The answer is that BGP FlowSpec can be deployed with a route reflector, and it uses the IPv4 unicast or VPNv4 address family. This is correct because RFC 8955 defines FlowSpec NLRI as a separate address family that a route reflector can propagate to its clients, enabling scalable distribution of traffic filtering rules without requiring a full BGP mesh. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how service providers leverage route reflectors to offload DDoS mitigation policies—a common trap is assuming FlowSpec requires a direct IBGP session between all peers. Remember that the route reflector acts as a central hub for FlowSpec routes, just as it does for standard unicast prefixes. A useful memory tip: think of FlowSpec as “policy as a route”—the reflector reflects the policy, not just the path.
350-501 Services Practice Question
This 350-501 practice question tests your understanding of services. 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 statements about BGP FlowSpec (RFC 8955) are correct?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
FlowSpec can be deployed in BGP sessions between a route reflector and a client.
Option A is correct because BGP FlowSpec (RFC 8955) can be deployed between a route reflector and its clients. The route reflector propagates FlowSpec NLRI (Network Layer Reachability Information) to its clients, allowing the clients to install traffic filtering rules without requiring a full BGP mesh. This is a common deployment model in service provider networks to distribute flow-spec routes efficiently.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
FlowSpec can be deployed in BGP sessions between a route reflector and a client.
Why this is correct
FlowSpec routes can be propagated via BGP within the service provider network.
Related concept
Read the scenario before looking for a memorised answer.
✗
FlowSpec uses a separate BGP session from the regular IPv4 unicast session.
Why it's wrong here
FlowSpec can be carried in the same session using additional address families.
✗
FlowSpec is designed to replace ACLs on provider edge routers.
Why it's wrong here
FlowSpec provides dynamic traffic filtering but does not replace static ACLs entirely.
✗
FlowSpec requires MPLS forwarding to operate.
Why it's wrong here
FlowSpec can operate on pure IP networks.
✓
FlowSpec uses the IPv4 unicast or VPNv4 address family.
Why this is correct
FlowSpec uses SAFI 133 (IPv4) or 134 (VPNv4) under the IPv4 AFI.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that FlowSpec requires a separate BGP session or MPLS, but the trap here is that candidates confuse the address family separation (which uses the same session) with a separate session, or assume MPLS is mandatory because FlowSpec is often discussed in MPLS VPN contexts.
Detailed technical explanation
How to think about this question
Under the hood, BGP FlowSpec uses the AFI 1 (IPv4) or AFI 2 (IPv6) with SAFI 133 (Flow-spec) to encode traffic filtering rules as NLRI. The NLRI contains type-length-value (TLV) components such as destination prefix, source prefix, protocol, port, and ICMP type/code. The actions (e.g., rate-limit, redirect, discard) are encoded in extended communities. In real-world scenarios, FlowSpec is often used for DDoS mitigation, where a controller or route reflector pushes filtering rules to edge routers to drop or rate-limit attack traffic without manual ACL configuration.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Services — This question tests Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: FlowSpec can be deployed in BGP sessions between a route reflector and a client. — Option A is correct because BGP FlowSpec (RFC 8955) can be deployed between a route reflector and its clients. The route reflector propagates FlowSpec NLRI (Network Layer Reachability Information) to its clients, allowing the clients to install traffic filtering rules without requiring a full BGP mesh. This is a common deployment model in service provider networks to distribute flow-spec routes efficiently.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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