300-510 · Question #33
Refer to the exhibit. A network operator wants to expand the segment routing global block in upcoming maintenance. The operator must ensure that the changes to the segment routing global block have no
The correct answer is C. router ospf 1 area 0 interface Loopback0 prefix-sid absolute 19002. The key distinction is between 'index' and 'absolute' SID assignment. A 'prefix-sid index' value is relative to the SRGB base label - if the SRGB base changes (as it would during an SRGB expansion), the actual MPLS label assigned to the prefix-SID also changes, causing disruption
Question
Refer to the exhibit. A network operator wants to expand the segment routing global block in upcoming maintenance. The operator must ensure that the changes to the segment routing global block have no adverse impacts on the prefix-sid associated with the loopback0 interface used within the OSPF domain. Which command can the operator use to enforce R2 to have a strict prefix-sid assignment to loopback0? A. B. C. D.
Exhibit
Options
- Arouter ospf 1 area 0 interface Loopback0 prefix-sid index 19002 explicit-null
- Brouter ospf 1 area 0 interface Loopback0 prefix-sid absolute 13002
- Crouter ospf 1 area 0 interface Loopback0 prefix-sid absolute 19002
- Drouter ospf 1 area 0 interface Loopback0 prefix-sid index 19002
How the community answered
(43 responses)- A7% (3)
- B9% (4)
- C81% (35)
- D2% (1)
Explanation
The key distinction is between 'index' and 'absolute' SID assignment. A 'prefix-sid index' value is relative to the SRGB base label - if the SRGB base changes (as it would during an SRGB expansion), the actual MPLS label assigned to the prefix-SID also changes, causing disruption. A 'prefix-sid absolute' value pins the SID to a specific, fixed label regardless of the SRGB boundaries, ensuring the SID label does not change when the SRGB is modified. Option C uses 'prefix-sid absolute 19002', which strictly assigns label 19002 to the loopback0 interface. Option B uses absolute but the wrong value (13002). Options A and D use 'index', making the SID vulnerable to SRGB changes.
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