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What is L2 Reachability

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Applies to

  • ONTAP 9

Answer

L2 reachability means two devices can exchange Ethernet frames directly, on the same Layer 2 network, without a router in the path.

  • Layer 2 is the data-link layer in Ethernet networking.
  • On Ethernet that means communication by MAC address inside one broadcast domain (one VLAN, or a set of switches and bridges that extend the same VLAN).

Two hosts are L2-reachable when all of these are true:

  • They are in the same VLAN or broadcast domain.
  • Switches along the path know (or can learn) both MAC addresses and forward frames between them.
  • A frame sent to the other host’s MAC arrives at that host. Broadcasts and multicasts in that VLAN reach it as well.
  • For IP, ARP (IPv4) or Neighbor Discovery (IPv6) can resolve the other host’s MAC, which only works when they share that L2 segment.

A typical check is: from host A, can you ARP for host B and then send a frame that B receives? If yes, A has L2 reachability to B.

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