When a print request (or other IPP request) comes in to the domain, in
which the IPP Printer is located, it goes through the following steps:
1) The firewall inspects the request on the TCP layer and typically
checks the host address and the port number. If it finds that this
matches, it redirects the request to a particular proxy server. This is
standard firewall software. The proxy server may be dedicated to handle
only HTTP/IPP, or could handle several application level protocols.
2) The proxy server includes an IPP specific application process, which
would check that the request is a valid IPP request, e.g. that it is an
HTTP POST and that it contains the MIME type "application/ipp". This
software will need to be tailored and written to handle IPP.
3) If TLS is used, the proxy server can also perform the authentication
and decryption services.
4) The proxy server then redirects the request to the IPP server inside
the domain. Note that the previous steps are performed before the request
is accepted into the domain.
There are various configuration alternatives, e.g. the firewall and proxy
server may be integrated in the same box.
A couple of other observations and bits of advice:
- If you want unlimited access to an IPP printer, simply put it outside
the firewall, or on the domain border, so it can be accessed from both
outside and inside the domain.
- If you want to let requests come in through your firewall at all, you
will probably *always* use TLS for requests from outside the domain. If
you let the proxy server handle authentication and encryption, there is
no real need to use TLS between the proxy server and the IPP server. This
means that clients from inside the domain do not need to use TLS, when
accessing the IPP server.
Principal Engineer - Advanced Printing Standards - Xerox Corporation
701 S. Aviation Blvd., El Segundo, CA, M/S: ESAE-231
Phone +1-310-333 8273, Fax +1-310-333 5514