Configuring CoS for MPLS

When IP traffic enters a label-switched path (LSP) tunnel, the ingress router marks all packets with a class-of-service (CoS) value, which is used to place the traffic into a transmission priority queue. On the router, each interface has up to eight transmit queues. The CoS value is encoded as part of the Multiprotocol Label Switching (MPLS) header and remains in the packets until the MPLS header is removed when the packets exit from the egress router. The routers within the LSP utilize the CoS value set at the ingress router. The CoS value is encoded by means of the CoS bits (also known as the EXP or experimental bits).

MPLS class of service works in conjunction with the router's general CoS functionality. If you do not configure any CoS features, the default general CoS settings are used. For MPLS class of service, you might want to prioritize how the transmit queues are serviced by configuring weighted round-robin, and to configure congestion avoidance using random early detection (RED).

To configure CoS for MPLS, you can include the following statements at the [edit class-of-service] hierarchy level of the configuration:

If you do not specify a CoS value, the IP precedence bits from the packet's IP header are used as the packet's CoS value.

To specify a CoS value for packets in an LSP, include the class-of-service statement:

class-of-service cos-value;

You can include the class-of-service statement at the following hierarchy levels:

• [edit logical-routers logical-router-name protocols rsvp interface interface-name link-protection]
• [edit logical-routers logical-router-name protocols rsvp interface interface-name link-protection bypass destination]
• [edit logical-routers logical-router-name protocols mpls]
• [edit logical-routers logical-router-name protocols mpls label-switched-path path-name]
• [edit logical-routers logical-router-name protocols mpls label-switched-path path-name primary path-name]
• [edit logical-routers logical-router-name protocols mpls label-switched-path path-name secondary path-name]
• [edit logical-routers logical-router-name protocols mpls static-path prefix]
• [edit logical-routers logical-router-name protocols mpls interface interface-name label-map label-value]
• [edit protocols mpls]
• [edit protocols mpls interface interface-name label-map label-value]
• [edit protocols mpls label-switched-path path-name]
• [edit protocols mpls label-switched-path path-name primary path-name]
• [edit protocols mpls label-switched-path path-name secondary path-name]
• [edit protocols mpls static-path prefix]
• [edit protocols rsvp interface interface-name link-protection]
• [edit protocols rsvp interface interface-name link-protection bypass destination]

For more information, see the JUNOS MPLS Applications Configuration Guide.