An election-office engineer packet-captures near an egress PE and notices the top transport label is already gone one hop before that PE. Which MPLS behavior most likely explains the missing top label?
Select an answer to reveal the explanation.
Short Explanation
PHP is the neighbor before the finish line tearing off the outer shipping label so the egress PE does not have to. Capture one hop early and the top label looks "missing" — that is often normal, not a broken LSP. Do not confuse it with CE tricks or QoS remarking deleting labels.
Full Explanation
Penultimate hop popping lets the router before the egress PE pop the outer transport label, so the egress PE receives an unlabeled IP packet or a remaining VPN label without an extra lookup on the transport label. Captures taken just upstream of egress therefore often show no top label even when the LSP is healthy. PHP is unrelated to CE ultimate-hop myths, blanket LDP failure, or EXP remarking. Account for PHP when interpreting near-egress label stacks.