CAS-001 · Question #107
200km (123 miles) away. This connection is provided by the local cable television company. ABC would like to extend a secure VLAN to the remote office, but the cable company says this is impossible…
The correct answer is C. MPLS. The core problem is a VLAN namespace collision: the customer wants to run VLANs end-to-end, but the service provider already uses 802.1q VLAN tags internally on their own infrastructure. Using raw 802.1q (Option D) would cause tag conflicts because both the customer and the…
Question
200km (123 miles) away. This connection is provided by the local cable television company. ABC would like to extend a secure VLAN to the remote office, but the cable company says this is impossible since they already use VLANs on their internal network. Which of the following protocols should the cable company be using to allow their customers to establish VLANs to other sites?
Options
- AIS-IS
- BEIGRP
- CMPLS
- D802.1q
How the community answered
(44 responses)- A5% (2)
- B9% (4)
- C84% (37)
- D2% (1)
Explanation
The core problem is a VLAN namespace collision: the customer wants to run VLANs end-to-end, but the service provider already uses 802.1q VLAN tags internally on their own infrastructure. Using raw 802.1q (Option D) would cause tag conflicts because both the customer and the provider would be competing for the same tag space. MPLS (Multiprotocol Label Switching) solves this by providing Layer 2 VPN services - specifically VPLS (Virtual Private LAN Service) or EoMPLS - which encapsulate customer Layer 2 frames (including their VLAN tags) inside MPLS labels. This creates a logical separation between the provider's internal infrastructure and each customer's traffic, allowing customers to run any VLAN configuration they choose without interfering with the provider's network. IS-IS (Option A) and EIGRP (Option B) are Layer 3 routing protocols and have no relevance to extending Layer 2 VLANs across a WAN.
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