Restrictions and Cautions for CoS Configuration on Services Interfaces

The following restrictions and cautions apply to CoS configuration on services interfaces:

• The adaptive services interface does not support scheduling, only DiffServ marking and queue assignment. You must configure scheduling at the [edit class-of-service] hierarchy level on the output interface or fabric.
• In the default configuration, queues 1 and 2 receive 0 percent bandwidth. If packets will be assigned to these queues, you must configure a scheduling map.
• You must issue a commit full command before using custom forwarding-class names in the configuration.
• Only the JUNOS standard DiffServ names can be used in the configuration. Custom names are not recognized.

• On M-series routers, you can configure rewrite rules that change packet headers and attach the rules to output interfaces. These rules might overwrite the DSCP marking configured on an AS or MultiServices PIC. It is important to keep this adverse effect in mind and use care when creating system-wide configurations.

  For example, knowing that the AS or MultiServices PIC can mark packets with any ToS or DSCP value and the output interface is restricted to only eight DSCP values, rewrite rules on the output interface condense the mapping from 64 to 8 values with overall loss of granularity. In this case, you have the following options:

  • Remove the rewrite rules from the output interface.
  • Configure the output interface to include the most important mappings.