300-420 · Question #79
In a simple MPLS L3VPN, which two tasks are performed by the PE router? (Choose two.)
The correct answer is C. It assigns labels to routes in individual VPNs. E. It exchanges VPNv4 or VPNv6 route with other PE routers. In an MPLS L3VPN, PE routers are responsible for assigning labels to routes within individual VPNs and exchanging these VPNv4/VPNv6 routes with other PE routers.
Question
In a simple MPLS L3VPN, which two tasks are performed by the PE router? (Choose two.)
Options
- AIt establishes pseudo wires with other PEs.
- BIt exchanges VPNv4 and VPNv6 routes with CE Devices.
- CIt assigns labels to routes in individual VPNs.
- DIt forwards labeled packets to CE devices.
- EIt exchanges VPNv4 or VPNv6 route with other PE routers.
How the community answered
(37 responses)- A5% (2)
- B3% (1)
- C92% (34)
Why each option
In an MPLS L3VPN, PE routers are responsible for assigning labels to routes within individual VPNs and exchanging these VPNv4/VPNv6 routes with other PE routers.
Pseudo wires are typically associated with Layer 2 VPNs (L2VPNs), not the core functionality of a simple MPLS L3VPN.
PE routers exchange standard IPv4 or IPv6 routes with CE devices, while VPNv4/VPNv6 routes are exchanged exclusively between PE routers.
PE routers assign a unique VPN label (also known as a service label or inner label) to each route learned from a connected CE device within a specific VPN. This label is critical for distinguishing traffic belonging to different VPNs as it traverses the MPLS backbone.
PE routers forward labeled packets *into* the MPLS core from CE devices and forward *unlabeled* packets *to* CE devices after stripping the MPLS labels.
PE routers establish BGP peering sessions with other PE routers (or a route reflector) to exchange VPNv4 or VPNv6 routes. These are standard IPv4 or IPv6 routes extended with a Route Distinguisher and the assigned VPN label, enabling inter-site VPN connectivity.
Concept tested: MPLS L3VPN PE router functions
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/15-mt/mp-l3-vpns-15-mt-book/mp-l3-vpns-cfg.html
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