JNCIA MPLS and VPNs 2

Question 1

In Junos L3VPN, what is the function of a Route Target (RT)?

Accepted Answer

Controls which VRFs import which VPNv4 routes, implementing the VPN topology (full-mesh, hub-spoke, extranet)

Answer

Route Targets are BGP extended communities that control VRF route import and export. A VRF exports routes with certain RT values; other VRFs import routes matching specific RT values, defining VPN connectivity topology.

Question 2

What is VPLS (Virtual Private LAN Service) in Junos?

Accepted Answer

A Layer 2 VPN service that provides multipoint Ethernet connectivity across an MPLS network, emulating a LAN switch for geographically dispersed sites

Answer

VPLS emulates a LAN (with MAC learning, flooding, and bridging) across an MPLS backbone, allowing multiple customer sites to appear as if they are connected to the same Ethernet switch.

Question 3

How does Junos implement MPLS traffic engineering (TE)?

Accepted Answer

Using RSVP-TE to signal LSPs with explicit routes and bandwidth reservations, with OSPF or IS-IS TE extensions advertising link bandwidth

Answer

Junos MPLS TE uses RSVP-TE for LSP signaling with constraint-based routing. OSPF-TE or IS-IS-TE extensions flood link attributes (bandwidth, TE metric, SRLG) that CSPF uses to compute explicit paths.

Question 4

What is 'fast reroute' (FRR) in Junos MPLS?

Accepted Answer

A protection mechanism that pre-computes backup paths for LSPs, enabling sub-50ms traffic rerouting upon link or node failure without waiting for IGP reconvergence

Answer

MPLS FRR pre-establishes detour or bypass LSPs before failures occur. When a protected link or node fails, traffic is immediately switched to the pre-computed backup path, typically within 50ms.

Question 5

In Junos, what command shows the MPLS label forwarding table?

Accepted Answer

show route table mpls.0

Answer

'show route table mpls.0' displays the MPLS label table (mpls.0 routing table) showing incoming labels, operations (pop/swap/push), and next-hops for each MPLS label binding.

JNCIA - Juniper Networks Certified Internet Associate Practice Test

JNCIA - Juniper Networks Certified Internet Associate Practice Test

JNCIA MPLS and VPNs 2