DNS domain which resolves names to local IP addresses

Actually there is Xip.io which does exactly what you asked for: http://xip.io/

For example 192.168.1.128.xip.io resolves to 192.168.1.128.

Yes, there is a service like that: http://freedns.afraid.org/

You can login there and have free subdomains you can use for testing.

For example, right now i have "web.leet.la" pointing to "192.168.1.1".

And just for you there is "ts.leet.la" pointing to "192.168.1.128".

Feel free to do a DNS-lookup on it and use it as you need.

And if this is not what you're asking/looking for then the answer is No. An external service that literally maps 'portal-admin.localhost' or 'domain192-168-1-128' to '192.168.1.128' does not exist :-)