An engineer enabled MPLS with 'mpls label protocol ldp' globally on all routers but no LDP neighbors appear. Which omission is the most likely cause?
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Correct answer: Missing 'mpls ip' command on the interfaces participating in MPLS..
Why this is the answer
The 'mpls ip' command is essential for enabling MPLS on specific interfaces. Without it, LDP (Label Distribution Protocol) cannot send or receive LDP hellos on those interfaces, preventing neighbor discovery and session establishment. While 'mpls label protocol ldp' enables LDP globally, it doesn't activate MPLS on individual interfaces. MP-BGP is used for VPNv4/v6 route distribution, not for basic LDP neighbor formation. LDP functions perfectly over IPv4; IPv6 support is an additional capability. Route distinguishers are used in MPLS VPNs to differentiate routes from different VPNs and do not directly impact LDP neighbor formation between core routers.
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