Scaling Layer 3 Virtual Networks in a Campus Network

300-420 By islever Editorial Last updated

Design campus Layer 2 infrastructures Design multicampus Layer 3 infrastructures

Short answer

B A multihop MPLS core scales to hundreds of Layer 3 virtual networks with per-VRF routing tables while keeping per-VN changes at the edge only

Question

An engineer must propose a solution for a campus network that includes the capability to create multiple Layer 3 virtual networks. Each network must have its own
addressing structure and routing table for data forwarding. The solution must be scalable to support hundreds of virtual networks and allow simple configuration
and management with minimal administrative overhead. Which solution does the engineer recommend?
  1. hop-by-hop EVN
  2. multihop MPLS core Correct Answer
  3. multihop IPsec tunneling
  4. hop-by-hop VRF-Lite

Key Takeaways

The test is recognizing that the "hundreds" scalability qualifier disqualifies EVN's 32-VN ceiling and VRF-Lite's hop-by-hop overhead, leaving MPLS as the only option that meets both scale and low per-VN effort.

This 300-420 design question asks which technology scales to hundreds of Layer 3 virtual networks with minimal per-VN administrative overhead. The correct choice is a multihop MPLS core (B), since EVN caps at 32 VNs and VRF-Lite multiplies hop-by-hop configuration.

Common mistake: Choosing A (hop-by-hop EVN) because it automates VRF tagging and seems simplest, but EVN supports only 32 virtual networks per IP infrastructure and therefore fails the explicit "hundreds" requirement.

Expert Analysis

Reading the qualifiers

The question stacks four constraints that must all hold simultaneously: multiple Layer 3 virtual networks, each with its own addressing structure and routing table, scalability to hundreds of virtual networks, and simple configuration with minimal administrative overhead. The word "hundreds" is the hardest filter, and "minimal administrative overhead" is the second.

Eliminating option A (hop-by-hop EVN)

Cisco EVN automates per-VN tagging on trunk links, which does reduce hop-by-hop configuration effort compared with classic VRF-Lite. However, EVN is documented with a hard ceiling of 32 virtual networks per IP infrastructure. That ceiling sits far below the "hundreds" requirement stated in the question, so A is eliminated by the scalability qualifier regardless of how easy it is to configure.

Eliminating option D (hop-by-hop VRF-Lite)

VRF-Lite gives each VN its own VRF and routing table, satisfying the first two requirements. But "hop-by-hop" means every interface or subinterface on every hop must be manually bound to a VN. The comments note that VRF-Lite "is recommended for smaller amounts of VN requirements" and that as tenant count rises, configuring subinterfaces per VN creates "a high degree of operational complexity." Hundreds of VNs multiplied across hops violates the "minimal administrative overhead" qualifier, so D is out.

Eliminating option C (multihop IPsec tunneling)

Full-mesh IPsec tunneling for hundreds of VNs would require per-VN tunnel definitions at every site, which is the opposite of "minimal administrative overhead." C is eliminated on the simplicity qualifier.

Why B is correct

Only B, multihop MPLS core, survives the "hundreds" filter. An MPLS L3VPN core scales to hundreds or thousands of VRFs, and crucially the core routers forward on labels rather than per-VN routes, so adding a new VN touches only the edge routers—no core changes. That is what delivers the "minimal administrative overhead" at scale the question demands. Comments arguing that MPLS needs LDP, RSVP and internal BGP acknowledge upfront build cost, but that cost is paid once; per-VN operational effort stays low, which is the qualifier the question actually measures.

Official Reference

https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/Network_Virtualization/sccsolover.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When a question lists multiple hard qualifiers (hundreds, minimal overhead, own routing table), rank them and apply the most quantifiable one first—it usually eliminates half the options. Here "hundreds" kills EVN (32-VN cap) and hop-by-hop VRF-Lite immediately, so you never need to debate configuration effort for those. For technology-vs-technology choices, remember that an MPLS core adds only a one-time build cost while keeping per-VN changes at the edge, which is exactly what "minimal administrative overhead at scale" means in Cisco design doctrine.

Frequently Asked Questions

Why is hop-by-hop EVN ruled out if it simplifies VRF configuration?

EVN automates VN tagging on trunks but supports a maximum of 32 virtual networks per IP infrastructure, so it cannot satisfy the question's explicit requirement to scale to hundreds of virtual networks.

Does VRF-Lite not meet the requirement for separate routing tables per network?

VRF-Lite does create per-VRF routing tables, but because it must be configured hop-by-hop on every interface, hundreds of VNs create excessive administrative overhead, failing the simplicity qualifier.

Why is multihop MPLS considered low-overhead for hundreds of VNs?

In an MPLS L3VPN core, core routers forward by label instead of per-VN routes, so adding a virtual network only requires edge configuration—no core changes—keeping per-VN effort minimal even at scale.

