Example MPLS network
In this figure, the C and CE routers can be any type of router running essentially any version of IOS, except when we will note that we are using some special feature. None of the C or CE routers run MPLS. The P and PE routers all run MPLS. The only special device in this picture is the P router called Switch-P2, which is actually an ATM switch. In our example, this will be a Cisco Lightstream 1010 that uses OC3 interfaces to connect to Router-PE1 and Router-PE2. The configuration of this device will be discussed in Recipe 26.4. Although we use a Lightstream 1010 for this purpose, any Cisco ATM switch could be readily substituted. We also have the P router called Router-P1, which is a conventional IP router. You don't need ATM for MPLS, although the two protocols do work very well together.
The point of our example is to discuss the issues and features involved in running MPLS over ATM links, which is a relatively common implementation. Because there are so many different varieties of ATM switches, all of which are configured differently, we will not cover configuration of the ATM switch in any detail, and offer the Lightstream 1010 configuration only as a general guide.
