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CoS Features and Limitations on MIC and MPC Interfaces


MIC and MPC interfaces on MX Series 5G Universal Routing Platforms use the Trio chipset-based queuing model, which supports CoS characteristics that are optimized compared to CoS characteristics supported by the standard queuing model. However, some CoS features are not supported or are supported with limitations on MIC and MPC interfaces.

When configuring CoS features on MIC and MPC interfaces on MX Series routers, keep the following limitations in mind.

Table 1: CoS Limitations on MIC and MPC Interfaces

CoS Feature

Limitation on MIC or MPC Interfaces


Interfaces on MPCs support up to 32 classifiers of each type per module.

BA classifier for MPLS packets

When you configure a behavior aggregate (BA) classifier that does not include a specific rewrite rule for MPLS packets, we highly recommend that you enable the default MPLS EXP classifier. Doing so ensures that MPLS exp value is rewritten according to the BA classifier rules configured for forwarding or packet loss priority. For more information, see Default MPLS EXP Classifier.

To enable the default MPLS EXP classifier, include the default statement at the [edit class-of-service interfaces interface-name unit logical-unit-number rewrite-rules exp] hierarchy level.

Rewrite rules

For interfaces on MPCs or on MICs installed in MPCs, you can figure up to 32 rewrite rules:

  • DSCP rewrite rules

  • Internet rewrite rules

  • EXP rewrite rules

  • IEEE rewrite rules

However, if you configure all 32 allowed rewrite rules, the class-of-service process can intermittently fail and generate syslog entries.

Default rewrite rules for MPLS-enabled interfaces

On interfaces other than MIC and MPC interfaces, the default EXP rewrite rule is automatically applied to MPLS-enabled interfaces, even if not configured. On MIC and MPC interfaces, you must explicitly configure EXP rewrite rules to MPLS-enabled interfaces.

Rewrite rules for service VLAN tag CoS bits

For MIC and MPC interfaces for VPLS or bridge domains, rewrite service VLAN tag CoS bits by configuring the rewrite rules on the core-facing interface.

Excess bandwidth sharing

Interfaces on MICs and MPCs do not support the excess-bandwidth-share configuration statement, which specifies how excess bandwidth at an interface set in a hierarchical scheduler environment is to be shared: proportionally or equally.

Instead, you can include the excess-rate statement at one of the following hierarchy levels:

Layer 1 and Layer 2 overhead

MIC and MPC interfaces take all Layer 1 and Layer 2 overhead bytes into account for all levels of the hierarchy, including preamble, interpacket gaps, frame check sequence, and cyclical redundancy check.

Queue statistics also take these overheads into account when displaying byte statistics.

Pairing of load-balancing links

When load balancing EQ MIC interfaces installed in Type 1 MPCs, you should configure odd- and even-numbered interfaces in the form interface-fpc/odd | even/ports. For example, if one link is xe-1/0/0, the other should be xe-1/1/0. If you do not configure odd and even load balancing, the system RED-drops packets when sending at line rate. This limitation does not apply to interfaces on EQ MICs installed in Type 2 MPCs.