I have been working on a specific topology by demonstrating the ISP core backbone. I had attached the sample network topology for your reference.
How are the Internet services provided to customers where CE connects to one of ISP’s PE routers in an Internet VRF and from that PE1 to PE2
the VPWS L2 tunnel VPN is used and now PE2 directly connects to IGW (Internet Gateway) using L2 and L3 connectivity.
I am wondering why they use both L2 and L3 connectivity between PE2 and IGW. Could you please share or assist on this why they use both connection and where are the Internet gateway IP addresses are configured that are given to customers, is that IGW sets the gateway address?
Based on the diagram that you shared, it seems that the ISP backbone is being used for several purposes. Υou have Customer A who is using the network for MPLS services, while Customer B is using it to reach the IGW using VPWS, which is essentially a Layer-2 tunneling technology.
The EVPN-VPWS is a BGP control plane solution for point-to-point services. It implements the signaling and encapsulation techniques for establishing an EVPN instance between a pair of PEs. It has the ability to forward traffic from one network to another without MAC lookup. … The EVPN-VPWS technology works on IP and MPLS core; IP core to support BGP and MPLS core for switching packets between the endpoints.
So VPWS uses BGP as the control plane to create a point-to-point connection for the purposes of tunneling Layer 2 traffic.
Each connection type serves a different purpose. The Layer 2 connection i used so that Customer B can obtain a Layer 2 connection to the IGW, while the Layer 3 connection is used to serve MPLS services.
Without knowing more about the services running on the network, and the requirements of connection between the IGW and other endpoints on the ISP topology (such as Customer A and any other customers connected to PE3) we cannot know how the Layer 3 connection is being leveraged.
Keep in mind that beyond the VPWS circuit, the Layer 3 MPLS topology can be used to route traffic from other customers to the internet via the IGW. For example, Customer A may obtain access to the Internet via the IGW over an MPLS VPN, in which case the layer 3 connectivity to the IGW is necessary.
It all depends upon the services and infrastructure being used and offered on the ISP network. Does that make sense?
