350-501 MPLS and Segment Routing Practice Question
Which BGP extended community is used to signal the OSPF domain ID between PE routers in an MPLS L3VPN when OSPF is the PE-CE protocol?
⚠ Common exam trap
Cisco often tests the confusion between the OSPF Domain ID and the OSPF Route Type extended communities, where candidates mistakenly think the Route Type carries the domain information, but in reality the Route Type only encodes the OSPF path type and metric, while the Domain ID identifies the originating OSPF domain.
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
✓
OSPF Domain ID
In an MPLS L3VPN where OSPF is the PE-CE protocol, the OSPF Domain ID extended community is used to signal the OSPF domain identifier between PE routers. This allows the receiving PE to determine whether the OSPF route originated from the same OSPF domain (and thus should be redistributed as an intra-area or inter-area route) or from a different domain (requiring a Type 5 LSA). The OSPF Domain ID is carried as a BGP extended community (type 0x0005 or 0x8005) and is critical for maintaining OSPF route type semantics across the MPLS backbone.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Site of Origin
Why it's wrong here
Site of Origin (SoO) is used to prevent routing loops.
- ✓
OSPF Domain ID
Why this is correct
This community specifically carries the OSPF domain ID.
- ✗
OSPF Route Type
Why it's wrong here
OSPF Route Type carries the OSPF route type (intra/inter/type1/type2), not the domain ID.
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Route Target
Why it's wrong here
Route Target is used for VPN route import/export, not OSPF domain ID.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.