This blog contains experience gained over the years of implementing (and de-implementing) large scale IT applications/software.

IBM WebSphere IHS Plugin Hostname Cookies Conundrum

Whilst attempting to set up IBM WebSphere with a remote IBM HTTP Server (IHS) using the WAS Plugin, I was hitting an issue whereby cookies would only be served to the client browser when accessing the IHS server using the real host name and not the DNS alias I had created.

After 2 days of trying different combinations of configuration, I finally found this article here:
The host name DNS alias I had created used underscores.
Whilst this is permitted in the system, it is not a valid host name accord to the IETF RFCs, and therefore no cookies are served/retrievable by the WebSphere application server.
In short, always use hyphens instead of underscores in your WAS or IHS DNS aliases.