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If I connect to my server over VNC with my external IP Address (I have port forwarding set up), it seems just as fast as if I had connected to it with the internal IP Address. This also true with other protocols, but I'm using VNC as an example.

Why is this? Does the router know its own IP Address and just redirect it to internal IP Address?

NOTE: Connecting to my server over VNC from elsewhere is noticeably slower--so its not like my upload speed is really good.

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Why is this? Does the router know its own IP Address and just redirect it to internal IP Address?

I think so

Many routers don't do that and so for example, in that situation you have to use the internal ip, when you are inside your LAN, or it won't work at all.

open a cmd window and do

C:\>tracert [your ext ip]

you'll see the route, you could paste it in. You might find it's all LAN.

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maybe disabling "nat redirection filtering" allows it, or something. It seems to be related to that setting. that may be the name. or disabling that may be the feature. – barlop Mar 10 '13 at 1:17
may be called "NAT reflection" – barlop Mar 10 '13 at 1:21
The result of the command: Tracing route to [] over a maximum of 30 hops: 1 2 ms 1 ms 1 ms [ 3] – agz Mar 10 '13 at 2:03
@agovizer ok it's just showing your external IP but other than that, it's not even leaving your LAN, so this proves your hypothesis. And by the way, your router , and any router even one that doesn't do this feature(and only sees the internal ip from the lan), any router, has two IP addresses, one is internal one(LAN side) one is external(WAN side). (really serious routers have more IPs and connect many networks not just a LAN and a WAN). – barlop Mar 10 '13 at 10:57
ok cool, but whats the difference between and both send me back to my server – agz Mar 10 '13 at 17:43

It makes sense actually.

The big things which will slow down VNC (and TCP communications in general) are 1) Size of the pipe between the 2 connections. 2) Latency 3) Packet loss.

In the case of "redirecting" through the external IP via a routing, assuming you have a half-decent router - which you obviously do - the latency increase would not really be noticeable (often < 1ms), the size of the pipe still huge, and no packet loss - so things will go very fast.

Doing address translation is not a very CPU intensive task either.

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