Default Gateway Issue in unicast environment

Hello everyone,

Currently our project is on hold due to the gateway issue on all CCTV cameras.Below is the description of the existing setup,project goal and challenges :

Design image link : Network Design

Scope of work :

• FW01 monitoring and management - Integrator-X
• Client network management - Integrator-Y
• New deployment-our company

Goal of the project :

• All CCTVs will be monitored and videos will be saved on VMS0002 server.
• All CCTVs should be accessible from Security monitoring center and new VMS0002

Existing Setup :

• All 1400 CCTV gateway is FW01 IP 10.128.1.1
• All CCTVs,Server and firewall are in same vlan 100
• Cameras are monitored from Security monitoring center.

Current Requirement :

• CCTV to VMS0002 and vice-versa reachability.

Issue :

• Cannot ping CCTV from FW02 and VMS0002.
• Cannot change the gateway on CCTVs.

• FW01 integrator will not change their IP.

  NOTE : All camera streams are unicast.

We have same deployment in 150+ sites and wherever we faced this type of issue, FW01 and Core SW IP were interchanged and static IP was configured on core switch to reach both subnet. Now we have 3 sites network designed and managed by Integrator-Y. The issue in these site is that FW01 integrator will not change their IP(no reason given).I've to come up with the solution so that all CCTVs and VMS0002 can communicate with each other.

Need all the possible solution for this case in two scenarios :

Scenario-1.Without any changes in CCTVs and FW01(We can change configuration in Core Switch and FW02 only)

Scenario-2.With changes in CCTVs and FW01