350-501 Networking Practice Question
Which THREE of the following are characteristics of Segment Routing (SR-MPLS) compared to traditional MPLS with LDP?
⚠ Common exam trap
Cisco often tests the misconception that SR-MPLS still requires LDP or RSVP-TE for label distribution, when in fact the IGP itself carries the SID information, making those protocols unnecessary.
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
✓
The IGP (IS-IS or OSPF) is used to advertise prefix SIDs.
In Segment Routing (SR-MPLS), the IGP (IS-IS or OSPF) is extended to advertise prefix Segment Identifiers (SIDs), which are used to build MPLS labels directly from the IGP database. This eliminates the need for a separate label distribution protocol like LDP, as the IGP itself carries the label information within its link-state advertisements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It can only be used for transit, not for egress routers.
Why it's wrong here
Incorrect. Egress routers can also use SR.
- ✓
The IGP (IS-IS or OSPF) is used to advertise prefix SIDs.
Why this is correct
Correct. IGP extensions carry label information.
- ✓
It supports explicit path control via segment lists.
Why this is correct
Correct. Segment lists allow traffic engineering.
- ✗
Labels are distributed via multicast to all routers.
Why it's wrong here
Incorrect. IGP flooding is unicast or multicast depending on IGP.
- ✓
No need for LDP or RSVP-TE for label distribution.
Why this is correct
Correct. SR-MPLS replaces LDP.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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