How to know number of subnets on large Campus network across city (N+)

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I have an application that a vendor provides that uses Multi-cast or IGMP that that allows applications to send messages on a broadcast group. When other applications listen to this group, they can also see messages from other terminals. I don’t know if Multi-cast or IGMP is enabled and don’t want it enabled. I want to use vendor’s Multi-cast application. If any of your computers are running in separate subnets, the issue is that most network routers/switches do NOT forward multicast traffic to other subnets.
How do I explain we are on the same or different subnet on a large multi-campus network across a city? How do I know how many subnets and how many of these vendor’s multi-cast applications I’ll need to install. I need on each side of the subnet.
Vendor’s Multi-cast application is a very lightweight application that run as a service. I’ll need to install it on a server preferably, or a computer that does NOT run a vendors main product on each side of the subnet. There will be a hosting computer – normally the SQL server. The application gets installed and configured. For each of the subnets that require multicast, I will install the vendor’s Multi-cast application on a computer in that subnet.

Hi Travis. If you are authorized to do so - you would typically run a network mapping software application across your network in order to create visual documentation of your subnet design.

You can create this documentation manually of course, but this takes much more time and involves you visiting many systems in order to examine IP configurations and do ping and traceroute testing.

It seems like you might have several questions for us regarding this, and I hope I answered at least one of those. Please let me know of any follow up questions you might have. While we are not permitted to provide support for your design or your application, we always try and help where we can!