2.3 Describe network virtualization concepts

What this section tests

Section 2.3 is a describe topic. The exam wants recognition and packet walks, not full fabric deployment. Do not turn this into a data center EVPN or SD-Access build guide.

You must be able to do these things:

• Explain the LISP split between endpoint identity and routing location.
• Recognize the EID, RLOC, map server, map resolver, and xTR roles.
• Explain VXLAN as Layer 2 frames carried over a Layer 3 underlay.
• Distinguish VNI, VTEP, underlay, and overlay.
• Read a packet walk and name the failing layer: underlay, mapping, or edge attachment.

The two child objectives

• 2.3.a LISP: the Locator/ID Separation Protocol. A mapping system separates who an endpoint is from where it is.
• 2.3.b VXLAN: Virtual Extensible LAN. VTEPs carry tenant frames in VNIs across an IP underlay.

Control points and proof

The mental model

LISP:  host EID behind Edge-2
       -> Edge-1 asks the map resolver where the EID lives
       -> answer: RLOC of Edge-2
       -> Edge-1 encapsulates toward that RLOC

VXLAN: frame in VLAN 10
       -> leaf maps VLAN 10 to VNI 10010
       -> VXLAN header, UDP destination port 4789
       -> outer IP packet to the remote VTEP

Both topics share one rule: the underlay only routes outer packets between locators or VTEPs. Verify the underlay first.

Exam traps

• EID and RLOC are different roles. Do not treat them as synonyms.
• VNI is not the same as VLAN, even when they are mapped together.
• VXLAN does not encrypt traffic by default.
• EVPN is a control plane used with VXLAN, not a synonym for VXLAN.
• If the underlay cannot reach the remote RLOC or VTEP, the overlay fails.

Pass check

You are ready for Section 2.3 when you can do these things:

• Explain why LISP separates identity from location.
• Walk a LISP packet from source EID to destination EID.
• Walk a VXLAN frame from source host to remote host.
• Name the control point and proof command for each technology.
• Say which layer to verify first in any overlay problem.