isn't the parameter ForceHostP thought to determine this behaviour? Atleast it used to work like this in ACS 3.4.x. Setting ForceHostP=0 meant that the server woudn't touch the client's header.
I'm running my first productive site on OpenACS 5.0 now with an external url of http://intranet.dnsalias.com:80/ and an internal URL of http://192.168.0.1:30018/, and coming from the "outside" I get redirected to http://intranet.dnsalias.com:30018/.
Bests, Frank
mailto:frank.bergmann_at_project-open_doc_com http://www.project-open.com/
It's great that you've got your OpenACS site going. I see Arsdigita and Redhat mentioned, not OpenACS though...
/Randy