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Re: Determine My IP Address


And the answer is....

DON'T tell the other client. Let the other client get the info for
themselves from their own network stack.

Sending your own IP address over the network as part of your payload
is ALWAYS WRONG.


On Apr 23, 2006, at 11:43 PM, Quinn wrote:

[1] Well, there are always circumstances where things like this fail. If there's a NAT between you and the remote host, for example. Or if the firewall is blocking incoming connections to your server port. Still, it's a good place to start.

I agree with Peter, it's best not to include an IP address or ports in your payload. Some protocol's require it, and some NAT implementations fix them up. FTP and RTSP come to mind.

While this isn't necessarily reliable, you can look at your IP address to see if it's in a "local" range to help you determine if you are on a NAT system. (192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8, and a few others http://www.rfc-editor.org/rfc/rfc1918.txt ) Some well meaning sysAdmin's just make this stuff up, so this technique won't always work. If it's in one of these ranges, you are probably NAT'd, if the other's IP address is in the same range, you can just report your "private" address, if it's not, you can do a trace route (RFC1393) and look for a router that's got a public IP address. That might be you (alas no guarantee). There are some services that will report to you your "real" IP address, you might try to google for it, I can't recall what it's called. (It's been a while since I thought about these kinds of issues). An important point, is that when you are behind a NAT'ed environment, your port may change as well, it's hard to tell. Also, a SysAdmin (person who setup the Router) may have setup a port map. I would suggest that you allow your users someway to specify (if you can't figure it out) what "real" IP address they have. (allow a port # as well)

-
Les Vogel
P.O. Box 598 AIM: lesv3 Jabber: email@hidden
Kihei, HI 96753-0598 Skype: lvogel3 blog: http://www.angeltech.com/ blog.html
email@hidden

(808) 870-0418


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References: 
 >How to get client IP address assigned by Cisco VPN client (From: Martin Bestmann <email@hidden>)
 >Re: How to get client IP address assigned by Cisco VPN client (From: Josh Graessley <email@hidden>)
 >Re: How to get client IP address assigned by Cisco VPN client (From: "Duane Murphy" <email@hidden>)
 >Re: How to get client IP address assigned by Cisco VPN client (From: "Justin C. Walker" <email@hidden>)
 >Determine My IP Address (was Re: How to get client IP address assigned by Cisco VPN client) (From: "Duane Murphy" <email@hidden>)
 >Re: Determine My IP Address (From: Peter Bierman <email@hidden>)
 >Re: Determine My IP Address (From: "Duane Murphy" <email@hidden>)
 >Re: Determine My IP Address (From: Quinn <email@hidden>)



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