[Koha] Setting up Koha instances as Z39.50 servers

[w h]

I am running Koha 3.14.01 under Oracle VM Virtual Box and Debian 7.
I have set up a couple of instances, loaded some records, and all seems to
work reasonably.

Now I would like to set up the instances as Z39.50 servers.
Looking at koha-conf.xml I uncommented three sections as I had previously
under an older version of Koha.

It remains a mystery as how ZEBRA_SRU_BIBLIOS_PORT and ZEBRA_SRU_HOST are
established.

Previous port was hard-coded as 9998.

Now how is it possible to set the port?

Currently, port 9998 is not active and working.