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That is a question for simple curiosity: In my LAN i make some hosts available by NAT entry in the DSL router for access from the Internet. That all works fine.

What i can never do is using from within the local network the WAN address to connect to my host. For example for testing if the NAT table works fine.

Ex. Local network 192.168.1.0/24, a host 192.168.1.10, my WAN fixed IP address 213.102.40.55, NAT port WAN 22 translate to 192.168.1.10 port 22.

And i cannot do ssh 213.102.40.55 when i use the same NAT'ed router to the internet.

Is this due to the NAT protocoll or type of connection that i have or anything else ?

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3 Answers 3

up vote 1 down vote accepted

What you're trying to do does not make much sense. Usually you cannot nat a request coming from public address 211.123.123.123 back to the same address as if it was coming from an external host (to understand why, you should read some documentation on natting and routing protocols).

Some enterprise-class router supports the so-called "hairpin NAT" to accomplish such kind of scenarios, but this is not something that you're going to see very often in the wild.

If you want your natted services to be available on the same hostname both from the inside and outside of your lan, the smartest solution is probably to implement your own internal DNS server.

If you want to just test your NAT configuration without going out of your office you might want to make a try connecting through some public proxy (I often use Tor for this purposes). In this case, mind the security: do not provide passwords or other private data over unencrypted channels.

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+1 for the "hairpin NAT" term –  PeterMmm Aug 2 '10 at 14:02

Some SOHO NAT routers will handle WAN loop-back, namely at least some of the Linksys & Netgear stuff.

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+1 for the WAN (NAT) loop-back reference. –  PeterMmm Aug 3 '10 at 6:18

Unless you made a configuration mistake (which we can not check - you say nothing about the hardware / software you use) it should work.

Some ISP may block certain ports incoming, though, depending on your contract - to differentiate private from commercial contracts, but also to have less problems with stupid (end user) customers not securing their systems at all.

So, it is totally possibly that your ISP blocks for example SSH access (port 443?) to your IP address BEFORE your router.

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