Quick Answer
The correct answer is that Segment Routing eliminates per-flow state on transit routers, which is a defining characteristic of this technology. Unlike traditional MPLS or RSVP-TE, where every intermediate router must maintain forwarding state for each traffic flow, Segment Routing encodes the entire path as an ordered list of segments in the packet header itself, allowing transit routers to simply forward based on the top segment without storing any flow-specific information. This concept is frequently tested on the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, often as a distractor against options that claim Segment Routing requires a centralized controller or lacks path selection—it actually supports both distributed and centralized control planes. A common trap is confusing the lack of per-flow state with a lack of path selection, but remember that the source router explicitly chooses the path via the segment list. Memory tip: think “no state, just steer”—transit routers steer packets using the segment list, not per-flow tables.
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO are characteristics of Segment Routing?
Uses only IPv6 data plane
Why wrong: SR can use MPLS or IPv6.
Source routing capability
SR specifies path in the packet header.
Requires RSVP-like signaling for path setup
Why wrong: SR does not use explicit signaling.
No per-flow state on transit routers
Transit routers only forward based on labels.
Requires a centralized SDN controller
Why wrong: SR can operate without a central controller.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Source routing capability
Options B and C are correct. Segment Routing uses source routing and does not require per-flow state. Option A is wrong because it does have a path selection mechanism. Option D is wrong because it uses MPLS or IPv6 data plane. Option E is wrong because it works with distributed control plane.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Uses only IPv6 data plane
Why it's wrong here
SR can use MPLS or IPv6.
Source routing capability
Why this is correct
SR specifies path in the packet header.
Related concept
Static NAT maps one inside address to one outside address.
Requires RSVP-like signaling for path setup
Why it's wrong here
SR does not use explicit signaling.
No per-flow state on transit routers
Why this is correct
Transit routers only forward based on labels.
Related concept
Static NAT maps one inside address to one outside address.
Requires a centralized SDN controller
Why it's wrong here
SR can operate without a central controller.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
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FAQ
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
The correct answer is: Source routing capability — Options B and C are correct. Segment Routing uses source routing and does not require per-flow state. Option A is wrong because it does have a path selection mechanism. Option D is wrong because it uses MPLS or IPv6 data plane. Option E is wrong because it works with distributed control plane.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 350-501 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 24, 2026
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