350-501 MPLS and Segment Routing Practice Question
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?
⚠ Common exam trap
It's easy for candidates to confuse SRv6 with MPLS-based Segment Routing, assuming a separate label stack is needed for function encoding, when in fact SRv6 embeds everything into the IPv6 address itself.
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 SID is divided into locator and function (and optionally arguments).
In SRv6, the SID is encoded as a 128-bit IPv6 address that is explicitly divided into three parts: the Locator (identifies the node or prefix), the Function (identifies the specific behavior or instruction), and optionally Arguments (additional parameters). This structure allows path isolation by assigning unique locator/function combinations per service, enabling per-service steering without additional label stacks.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
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