mjhjmtu

If your connection is NAT'ed, is it possible to see your external IP address without making an outbound web request?

Any OS (Windows, Linux, etc.) is fine.

If your computer is behind NAT, it is possible for you to see the external IP address
of your router, but you need administrative access to the router.

The router knows your external IP address, so by accessing its configuration
page you can find that IP address.

Any other way will require making an external Web request.

There are a few ways that work with some NATs but nothing that's guaranteed to work everywhere.

I believe uPnP, NAT-PMP, and PCP (Universal Plug And Play, NAT Port Mapping Protocol, and the Port Control Protocol) all have ways to ask a compliant NAT gateway what the public address is, but not all NATs support these protocols. Support is more common in home gateway routers than in corporate or carrier-grade NAT solutions.

When you find yourself behind a NAT, the only sure way to see what public IP address it is translating your traffic into is to send some outgoing traffic to some public host that will report back, in a way the NAT won't translate, what address your traffic appeared to come from. Using a web based service is one way, but you could also do it by, say, SSHing into a cloud server instance and seeing where sshd says your SSH session is coming from.

I would like to add one point to already existing answers.

It also depends on the network complexity. It is possible that your computer is located within a network that has multiple external IP addresses and the router somewhere up the line sends the traffic out to the Internet based on some criteria: for example, destination IP-address, or time of day (may be one uplink channel is cheaper at night or for other reasons).

So, to be complete, a notion of "external IP address" may require defining a destination point to which your address is being external.

In the example below Router #2 could perform NAT and send traffic to either uplinks and the receiving host could see different external IP-address for the Host.

Or it could be that a certain destination (for example host1.example.com) always routes thru the Uplink A, and the host host2.example.com always routes via Uplink B. So, your external IP addresses as seen by those hosts will be different, providing that Uplink A and Uplink B are different ISPs.

 Uplink A Uplink B
------------- -------------
 | |
 | |
 | 192.168.1.1 192.168.50.50 |
 | ----------- |
 |---------------|Router #2|---------------|
 -----------
 | 192.168.100.1
 |
 | 192.168.100.2
 -----------
 |Router #1|
 -----------
 | 192.168.200.1
 |
 | 192.168.200.2
 -----------
 | Host |
 -----------

So, sending traffic out will allow to get more reliable results.

You can use a DNS request, which I believe would not fall under the category of "web request":

nslookup myip.opendns.com resolver1.opendns.com