350-501 Question #395: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. The radio network and packet core are using the route RX-RZ-RB to establish communication. The LDP session between 10.10.10.5 and 10.10.10.1 is experiencing link flapping at random intervals for 30-45 seconds each time. A network engineer must protect the LDP session and improve MPLS traffic convergence. Which action meets these requirements?

Options

• AConfigure peer_acl_2 on RX and allow IP address 10.10.10.6 in LDP.
• BAttach peer_acl_1 in for session protection duration 1 on RX.
• CAdd session protection duration 60 for peer_acl_1 under the MPLS LDP instance on RZ.
• DEnable IGP-LDP sync on RZ and RX.

Explanation

The LDP session between RX and RZ is flapping for 30-45 seconds, requiring protection and improved MPLS convergence. Configuring LDP session protection with a duration greater than the flap interval (e.g., 60 seconds) will keep the LDP session and its labels active during the temporary outages, ensuring continuous MPLS traffic forwarding.

Common mistakes.

• A. Configuring an access list to allow an IP address in LDP is for controlling which peers can form LDP sessions, not for protecting an existing, flapping session.
• B. While the action type is correct, a session protection duration of 1 second is insufficient to protect against link flaps lasting 30-45 seconds.
• D. IGP-LDP synchronization is used to prevent traffic blackholing by delaying IGP route advertisement until LDP is fully operational on a link, not to protect an LDP session during link flaps.

Concept tested. LDP Session Protection configuration

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mpls/configuration/xe-3s/mp-xe-3s-book/mp-ldp-sess-prot.html

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