MPLS Fundamentals

DiffServ Tunneling Models

MPLS QoS Rule 4 causes an interesting behavior: Regardless of what the MPLS EXP value was changed to at the ingress LSR or any other LSR, that value is not copied to the exposed IP packet at the egress LSR of the MPLS network. In effect, this enables the operator of the MPLS cloud to carry the QoS value of the IP packet transparently through the MPLS network. No matter how many times the EXP bits are changed, by default, the IP precedence or DSCP bits of the IP packet are preserved; the value at the egress LSR is the same as when the IP packet entered the MPLS network. You can now tunnel the DiffServ value of the IP packet through the MPLS network (hence the name DiffServ Tunneling). The obvious advantage is that the ...