How to Change SD-WAN Packet Loss Priority from Low to High
Which configuration changes the packet loss priority from low to high?
Community Insight
The question tests whether you know PLP is only changed by a policer's exceed action, and the trap is selecting a match/classify clause because it merely names 'packet loss priority high'.
Cisco Catalyst SD-WAN sets every packet's packet loss priority (PLP) to low by default, so raising it to high requires a policer whose exceed action is remark rather than drop. The correct configuration is therefore the option that applies a policer with 'exceed remark' (option D), which re-marks excess traffic to PLP high for later congestion management.
Test-takers pick a configuration that matches or displays a PLP value (for example an option containing 'packet loss priority high' as a match term), because the phrase looks like a setting; matching PLP never changes it — only 'exceed remark' inside a policer does.
Community Discussion (12 comments)
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Expert Analysis
Why the Answer Is Correct
Option D is the configuration that applies a policer with the 'exceed remark' action, which is the documented mechanism for moving a packet from the default PLP low to PLP high. Cisco's localized data policy documentation states plainly that the drop action is equivalent to leaving PLP at low, while the remark action sets the PLP bit to high. Because PLP is a classification bit consumed later by QoS/queueing logic, only an actual remarking policer can flip it, which is exactly what option D does. The other three options do not contain an exceed-remark policer, so none of them re-marks traffic.Why the Other Options Are Wrong
Options A, B, and C at most reference packet loss priority inside a match or lookup context, which merely selects traffic already carrying a given PLP rather than rewriting it. A match clause on 'packet loss priority high' would discard all low-PLP packets, leaving the population unchanged — a classic classification-versus-action confusion. Only C and D are even plausible CLI forms, but C lacks the exceed remark keyword, so excess traffic would be dropped (implicitly PLP low) instead of re-marked. Without the policer's remark action, the PLP value stays at its default of low on every packet.Community Comment Notes
Commenters converge on D: daniccs8 summarized the mechanic as "Correct answer D. Apply a policer with exceed remark." and isaacmejia echoed that "By default, packets have a PLP value of low. To set the PLP value to high, apply a policer that includes the exceed remark option." Speirsington reinforced this by quoting Cisco's own wording that "The drop action is equivalent to setting the packet loss priority (PLP) bit to low." One caveat worth flagging: westh4m1234 suggested high PLP gives packets "a better chance to survive congestion," which reverses the intent — high PLP marks traffic as the first candidate for drop, not the last.Official Reference
Exam Strategy
On 300-415 policer questions, look for the action keywords (drop, exceed, remark, conform) rather than the traffic-matching keywords — actions change packet state, matches only select it. Remember the default states: conform rate, and PLP low unless a policer's exceed remark runs.
Frequently Asked Questions
Why can't a match clause on 'packet loss priority high' set PLP to high?
Matching only classifies packets that already carry that PLP value; it never rewrites bits. To change PLP you need an action, specifically a policer's exceed remark.
Does policer drop or exceed remark apply to PLP in Cisco SD-WAN?
Exceed drop leaves packets at the default PLP low (effectively dropping them), while exceed remark sets the PLP bit to high for subsequent QoS treatment.
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