In an MPLS VPN environment, the QoS marking over the MPLS backbone must be different from the one that is received from the customer.
The forwarding on the egress PE is based on the marking that is set by the ingress PE.
Which null label and QoS mode can achieve this?
Click on the arrows to vote for the correct answerA. B. C. D. E. F.
A.http://www.cisco.com/en/US/tech/tk828/technologies_q_and_a_item09186a00800a43f5.shtml#wp27379 http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_te_diffserv/configuration/15-mt/mp-te-diffserv-15-mt-book/mp-diffserv-tun-mode.pdf https://ccdewiki.wordpress.com/2013/05/31/three-qos-models-in-mpls/
In an MPLS VPN environment, it is important to maintain the Quality of Service (QoS) for the traffic traversing the MPLS backbone while ensuring that the customer's QoS markings are not propagated beyond the provider's network. Therefore, the QoS marking over the MPLS backbone must be different from the one that is received from the customer.
To achieve this, the provider edge (PE) routers use a technique known as MPLS QoS uniform mode, which changes the QoS markings of the packets to a default value, as the packets enter the MPLS backbone. This ensures that the customer's QoS markings are not propagated beyond the MPLS network.
Furthermore, the forwarding on the egress PE is based on the QoS marking that is set by the ingress PE. When an ingress PE router receives a packet from a customer, it assigns a QoS label to the packet based on the customer's QoS policy. This QoS label is then used by the egress PE router to forward the packet to the appropriate egress interface based on the egress interface's QoS policy.
To implement this approach, the MPLS null label is used to indicate that the packet is not associated with any particular label. There are two types of MPLS null labels: explicit and implicit.
The explicit null label is used to explicitly indicate that the next hop for the packet is the egress PE router, and the packet should not be assigned any MPLS label. On the other hand, the implicit null label is used to indicate that the label stack is empty, and the packet should be forwarded based on the IP header alone.
In the context of MPLS QoS, the MPLS explicit null label is used to indicate that the packet should be forwarded based on the QoS label assigned by the ingress PE router. The MPLS implicit null label is not used for QoS forwarding, as it does not carry any QoS information.
In addition, there are two modes of MPLS QoS: uniform and short pipe. In uniform mode, the QoS label is the same for all packets, regardless of their source or destination. In short pipe mode, the QoS label is based on the egress interface's QoS policy.
Therefore, based on the above explanation, the correct answer to the question is:
D. MPLS explicit null with uniform mode.