The network we are going to present here is actually working in real life. Of course, we will replace the real IP addresses of the routers and servers.
The network is deployed at a large provider of Internet and IP telephony services. The point is to understand how packets flow through the network, to identify the security breakpoints, and build proper firewalls for the network.
We will present here only the important parts of the network as it is.
Let's start by looking at the network architecture and explain how the network is built and what's in the network.
The core of the network is represented in the following figure:
Core-1 is a router that has one FastEthernet connection to an ISP from which we buy 34Mbps of internet services. It is located in the main datacenter of this company and has a fiber optic connection at 100Mbps to Core-2 located in another datacenter. Core-1 also has a fiber optic connection at 1000Mbps (1Gbps) to Core-3...