350-501 · Question #39
Which two tasks must you perform when you implement LDP NSF on your network? (Choose two.)
The correct answer is B. Enable NSF for the link-state routing protocol that is in use on the network. E. Enable NSF for BGP. LDP Non-Stop Forwarding (NSF) allows LDP sessions to survive a Route Processor (RP) failover without dropping MPLS-forwarded traffic. For LDP NSF to function correctly, two conditions must be met: (1) the IGP (link-state routing protocol such as OSPF or IS-IS) must have NSF…
Question
Which two tasks must you perform when you implement LDP NSF on your network? (Choose two.)
Options
- AEnable NSF for EIGRP
- BEnable NSF for the link-state routing protocol that is in use on the network.
- CDisable Cisco Express Forwarding
- DImplement direct connections for LDP peers
- EEnable NSF for BGP
How the community answered
(36 responses)- A6% (2)
- B78% (28)
- C3% (1)
- D14% (5)
Explanation
LDP Non-Stop Forwarding (NSF) allows LDP sessions to survive a Route Processor (RP) failover without dropping MPLS-forwarded traffic. For LDP NSF to function correctly, two conditions must be met: (1) the IGP (link-state routing protocol such as OSPF or IS-IS) must have NSF enabled so it can maintain routing adjacencies through the RP switchover, providing stable next-hop information to LDP; and (2) BGP NSF must be enabled because BGP carries VPN and labeled route information that LDP depends on in MPLS VPN environments. CEF must remain enabled (not disabled), and direct connections or EIGRP NSF are not requirements for LDP NSF.
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