discovering a service behind a nated network

[linux user <linuxteam () gmail com>]

Hiya All,
 
I would like to discover if a service that is behind a NATed network
is still working, for
example if a web server is in a private network, Nated behind a
gateway, how could i from an external network check if the server is 
down/ or there are network problems between the server and the
gateway? is there a way to use a tool such as traceroute for
NATed/Firewalled network from an external link?

The reason i am asking this is because i have been asked that
question on a job interview, and i did  not know what the correct
answer was, it was related to a web cluster farm then.

another reason is howto troubleshoot a service that has been port forwarded from
the gateway, the port forwarding works for other services, but this
specific service is not reachable, and you can not tell whether the NATed box
was down, or the route was down, or what, you could debate that you
can use ssh to
the gateway server, but then that is run by a different dept. and you
have no access to that.

sorry if my English langauge is a bit rusty

TIA

Anst

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