350-501 MPLS and Segment Routing Practice Question
Exhibit
Refer to the exhibit. Router# show mpls ldp neighbor Peer LDP Ident: 192.168.1.2:0; Local LDP Ident: 192.168.1.1:0 TCP connection: 192.168.1.2.646 - 192.168.1.1.58370 State: Operacional; Msgs sent/rcvd: 342/341; Downstream Up time: 02:34:21 LDP discovery sources: GigabitEthernet0/0/0/0; Src IP addr: 192.168.1.2, transport address: 192.168.1.2 targeted-hello 192.168.1.2 -> 192.168.1.1 holdtime: 15 sec; proposed local/peer: 15/15 LDP id: 192.168.1.2:0
Refer to the exhibit. The show command output displays the LDP neighbor state. What does the 'Downstream' label mode indicate about label distribution?
⚠ Common exam trap
Cisco often tests the distinction between 'Downstream Unsolicited' and 'Downstream on Demand' modes, where candidates confuse the default DU behavior with the request-driven DoD behavior described in options B and C.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Labels are advertised to all neighbors without a request.
In the context of LDP, 'Downstream' label mode means that a router advertises label bindings for all prefixes in its routing table to its LDP neighbors without waiting for an explicit request. This is the default label distribution mode for LDP, where labels are proactively sent to all peers. Option D correctly identifies this behavior.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Labels are sent only to the peer that advertises the prefix.
Why it's wrong here
Downstream mode sends to all neighbors regardless of request.
- ✗
Labels are only distributed when explicitly requested.
Why it's wrong here
That describes Downstream-on-Demand.
- ✗
The neighbor must request labels via a Label Request message.
Why it's wrong here
That is downstream-on-demand.
- ✓
Labels are advertised to all neighbors without a request.
Why this is correct
Downstream mode means unsolicited label advertisement.
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