[TriLUG] Router question: What's the feature called, in which a router port-forwards LAN traffic as if it were WAN traffic

[Michael Marley via TriLUG]

On 10/13/18 3:21 PM, Joseph Mack NA3T via TriLUG wrote:
> On Sat, 13 Oct 2018, Michael Marley via TriLUG wrote:
>
>> That feature is called Hairpin NAT
>> (https://en.wikipedia.org/wiki/Hairpinning).  As far as which routers
>> support all those features, I would highly recommend looking at
>> OpenWRT, which runs on many routers (including yours, I think), is
>> updated much more regularly and for much longer than most vendor
>> firmwares, and supports all those features.
>
> The linux kernel doesn't care which nic the packets come in on (at
> least for the 2.4 kernels, which is the last time I looked), so a
> packet to 50.x.x.x will be port forwarded whether it comes in on the
> WAN or the LAN.
>
> Joe
>
That isn't my experience (with 2.6+).  OpenWRT has an extra option you
can select when creating a rule to enable hairpin NAT (which creates
extra firewall rules to handle it) and without that option, hairpin NAT
does not work.

Michael