• DSCP rewrite on the PIC does not support distinct DSCP code-point rewrites if multiple forwarding classes (FC) are configured to map to the same queue in the “forwarding-class” configuration.
• The PIC can perform DSCP rewrite based on three PLP values, unlike four PLP values by the Packet Forwarding Engine.
• The protocol option is not supported in the following DSCP rewrite rule configuration:
  [edit class-of-service interfaces interface-name unit logical-unit-number]rewrite-rules {dscp (rewrite-name | <default>) protocol <protocol-types>;}

• The PIC has the ability to parse a packet with up to two VLAN tags. However, the following conditions apply when DSCP rewrite is enabled:

  • The PIC supports DSCP rewrite only for untagged and single VLAN tagged packets.
  • For DSCP rewrite in conjunction with VLAN rewrite push operations, the PIC can push only one tag if the packet is untagged.
  • If the packet has more than one VLAN tag (either because it was double tagged or because additional tags were pushed as part of a VLAN rewrite), then DSCP rewrite is not executed.

• Configuration of DSCP rewrite rules on the PIC overwrites the DSCP value coming from the Routing Engine for host-generated traffic. The behavior is as follows:

  • If the packet’s forwarding class and packet loss priority (PLP) match the DSCP rewrite rule on the PIC, then the DSCP code-point rewritten by the host-outbound-traffic statement is overwritten by the PIC’s DSCP rewrite with the corresponding DSCP code-point configured in the rewrite rule.
  • If the packet’s forwarding class and PLP do not match any DSCP rewrite rule on the PIC, then the DSCP code-point rewritten by the host-outbound-traffic statement is overwritten by the PIC’s DSCP rewrite as 6b’000000.
  This behavior is different from DSCP rewrites done in the Packet Forwarding Engine for other PICs. In those cases, the Packet Forwarding Engine processing is bypassed for host-generated packets and hence the DSCP set in the Routing Engine for host-generated packets is not overwritten in the Packet Forwarding Engine or PIC.
• If multiple forwarding classes map to the same queue, then the last forwarding class that maps to the same queue is picked and its code-point is used for DSCP rewrite.
• If both medium-high and medium-low PLP values are configured in the rewrite rule and if their rewrite code-points are different, then the code-point associated with medium-high is used for rewrite for both medium-high and medium-low packets on that logical interface. If only one of the PLP values (either medium-high or medium-low) is configured, then its corresponding code-point is used for rewrite for both medium-high and medium-low packets on that logical interface.

Note: A system error message can result if a configuration that conflicts with these limitations is committed or used .