Question about docker to docker communication

[Romany]

So I have a ESPhome docker installed on Unraid - IP address of 192.168.1.16.  I have a Docker of Zoneminder (ZM) installed with an address of 192.168.4.20.  I have 2 networks obviously - the 192.168.4.20 is VL400.  Both networks defined  on my PFSENSE firewall - one for the 192.168.1.0/24 network - the other for VL400 - 192.168.4.0/24.   Default GW for Unraid is 192.168.1.1.    The Unraid VL400 address is 192.168.4.30.   ESPhome needs to be able to reach ZM's address - the 192.168.4.20 - but cannot.   After lots of digging and packet capturing this is what's happening.   ESPhome will send a packet to ZM - if will stay in Unraid cloud - and the Unraid 192.168.4.30 interface will send out arps asking for the mac address of 192.168.4.20 - I see those arp requests in my packet capture on the firewall (normal ARP broadcasts) - but no response.   Unraid never gets a MAC response from the ZM docker to complete the communication.   The Unraid interface IP and the ZM DOcker IP are both in different "virtual" spaces apparently.    If I had the ZM docker on my 192.168.1 network there would not be a problem - but I want to keep all those Chinese cameras on their own isolated layer 2 network - and ZM on it also - so that video traffic stays off my firewall.    I have came up with a temporary solution involving double NATS on my firewall (probably permanent unless someone much more knowledgeable than I am on Dockers can provide a "all you need to do") solution).   This is more of an academic question than anything else - having a more elegant solution is not on my bucket list...

 

Thanks.

Romany