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Routing Table:

100.64.29.0/24  gw 192.0.2.196
100.64.30.0/24  gw 192.0.2.196
100.64.36.0/23  gw 192.0.2.195
100.64.40.0/24  gw 192.0.2.195
100.64.136.0/24 gw 192.0.2.195

Routing Table - They are actually real public IPv4 network. I changed to 100.64/10 network to keep it generic.

100.64.29.0/24  gw 192.0.2.196
100.64.30.0/24  gw 192.0.2.196
100.64.36.0/23  gw 192.0.2.195
100.64.40.0/24  gw 192.0.2.195
100.64.136.0/22 gw 192.0.2.195
100.64.146.0/24 gw 192.0.2.196

EDIT: Drawning and long story short.

Today:

+----------------+       +------------------+       
|                | ----> | Firewall Dept #1 | -----------\
|                |       | 192.0.2.195/26   |            |
| Switch         |       +------------------+       +---------------+
| Layer 2 (WAN)  |                                  | Internal Core |
| 192.0.2.193/26 |       +------------------+       +---------------+
|                |       | Firewall Dept #2 |            |
|                | ----> | 192.0.2.196/26   | -----------/
+----------------+       +------------------+

What we want:

+----------------+       + -----------------+
| Layer 2 (WAN)  |       | Unified Firewall |       +---------------+
| 192.0.2.193/26 | ----> | 192.0.2.195/26   | ----- | Internal Core |
|                | ----> | 192.0.2.196/26   |       +---------------+
+----------------+       +------------------+

Routing Table:

100.64.29.0/24  gw 192.0.2.196
100.64.30.0/24  gw 192.0.2.196
100.64.36.0/23  gw 192.0.2.195
100.64.40.0/24  gw 192.0.2.195
100.64.136.0/24 gw 192.0.2.195

Issues:

• I don't have management of the Layer 2 Switch.
• Our management start on the firewalls.
• I can't use one cable from the Layer 2 Switch to bind two IP's on the Firewall due to security policies on the Layer 2 Switch. So both cables must be connected with distinct networks.
• I can find use some addresses from our IPv4 pool on the Firewall, but to do this I must preroute before the firewall. I can use the "Internal Core" for this, but I don't know how.
• Separate routers solves this.
• We do have a Cisco Nexus 3048 Switch, so we can do some wizardry on this guy. That's why I mentioned VRF on the first place.

And this table cannot be unchanged since we don't have access to it.

And this table cannot be changed since we don't have access to it.