Let’s take a look at some of the things that we can do with MPLS. As we know, one of those things is Layer-3 MPLS VPNs, a peer-to-peer VPN scheme in which the PE and CE devices are both routers. In this scheme, a PE has a VRF for each customer to which it is […]

Having discussed Layer-3 MPLS VPNs, let’s look at some of the behind-the-scenes protocols that make things work. First, we’ll need to make the routes at the customer sites known to the PE devices. Since the CEs and PEs are routers, we can accomplish this any of these three methods: Static/default routing An IGP BGP It’s […]

Welcome back! Previously, we decided that in order for a Layer-3 MPLS VPN to function correctly, the ingress PE is going to need to push two labels onto each data packet. Let’s say that we have a data packet going from site A2 to site A3, using the topology shown in Figure 1: When the […]

Having looked at the “big picture” when it comes to MPLS, we now need to focus our attention on what happens when a data packet traverses an MPLS cloud. As you can see, this time we have three customers, A, B and C. Customers A and B each have three sites, and Customer C has two […]

When we left off last time, we were about to examine how MPLS might solve the three major problems that must be overcome in order to use routers within a WAN provider’s cloud. Those three problems are: Multiple routing tables in RAM Excessive latency Address-space collisions Refer to Figure 1 for an example topology. Note that […]

We’ve already discussed how the P (Provider) routers swap or exchange labels at each hop within the WAN cloud. The sequence of routers and labels used for a particular path is referred to as the LSP (Label-Switched Path). In general, the LSP going between the sites in the reverse direction does not use the same […]

We have three major issues that we need to deal with in order to successfully use routers within a WAN provider’s cloud: Multiple routing tables in RAM Excessive latency Address-space collisions Let’s assume that we have a WAN provider with two customers, “A” and “B”, each with three sites, as shown: Now, let’s say that an IPv4 […]

When we last left off, we were considering the feasibility of replacing a WAN provider’s P and PE devices with routers. Let’s take a look at this in greater detail, to see where any potential problems might arise. Refer to Figure 1, where we have two customers, “A” and “B”, each with three sites, connected […]

Despite the popularity and widespread use of overlay VPNs for WAN service, they do have several disadvantages. Take a look at Figure 1, in which we have the logical topology for one customer with six sites, connected using a full-mesh of PVCs: Connecting six sites in a full-mesh requires fifteen PVCs. Now consider the fact […]

When we left off, we were looking at Frame Relay as an example of a Layer-2 infrastructure. Some customers will have very few sites, and others may have thousands. The logical topology (hub-and-spoke, partial-mesh or full-mesh) for a particular customer would be negotiated between that customer and the provider, based on the customer’s number of […]