IQ2 Class of Service

From Juniper Clue

IQ2 PIC Class of Service (CoS, aka Quality of Service, QoS) is a bit of a dark art due to gaps in the documentation. This page aims to document things that are not in the Juniper documentation or are but are written ambiguously.

• Multi-field classification with regular firewall filters happens after ingress scheduling. Simple filters allow classification before ingress scheduling but cannot match on DSCP values, although the JUNOS documentation does not mention this.

• A high priority queue is always implemented as strict-high, although the documentation reads as if a high priority queue is implemented as strict-high only when more than one medium-high, high, or strict-high scheduler is configured in a scheduler-map:

Gigabit Ethernet IQ2 PICs support only one queue in the scheduler map with medium-high, high, or strict-high priority. If more than one queue is configured with high or strict-high priority, the one that appears first in the configuration is implemented as strict-high priority. This queue receives unlimited transmission bandwidth. The remaining queues are implemented as low priority, which means they might be starved. (From Differences Between Gigabit Ethernet IQ and Gigabit Ethernet IQ2 PICs.)