameters:

• min-kbps

  The minimum guaranteed transmission rate, in Kbps, reserved for the port.

  This value ensures that the VM can achieve at least the specified bandwidth under network contention, provided sufficient resources are available on the host.

  Minimum bandwidth is enforced through resource reservation and scheduling mechanisms rather than traffic shaping.

• ingress or egress

  The direction of traffic to which the guarantee applies:

  • ingress: Incoming traffic (download to the VM)
  • egress: Outgoing traffic (upload from the VM)

  Separate guarantees can be defined for each direction.