Default MPLS EXP Classifier

MPLS CoS works with the routing device’s general CoS functionality.

When IP traffic enters a label-switched path (LSP) tunnel, the ingress device marks all packets with a 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 the egress routing device. The routing devices within the LSP utilize the CoS value set at the ingress device. The CoS value is encoded by means of the CoS bits (also known as the EXP bits).

If you do not configure any CoS features, Junos applies the default general CoS settings. For MPLS CoS, you might want to prioritize how the transmission queues are serviced by configuring weighted round-robin (WRR) and also configuring congestion avoidance using random early detection (RED).

If you enable the MPLS protocol family on a logical interface, Junos automatically applies the default MPLS EXP classifier 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

Related Documentation