- A
P routers store all customer VPN routes in their global routing table.
Why wrong: Incorrect. P routers only carry IGP and MPLS labels; VPN routes are stored only on PE routers.
- B
CE routers perform MPLS label switching between PE routers.
Why wrong: Incorrect. MPLS label switching is done by P routers; CE routers typically do not participate in MPLS.
- C
PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.
Correct. MP-BGP is used to distribute VPNv4 routes with RD and RT.
- D
CE routers participate in the service provider's IGP to exchange loopback addresses.
Why wrong: Incorrect. CE routers are not part of the SP IGP; they exchange routes with PE via eBGP or static.
- E
PE routers maintain separate VRF tables for each customer VPN.
Correct. VRFs isolate customer routing tables on the PE.
Quick Answer
The answer is that PE routers maintain separate VRF tables for each customer VPN, while CE routers do not participate in the service provider’s IGP. This is correct because in an MPLS L3VPN architecture, the PE router isolates each customer’s routing information using Virtual Routing and Forwarding (VRF) instances, and it advertises those customer routes across the provider backbone via MP-BGP with route distinguishers and route targets. The CE router, in contrast, simply exchanges standard IP routes with its directly attached PE and has no awareness of the MPLS core or the service provider’s interior gateway protocol. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this concept tests your understanding of the fundamental separation of control and forwarding planes in MPLS L3VPN deployments. A common trap is assuming that CE routers run MP-BGP or maintain VRF tables, when in fact they only run a standard routing protocol (e.g., eBGP, OSPF, or static) with the PE. A helpful memory tip: PE = Provider Edge, which “peels” VPNs apart using VRFs; CE = Customer Edge, which stays “clueless” about the MPLS core.
350-501 Architecture Practice Question
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 designing an MPLS L3VPN network to provide Layer 3 VPN services to multiple customers. Which two statements correctly describe the roles of the Provider Edge (PE) and Customer Edge (CE) routers in this architecture?
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
PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.
PE routers maintain separate VRF tables for each customer VPN and advertise customer routes via MP-BGP with route distinguishers and route targets. CE routers do not participate in the service provider's IGP.
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.
- ✗
P routers store all customer VPN routes in their global routing table.
Why it's wrong here
Incorrect. P routers only carry IGP and MPLS labels; VPN routes are stored only on PE routers.
- ✗
CE routers perform MPLS label switching between PE routers.
Why it's wrong here
Incorrect. MPLS label switching is done by P routers; CE routers typically do not participate in MPLS.
- ✓
PE routers advertise customer routes via MP-BGP with route distinguishers and route targets.
- ✗
CE routers participate in the service provider's IGP to exchange loopback addresses.
Why it's wrong here
Incorrect. CE routers are not part of the SP IGP; they exchange routes with PE via eBGP or static.
- ✓
PE routers maintain separate VRF tables for each customer VPN.
Why this is correct
Correct. VRFs isolate customer routing tables on the PE.
Related concept
Static NAT maps one inside address to one outside address.
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.
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FAQ
Questions learners often ask
What does this 350-501 question test?
Architecture — This question tests Architecture — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: PE routers advertise customer routes via MP-BGP with route distinguishers and route targets. — PE routers maintain separate VRF tables for each customer VPN and advertise customer routes via MP-BGP with route distinguishers and route targets. CE routers do not participate in the service provider's IGP.
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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Last reviewed: Jun 24, 2026
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