Ericsson ECP-206 Exam With Confidence Using Practice Dumps

In the exhibit, router R4 is performing a swap action. This means that router R4 is replacing the incoming label with a new label and forwarding the packet to the next hop along the LSP. In this case, router R4 receives a packet with label 20 from router R3 and swaps it with label 30 before sending it to router R5.

The exhibit shows an example of an MPLS network with four routers: R1, R2, R3, and R4. Router R1 is the ingress PE router and router R4 is the egress PE router. Router R2 and R3 are P routers. Router R1 assigns label 10 to the packet and sends it to router R2. Router R2 swaps label 10 with label 20 and sends it to router R3. Router R3 swaps label 20 with label 30 and sends it to router R4. Router R4 removes label 30 from the packet and forwards it based on its IP header or another label in the stack.

Therefore, the answer is D.

References: MPLS Label Switching | MPLS Operation | Push, Swap,Push ⋆ IPCisco, A Complete Guide to Multiprotocol Label Switching (MPLS) - G2, Multiprotocol Label Switching - Wikipedia

Penultimate hop popping (PHP) is a function performed by certain routers in an MPLS enabled network. It refers to the process whereby the outermost label of an MPLS tagged packet is removed by a label switch router (LSR) before the packet is passed to an adjacent label edge router (LER). The purpose of PHP is to reduce the load on the LER, as it saves one cycle of label lookup. The LER can forward the packet based on its IP header or another label in the stack, without having to process the outer label. PHPfunctionality is achieved by the LER advertising a label with a value of 3 to its neighbors. This label is defined as "implicit-null" and informs the neighboring LSRs to perform PHP12.

References: Penultimate hop popping - Wikipedia, MPLS Penultimate hop popping - NetworkLessons.com

The function of LSR from an LDP perspective is to distribute labels of FEC to its LDP peers. LSR stands for Label Switching Router, which is a router that forwards packets based on labels rather than IP addresses in an MPLS network. LDP stands for Label Distribution Protocol, which is a protocol that distributes labels for MPLS forwarding along the shortest path calculated by an IGP. FEC stands for Forwarding Equivalence Class, which is a group of packets that are forwarded in the same manner by an LSR. An LSR uses LDP to advertise the label mappings for each FEC to its LDP peers, which are other LSRs that have established an LDP session with it12.

References: Ldp | Microsoft Learn, Label Distribution Protocol - Wikipedia