What is the point of public addresses in Layer 2? Why or when do we need it? When is it healthy to use? Or is it even a common thing?

Sorry I am kinda new at networking and I just googled it but couldn't find any discussions about it.

The definition I found on Google was this one:

One-to-one (1:1) Layer 2 NAT is a service that allows the assignment of a unique public IP address to an existing private IP address (end device), so that the end device can communicate on both the private and public subnets.

  • Layer-2 NAT isn't a thing.
    – Zac67
    Dec 1, 2021 at 7:38
  • @Zac67 I was confused because Cisco had a doc about it. Thanks to Ricky clarified everything. Dec 1, 2021 at 7:39

1 Answer 1


That's not "layer-2", that's "layer-3" aka IP. You can't find anything on "layer-2 NAT" because it isn't a thing. IP addresses exist at layer-3. Nothing at layer-2 is being changed, or needs to be changed.

Cisco really should stop calling it that. A switch that understands any layer-3 protocol is no longer a layer-2 only device. NAT is occurring at layer-3, just on a device that otherwise is not a layer-3 device. (A man-in-the-middle can do anything to the traffic.)

[Note: The OP's quoted text is from Cisco documentation for the Industrial Ethernet line.]

  • That's what confused me. Cisco made this definition on their docs. It even has configuration instructors that you do by using IPs. The reason I was confused was IPs are used in Layer 3 and public addressing doesn't make much sense in Layer 2. Dec 1, 2021 at 7:32
  • 2
    I know Cisco has gone down hill over the years, but this a whole different fruit cake. It's like the marketing morons are designing things now.
    – Ricky
    Dec 1, 2021 at 7:36
  • Thanks for clarifying. I understand now and I won't take it serious. I was really confused. I verified the answer and upvoted. Dec 1, 2021 at 7:38

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