More 300-420 FAQ →

Community Votes

B
40%
A
30%
D
30%

40% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 15 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 15

  1. Clauster 👍 5
    I found the Cisco White Papers that talks about EVNs - You are correct when you say we can only use 32VNs, but this is only limited to one IP Infrastructure. Since each Branch will have it's own IP Infrastructure then we can do 32VNs at each branch, so if you have 10 branches x 32VNs that puts you well over hundreds of VNs that can be supported with this feature. - MPLS Core requires tons of Administrative Overhead. - VRF Lite supports up to 8 VNs. - Only Clear answer here is A, keep in mind they also mention Easy to configure, EVN is known for easy configuration.
  2. Gilgamesh_SHA 👍 4 Answered A
    MPLS Core is overkill for a campus network, and it can't separate address structures and routing tables by itself. MPLS VPN must be deployed for this purpose. EVN supports 32 VNs per IP infrastructure/interface. I go for A due to ease of management, scalability, and operational efficiency.
  3. andrewChan 👍 4 Answered D
    Table 1 Network Virtualization Technique Comparison Chart has the answer https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/Network_Virtualization/sccsolover.html
  4. ImAlwaysRight 👍 3
    They say EVN scales up to 32 VN's maximum... But I read also that EVN is more scalable than VRF-Lite, so I am prone to agree on EVN to be the answer, but still not sure as the question mentions hundreds. Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/evn/configuration/xe-3s/evn-xe-3s-book/evn-overview.html
  5. CKL_SG 👍 3 Answered B
    VRF-lite support less than 8 vn EVN only support up to 32 vn MPLS Core support hundreds or thousand VN https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/Network_Virtualization/sccsolover.html#wp416666
Show 10 more comments
  1. Adaletherkesicin 👍 3 Answered A
    A is correct answer
  2. Hope66 👍 2
    I think A: Hop-by-hop easy virtual network (EVN) based: Hop-by-hop VRF-lite is manageable for networks with fewer numbers of virtual networks and fewer numbers of hops in a virtual network path. However, when the number of logical networks (virtual/tenants) increases, there will be a high degree of operational complexity to create and configure the interface or subinterface per VN. EVN provides the same benefits for guaranteeing traffic separation with more simplified operations. In other words, EVN builds on VRF-Lite concepts and capabilities and provides additional benefits, including the following: ■ EVN offers better end-to-end VN scalability compared to the classic hop-by-hop 802.1Q-based solution. ■ EVN offers simplified configuration and management. ■ EVN offers the capability to provision shared services among different logical groups.
  3. PicoOstrava 👍 2 Answered B
    MPLS Core (B): MPLS is designed to scale and can handle the segmentation of hundreds of virtual networks much more effectively than VRF-Lite. MPLS allows for easier management of large-scale environments, especially when multiple virtual networks need to be created and routed independently. MPLS provides both scalability and flexibility, making it a good fit for large deployments with multiple virtual networks. • VRF-Lite (D): While VRF-Lite can work in smaller networks, it doesn’t scale well for hundreds of virtual networks. It can cause administrative overhead and performance degradation as the number of VRFs increases. It is more suited for smaller to medium-sized environments rather than large-scale deployments.
  4. Clauster 👍 2 Answered B
    EVN: Supports up to 32 VN not hundreds like our requirements XX VRF Lite: Is recommended for smaller amounts of VN requirements XX IPsec Tunneling: Would be great but it requires Tons of Administrative Overhead because we would have to sit there and configure all of the VNs. Multi Hop MPLS is the best answer, you can scale MPLS for hundreds if not thousands of Virtual Networks with very little overhead because your ISP does all the work. The requirements never stated we needed to save Money which we are kinda defaulted to in our IT Heads. Answer is C
  5. python_tamer 👍 2 Answered D
    This question is super tricky. It cannot be A (EVN) because of the max 32 VN limit. That leaves us with MPLS, IPsec tunnels or VRF-Lite. MPLS is a maybe but not easy to configure. IPsec tunnels is a no. VRF-Lite is a maybe. Easier than MPLS but still plenty of admin overhead. So I think the best option is VRF-Lite: D
  6. cryptonite 👍 2 Answered B
    I disagree on EVN because it has a limitation of 32 VNs. The questions says can scale to hundreds of Virtual Network
  7. G_Singh12 👍 1 Answered A
    B is incorrect. While a multi-protocol label switching network scales cleanly to handle hundreds of virtual routing instances (L3VPNs), deploying a full internal MPLS core introduces extreme operational complexity (requiring LDP, RSVP-TE, internal BGP routing architectures, and deep engineering knowledge). This directly contradicts the requirement for a simple configuration and management architecture with minimal administrative overhead. • Cisco Easy Virtual Network (EVN) directly optimizes and automates standard VRF-Lite deployment. Instead of manually carving out hundreds of subinterfaces, EVN introduces the concept of a VNET Trunk. By issuing a single command on an interface linking two switches, the system automatically carries traffic for all specified Virtual Networks across the physical link while maintaining complete separation of addressing and routing databases—radially cutting configuration overhead and complexity.
  8. SpicyMochi 👍 1 Answered D
    D. hop-by-hop VRF-Lite To meet the requirement of creating multiple Layer 3 virtual networks, each with its own addressing structure and routing table for data forwarding, the recommended solution is hop-by-hop VRF-Lite. This solution provides logical separation of multiple routing domains over a single physical infrastructure, allowing for the creation of multiple virtual networks with unique routing tables and addressing structures. VRF-Lite is scalable, providing support for hundreds of virtual networks, and has simple configuration and management with minimal administrative overhead.
  9. mgiuseppe86 👍 1
    As right as this may be, knowing Cisco, the question is really asking what routing protocol supports the most VNs. gun to my head i will say B, but A is probably more right given the scenario.
  10. Clauster 👍 1
    https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/evn/configuration/xe-3s/evn-xe-3s-book/evn-overview.html#GUID-3E71EB2C-7ACC-47AE-9173-FB31BA61C319

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