In MPLS LDP (Label Distribution Protocol), label retention modes control how labels are stored in the Label Forwarding Information Base (LFIB).

DU Label Advertisement Mode (Downstream Unsolicited):

Labels are advertised to all LDP peers without a request.

The receiving router decides which label to use for forwarding.

Liberal vs. Conservative Label Retention:

Liberal Label Retention Mode (Correct Answer)

All received labels from all LDP peers are stored.

Even if a peer is not the optimal next hop, its label is retained.

Allows faster convergence during failures.

Conservative Label Retention Mode

Only the label from the best next-hop peer is stored.

Reduces memory usage but can slow down convergence in case of failure.

Reference from Huawei HCIE-Datacom Documentation:

Huawei MPLS LDP Configuration Guide -- Liberal vs. Conservative Label Retention

HCIE-Datacom Training Material -- Label Advertisement in MPLS Networks