How is the underlay label managed in L3VPN data plane operations?

The correct answer is C. The label is swapped at each label-switching router in the service provider network. In an MPLS L3VPN, the ingress PE pushes both the VPN (inner) label and a transport (outer) label. Each MPLS LSR in the SP core examines the top (transport) label, swaps it for its next-hop label via its LFIB, and forwards the packet. Only the egress PE pops the transport label…

Layer 3 VPNs

Question

Options

AThe label is unchanged on provider routers and popped at the egress router.
BThe label is pushed at the provider edge router and popped at the next provider router.
CThe label is swapped at each label-switching router in the service provider network.
DThe label is pushed at the ingress LER and remains unchanged through the MPLS label swap

How the community answered

(59 responses)

A
5% (3)
B
3% (2)
C
90% (53)
D
2% (1)

Explanation

In an MPLS L3VPN, the ingress PE pushes both the VPN (inner) label and a transport (outer) label. Each MPLS LSR in the SP core examines the top (transport) label, swaps it for its next-hop label via its LFIB, and forwards the packet. Only the egress PE pops the transport label before delivering the packet to the CE.

Topics

#MPLS label operations#label swapping#LSR#L3VPN data plane

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