NAT gateways are often given the first usable address in an address space.

Do any protocol specs require this? Or is this just a convention?

I skimmed RFC 1918 and RFC 2663 but didn't see anything related to this question.

Edit: Removed off-topic words.

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1 Answer 1


Gateways (routers) do not necessarily run any NAT variant (you do not NAT on routers internal to your own network; use NAT for private<->public or overlapping addressing, but NAT is not a substitute for routing). Routers are just hosts on the LAN that know how to reach other networks, so they can be assigned any valid host address on the network.

Some people always assign the first usable host address, some always assign the last usable host address, and some assign any usable host address. It does not matter which usable host address, but it is a best practice to pick something and consistently do it the same way every time you assign a router address.


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