How to : Chromecast Blue to Blue?

I have Chromecast on Blue Wifi. I want to control Chromecast with my mob device (Wifi).
This is a Blue to Blue connection.
Chromecast streams TV from Red ISP.

I found this answer, which is about Chromecast over VLANs.
I found this answer, which is about Blue to Green access. This answer also disabled mDNS without issue.

Everything worked before I installed ipFire, so I need to configure ipFire to get things working again.
Does ipFire block Blue to Blue access by default?

Only this.


Thanks for the link but I already have the Blue network setup with MAC address filtering turned off.
I can see on ipFire the Chromecast devices connected on the Blue network. They are just not communicating with the mob phone on the same network.

If there is nothing blocking Blue to Blue comms on ipFire, then I must have another issue.

Perhaps no upnp.
Try Guest mode?

I am reasonably confident the problem is with my Wifi router. It is an ancient Cisco unit that was old when I brought it.