350-501 Services Practice Question
A customer requires MPLS Layer 2 VPN connectivity between two sites using Pseudowire. Which control protocol is used to signal the pseudowire label?
⚠ Common exam trap
Many candidates confuse BGP's role in MPLS Layer 3 VPNs (where it distributes VPNv4 routes and labels) with pseudowire signaling, leading them to incorrectly select BGP for Layer 2 VPN pseudowire setup.
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
✓
LDP
B is correct because LDP (Label Distribution Protocol) is the standard control protocol used to signal pseudowire labels in MPLS Layer 2 VPNs. Specifically, the Targeted LDP (T-LDP) session between the two Provider Edge (PE) routers exchanges the Virtual Circuit (VC) label, which is the inner label used to identify the pseudowire. This is defined in RFC 4447 and is the default signaling mechanism for AToM (Any Transport over MPLS).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RSVP-TE
Why it's wrong here
RSVP-TE is for MPLS-TE tunnels.
- ✓
LDP
Why this is correct
LDP signaled pseudowire is used in AToM.
- ✗
BGP
Why it's wrong here
BGP is used for pseudowire autodiscovery, not signaling.
- ✗
OSPF
Why it's wrong here
OSPF is an IGP, not used for pseudowire.
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.
Go deeper
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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.