The correct answer is that the SRv6 SID structure is divided into a locator and a function, with arguments being an optional part of the function. This is because an SRv6 SID is a 128-bit IPv6 address, where the locator acts as the routing prefix that identifies the SRv6-capable node or specific path, and the function defines the specific behavior or instruction to be executed on packets matching that SID. The arguments, when present, provide additional context for the function, such as service parameters or flow identifiers. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how SRv6 enables path isolation by encoding both the network location and service action within a single SID, often appearing in questions about segment list construction or traffic engineering. A common trap is confusing the locator with the entire prefix or forgetting that arguments are optional; remember that the locator is the routing part, the function is the action, and arguments are just extra details. A helpful memory tip is “Locator leads, Function follows, Arguments are optional swallows.”
350-501 MPLS and Segment Routing Practice Question
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
A service provider is implementing Segment Routing over IPv6 (SRv6) in their core. They want to provide path isolation for different services using SRv6 SIDs. Which SID structure is used to encode both the locator and the function?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SID is divided into locator and function (and optionally arguments).
An SRv6 SID is 128 bits; the locator is the prefix portion, and the function is the remaining bits. Option A is incorrect because the prefix is the locator. Option C is incorrect because the SRv6 SID includes both. Option D is incorrect because the argument is optional and part of the function.
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
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The SID is divided into locator and function (and optionally arguments).
Why this is correct
SRv6 SID is structured as Locator:Function:Args.
Related concept
Static NAT maps one inside address to one outside address.
✗
The SID uses a separate label stack for function encoding.
Why it's wrong here
SRv6 does not use labels; it uses the IPv6 header directly.
✗
The SID is an IPv6 address without any encoding.
Why it's wrong here
The IPv6 address is used, but it encodes locator and function.
✗
The SID consists of a prefix only.
Why it's wrong here
The prefix is the locator, but the full SID includes locator and function.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
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
How to think about this question
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.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
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
How this comes up in practice
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
Got this wrong? Here's your next step.
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.
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The SID is divided into locator and function (and optionally arguments). — An SRv6 SID is 128 bits; the locator is the prefix portion, and the function is the remaining bits. Option A is incorrect because the prefix is the locator. Option C is incorrect because the SRv6 SID includes both. Option D is incorrect because the argument is optional and part of the function.
What should I do if I get this 350-501 question wrong?
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.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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