Loopback addresses are very useful for troubleshooting and for device management. What is true about the loopback interfaces?

Question

Options

• ANot required for underlay connectivity using OSPF
• BShould be avoided if NSX is used as an overlay
• CNot required for EVPN VXLAN
• DThey need to be advertised for underlay connectivity when using OSPF

• A
  71% (15)
• B
  10% (2)
• C
  14% (3)
• D
  5% (1)

Explanation

Loopback interfaces are not required for OSPF to establish adjacencies and provide underlay connectivity - OSPF forms neighbor relationships and advertises routes over physical interfaces just fine without any loopback being configured. Option A is correct because OSPF underlay functionality is independent of whether loopbacks exist.

Why the distractors are wrong:

• B is wrong: Loopbacks are actually beneficial when NSX is used as an overlay - they provide stable, always-up addresses for tunnel endpoints, so they should not be avoided.
• C is wrong: Loopbacks are required for EVPN VXLAN, as they serve as the VTEP (VXLAN Tunnel Endpoint) source IP addresses that must be reachable across the fabric.
• D contradicts A directly - since loopbacks aren't required for OSPF underlay connectivity, there's no requirement to advertise them for that purpose (though in EVPN VXLAN designs, loopbacks are advertised via OSPF so VTEPs can reach each other, but that's driven by the overlay need, not the OSPF underlay itself).

Memory tip: Think "OSPF runs on roads (physical links), not houses (loopbacks)." Loopbacks become critical only when you need a stable home address for overlay tunnels like VXLAN - the underlay routing protocol doesn't care if a loopback exists.

No community discussion yet for this question.