📖 What is Underlay Network?
The physical network infrastructure (switches, routers, and cables) that provides basic IP connectivity and routes traffic between devices.
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Sensei Says:
"In a Cisco SD-Access environment, the underlay is often built using an automated IS-IS routed access design. Its main job is just to provide reachability for the overlay."
📚 Certification: Certified Network Associate (200-301)
🔑 What are the Key Concepts of Underlay Network?
- ▸ Physical infrastructure
- ▸ Provides basic IP routing/connectivity
- ▸ Foundation for the overlay network
🎯 How does Underlay Network appear on the 200-301 Exam?
Troubleshooting basic reachability issues in the underlay before verifying the overlay.
Identifying IS-IS or OSPF as common routing protocols used to build the underlay.
❓ Frequently Asked Questions
What is the main purpose of the underlay network?
To provide robust and fast IP connectivity between all devices so that the overlay network can function.
Can the underlay network understand overlay topologies?
No, the underlay only forwards encapsulated packets and is unaware of the overlay's logical topology.
Related Terms from Certified Network Associate
Single-Mode Fiber (SMF)
Access Port
Network Address Translation (NAT)
Standard ACL
Dynamic Host Configuration Protocol (DHCP)
Port Security