Policy-Based QOS Configuration

From ImageStream Router Documentation

Revision as of 21:50, 23 August 2010

The latest 4.4.0 and 4.2.12 distributions utilize an improved policy-based configuration for quality of service. The default rc.qos script has examples that use a new QoS library of functions, greatly simplifying QoS configuration.

Services define a type of traffic or service. Policies prioritize services, define how the traffic is queued and set minimum and maximum rates as a percentage of the maximum rate. Interface definitions apply a policy to an interface and define the maximum input and output rates as well as the maximum allowed latency for queued traffic. Because policy rates are specified using percentages a policy can be applied to multiple interfaces which may have differing input and output rates.

QOS_SERVICE

The QOS_SERVICE command defines parameters that match a type of service such as Web traffic or SMTP traffic. ImageStream pre-defines many services that can be added to or modified.

Currently only tc filter matches are supported. See the Linux Advanced Routing and Traffic Control guide for more information on tc filter matching.

Usage: QOS_SERVICE --name <service_name> [--init] --tc_match <tc_filter_command_match>

Example:

Create a new service called ims1 that matches traffic to and from 205.159.243.5

QOS_SERVICE --name ims1 --init --tc_match protocol ip u32 match ip src 205.159.243.5
QOS_SERVICE --name ims1 --tc_match protocol ip u32 match ip dst 205.159.243.5

Release 4.4.0-77 adds a new --host option to simplify the match above:

QOS_SERVICE --name ims1 --init --host 205.159.243.5

It is also possible to add on to a pre-defined service. Simply omit the '--init' option to add another match to a service.

Example:

In addition to the IP ToS bit matches also match on the SIP server's IP at 205.159.243.5.

QOS_SERVICE --name voip --tc-match protocol ip u32 match ip src 205.159.243.5
QOS_SERVICE --name voip --tc-match protocol ip u32 match ip dst 205.159.243.5

QOS_POLICY

The QOS_POLICY command prioritizes and rate-limits services. Low latency queueing and class-based queueing are supported.

Low latency queueing provides a strict priority-based first-in-first-out (FIFO) queue which does not rate shape the traffic. This queueing method is preferred for real-time traffic such as VoIP and routing protocols.

Priorities range from 0 to 9. Lower values indicate higher priority.

Minimum and maximum values are expressed as percentages ranging from 1 to 100. The actual rate will be calculated using this percentage and the interface's real bandwidth.

Class-based queueing provides prioritization but also performs rate shaping. This queueing method is preferred for non-realtime traffic such as Web and E-mail.

LLQ Usage: QOS_POLICY --name <policy_name> --type llq --service <service_name> --prio <priority 0-9> --max <max_percent>

Example:

QOS_POLICY --name default --type llq --service voip --prio 0 --max 90

CBQ Usage: QOS_POLICY --name <policy_name> --type cbq [--default | --service <service_name>] --prio <priority 0-9> --min <min_percent> --max <max_percent>

Example:

Set the default traffic class to priority 5 and prioritize TCP ACKs higher than other traffic.

QOS_POLICY --name default --type cbq --default --prio 5 --min 10 --max 75
QOS_POLICY --name default --type cbq --service ack --prio 3 --min 10 --max 40

QOS_IFACE

The QOS_IFACE command applies a policy to an interface. The maximum input and output rates are specified in Kbps (Kilobits per second). Latency is specified in milliseconds.

Fair queueing can also specified on the interface. ImageStream's PUFQ, standard fair-queueing and simple first-in-first-out (FIFO) queueing are options.

FIFO Usage: QOS_IFACE --name <interface_name> --policy <policy_name> --max_in <input_rate_in_Kbps> --max-out <output_rate_in_Kbps> --max-latency <max_latency_in_ms>

Example:

Assign the default policy to Ethernet0 which has a 3.0 Mbps input and 640 Kbps output rate. We want 150 ms max latency.

