Click the exhibit button below. At router PE1, customer packets are arriving tagged with a dotlp value of 6 and marked with a DSCP value of EF. Based on the configuration shown below for a VPLS…

Question

Exhibit

Options

• AThe DSCP value will be set to af21.
• BThe DSCP value will be set to af23.
• CThe DSCP value will remain as ef.
• DThe EXP value, in the MPLS headers, will be set to 4.
• EThe EXP value, in the MPLS headers, will be set to 3.

• A
  7% (2)
• B
  18% (5)
• C
  71% (20)
• D
  4% (1)

Explanation

In a VPLS service, the PE router provides transparent Layer 2 transport, meaning the customer's original IP packet - including its DSCP value of EF - is not remarked. The inner payload is preserved as-is, so C is correct. For the MPLS encapsulation, the ingress QoS policy classifies the packet using the dot1p value of 6, which maps (per the exhibited configuration) to an MPLS EXP value of 3, making E correct.

Why the distractors are wrong:

• A and B are wrong for the same reason - VPLS does not rewrite DSCP on customer packets; remarking DSCP (to af21 or af23) would violate the transparent L2 nature of the service.
• D is wrong because the dot1p-to-EXP mapping in the shown configuration resolves to 3, not 4; this is a deliberate distractor testing whether you know the specific policy mapping.

Memory tip: Think "VPLS = glass pipe for L2 - what goes in comes out unchanged at the IP layer." The only new marking added is the EXP in the MPLS header, which is derived from the dot1p (not the DSCP) at ingress - so always check the dot1p→EXP mapping table in the configuration, not the DSCP value.

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