Quick Answer
The answer is IPv6 extension header processing, as this is the most critical hardware capability for SRv6 at line rate. SRv6 encapsulates packets with an IPv6 header that includes a Segment Routing Header (SRH), which is a type of IPv6 extension header; for the forwarding plane to handle these encapsulated packets without performance loss, the hardware must natively process these extension headers in silicon rather than punting them to the CPU for software handling. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of the forwarding-plane requirements for Segment Routing over IPv6 hardware requirements, often appearing as a trap where candidates mistakenly choose TCAM size or MPLS label support. Remember: if the hardware cannot process IPv6 extension headers at wire speed, SRv6 fails at scale—think “SRH = extension header, so hardware must chew it, not punt it.”
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.
A service provider is deploying Segment Routing over IPv6 (SRv6) and needs to ensure that the forwarding plane can support SRv6 encapsulated packets. Which hardware capability is most critical for SRv6 at the line rate?
MPLS label swap capability
Why wrong: SRv6 does not use MPLS; it uses IPv6 extension headers.
VXLAN tunnel termination
Why wrong: VXLAN is an overlay technology not directly related to SRv6.
IPv6 extension header processing
SRv6 uses the SRH, an IPv6 extension header, requiring line-rate processing.
NAT64 translation support
Why wrong: NAT64 is for IPv6-IPv4 translation, not required for SRv6.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
IPv6 extension header processing
SRv6 (Segment Routing over IPv6) encapsulates packets with an IPv6 header containing a Segment Routing Header (SRH), which is a type of IPv6 extension header. For line-rate forwarding, the hardware must natively process IPv6 extension headers in the forwarding plane without punting to the CPU, as software processing would cause performance degradation. Option C is correct because this capability is the most critical for SRv6 at line rate.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
MPLS label swap capability
Why it's wrong here
SRv6 does not use MPLS; it uses IPv6 extension headers.
VXLAN tunnel termination
Why it's wrong here
VXLAN is an overlay technology not directly related to SRv6.
IPv6 extension header processing
Why this is correct
SRv6 uses the SRH, an IPv6 extension header, requiring line-rate processing.
Related concept
Read the scenario before looking for a memorised answer.
NAT64 translation support
Why it's wrong here
NAT64 is for IPv6-IPv4 translation, not required for SRv6.
Common exam traps
Cisco often tests the misconception that SRv6 is MPLS-based, leading candidates to incorrectly select MPLS label swap capability, but SRv6 is an IPv6-native technology that relies on IPv6 extension header processing.
Detailed technical explanation
Under the hood, SRv6 uses the Segment Routing Header (SRH) defined in RFC 8754, which is carried as an IPv6 extension header (type 43). Hardware must parse the SRH to extract the active segment (SID) and update the Segments Left field, then perform a lookup on the destination address (which is the next SID). In real-world deployments, many older ASICs cannot process IPv6 extension headers at line rate, forcing a fallback to software forwarding, which is why hardware support for extension header processing is a critical requirement.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: IPv6 extension header processing — SRv6 (Segment Routing over IPv6) encapsulates packets with an IPv6 header containing a Segment Routing Header (SRH), which is a type of IPv6 extension header. For line-rate forwarding, the hardware must natively process IPv6 extension headers in the forwarding plane without punting to the CPU, as software processing would cause performance degradation. Option C is correct because this capability is the most critical for SRv6 at line rate.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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