350-501 Services Practice Question
Which THREE factors must be considered when deploying MPLS Layer 3 VPN services to ensure optimal scalability and convergence?
⚠ Common exam trap
Cisco often tests the misconception that eBGP is required between PEs for VPNv4 exchange, when in fact iBGP (often with route reflectors) is the standard, and eBGP is only used at the CE-PE edge.
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
✓
Label distribution via LDP or TDP must be consistent across all P routers.
Consistent label distribution across all P (Provider) routers is essential for MPLS L3VPN scalability and convergence. LDP (Label Distribution Protocol) or TDP (Tag Distribution Protocol, Cisco proprietary predecessor) must be uniformly configured to ensure a seamless label-switched path (LSP) from ingress to egress PE. Inconsistent label distribution can cause label binding mismatches, leading to forwarding failures or suboptimal convergence during topology changes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Label distribution via LDP or TDP must be consistent across all P routers.
Why this is correct
Inconsistent label distribution can cause label mismatch and forwarding failures.
- ✓
Route reflectors should be used to reduce the number of BGP sessions in the service provider core.
Why this is correct
Route reflectors reduce BGP session mesh and improve scalability.
- ✗
All PE routers must be directly connected via eBGP to exchange VPNv4 routes.
Why it's wrong here
Route reflectors allow iBGP sessions, not direct eBGP between all PEs.
- ✓
The number of VRFs per PE router is limited by available memory and route processing capacity.
Why this is correct
Memory and CPU constraints limit the number of VRFs a PE can support.
- ✗
The use of BGP next-hop-self is mandatory to prevent routing blackholes in multi-area IGP environments.
Why it's wrong here
Next-hop-self is a design choice, not mandatory; blackholes can be avoided with proper IGP design.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.