QOS_IFACE --name eth0 --policy default --max_in 3000 --max_out 640 --max_latency 150

Fair-Queueing Usage: QOS_IFACE --name <interface_name> --policy <policy_name> --max_in <input_rate_in_Kbps> --max-out <output_rate_in_Kbps> --max-latency <max_latency_in_ms> --fair_queue

sfq advanced options

Example:

Assign the default policy to Ethernet0 using fair queueing which has a 3.0 Mbps input and 640 Kbps output rate. We want 150 ms max latency.

QOS_IFACE --name eth0 --policy default --max_in 3000 --max_out 640 --max_latency 150 --fair_queue

PUFQ Usage: QOS_IFACE --name <interface_name> --policy <policy_name> --max_in <input_rate_in_Kbps> --max-out <output_rate_in_Kbps> --max-latency <max_latency_in_ms> --pufq --pufq_iface_type <inside | outside | nat_inside | nat_outside>

pufq advanced options

Example:

Assign the default policy to Ethernet0 using PUFQ which has a 3.0 Mbps input and 640 Kbps output rate. We want 150 ms max latency.

QOS_IFACE --name eth0 --policy default --max_in 3000 --max_out 640 --max_latency 150 --pufq --pufq_iface_type outside

ATM/DSL Adjustments

Starting in 4.4.0-72 and 4.2.12-46 a new --calc_atm parameter was added to the QOS_IFACE statement to allow the QOS subsystem to calculate ATM/AAL5 overhead for each packet being transmitted. This allows the system to specify the exact ATM data rate for the link.

Example:

A 3.0 Mb / 512 K DSL link has synced up at 3520000 bps down and 768000 bps up.

QOS_IFACE --name eth0 --policy default --max_in 3520 --max_out 768 --max_latency 150 --fair_queue --calc_atm

Frame Relay Parameters

frame relay options

Example:

A 256K CIR burstable to 384K Frame Relay circuit

QOS_IFACE --name Serial0.1 --policy default --max_latency 150 --fair_queue --frame_relay_mincir 256000 --frame_relay_cir 384000

Advanced Example

################################################################################
#
# Advanced example
# Override the voip service definition. We define voip as traffic to/from
# 192.168.0.35
# Policy:
#  Low Latency Queues:
#   voip: Low Latency Queue with highest priority and maximum of 90% of the
#         interface's bandwidth.
#  Class-Based Queues:
#   telnet: Highest priority with min of 10% and max 40%.
#   ssh: Lower priority than telnet with min 10% and max 40%.
#   tcp acks: Lower priority than ssh with min of 10% and max of 40%.
#   smtp: Lowest priority with min of 10% and max 60%.
#   default: Priority 5 (just above smtp) with min 10% max 95%
#
# Interface:
#  Apply the policy "default" to interface eth0 with the maximum input rate of
#  3000 Kbps (3.0 Mbps) and maximum output rate of 640 Kbps with a maximum
#  queueing latency of 150 ms. Configure PUFQ with nat_outside as the interface type
#  since this interface performs SNAT on user traffic.
#
QOS_SERVICE --name voip --init --tc_match protocol ip u32 match ip src 192.168.0.35/32
QOS_SERVICE --name voip        --tc_match protocol ip u32 match ip dst 192.168.0.35/32
QOS_POLICY --name default --type llq --service voip     --prio 0 --max 90
QOS_POLICY --name default --type cbq --init --default   --prio 5 --min 10 --max 95
QOS_POLICY --name default --type cbq --service telnet   --prio 1 --min 10 --max 40
QOS_POLICY --name default --type cbq --service ssh      --prio 2 --min 10 --max 40
QOS_POLICY --name default --type cbq --service ack      --prio 3 --min 10 --max 40
QOS_POLICY --name default --type cbq --service smtp     --prio 6 --min 10 --max 60

QOS_IFACE --name eth0 --policy default --max_in 3000 --max_out 640 --max_latency 150 --pufq --pufq_iface_type nat_outside