Introduction to MPLS Layer 3 VPN

In the previous lessons, you built a complete MPLS domain.

Now you are going to use it for its most famous job: MPLS Layer 3 VPN.
This is the service a provider sells to connect a company's remote sites.

The MPLS Domain

Here is where you left off:

Figure 1 – An MPLS domain with five routers

Everything you know about labels, the FIB and the LFIB stays true.

Three New Roles

This domain needs three new router roles: P, PE and CE.
Let's take a look!

Three router roles, three jobs.
Start in the middle.

The P Routers

P routers, short for Provider, sit at the core: P1, P2 and P3.

Figure 2 – The routers in the middle are called P routers

They know nothing about any customer.
Their only job is moving packets through the middle of the domain.

• Intermediate LSR = P Router

• Job: swap labels, forward packets

• No visibility into any customer

The PE Routers

PE routers, short for Provider Edge, sit at the boundary of the domain: PE-1 and PE-2.
The PE is the only provider router that knows customers exist.

Figure 3 – The routers on each side are called PE routers

PE routers connect to customer sites.

Time to look at the last router type.

The CE Routers

A CE router, short for Customer Edge, is a router belonging to the customer.
In this example, two customers connect.

Customer 1 uses two CE routers: CE-R1 and CE-R2.