Default MPLS EXP Classifier

Multiprotocol Label Switching (MPLS) class of service (CoS) works in conjunction with the routing device’s general CoS functionality.

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

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 transmission queues are serviced by configuring weighted round-robin, and to configure congestion avoidance using random early detection (RED).

For all PICs except PICs mounted on Juniper Networks M Series Multiservice Edge Router standard (nonenhanced) FPCs, if you enable the MPLS protocol family on a logical interface, the default MPLS EXP classifier is automatically applied to that logical interface.

Table 1 lists the default MPLS classifier mapping of EXP bits to forwarding classes and loss priorities..

Table 1: Default MPLS EXP Classification
MPLS EXP Bits	Forwarding Class	Loss Priority
`000`	`best-effort`	`low`
`001`	`best-effort`	`high`
`010`	`expedited-forwarding`	`low`
`011`	`expedited-forwarding`	`high`
`100`	`assured-forwarding`	`low`
`101`	`assured-forwarding`	`high`
`110`	`network-control`	`low`
`111`	`network-control`	`high`

Starting with Junos OS Release 21.1, PTX routers support two forwarding classes and four loss priorities for MPLS EXP default classification, as Table 2 shows.

Table 2: Default MPLS EXP Classification for PTX Routers
MPLS EXP Bits	Forwarding Class	Loss Priority
`000`	`best-effort`	`low`
`001`	`best-effort`	`high`
`010`	`best-effort`	`medium-low`
`011`	`best-effort`	`medium-high`
`100`	`network-control`	`medium-low`
`101`	`network-control`	`medium-high`
`110`	`network-control`	`low`
`111`	`network-control`	`high`

Default MPLS EXP Classifier

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