What does PE-CE mean in the context of MPLS? What are CE, P, and PE devices in MPLS and MPLS VPN?
These are foundational terms and definitions in MPLS.
MPLS is one of the most commonly used encapsulation mechanisms in Service Provider networks and before studying more advanced mechanisms, this article is a must-read.
In order to understand PE-CE, we need to understand first what are PE and CE in MPLS.
Let’s take a look at the below figure.
Note: If you are looking for a much more detailed resource on this topic, please click here.
Figure -1 MPLS network PE, P, and CE routers
In Figure-1 MPLS network is shown. This can be an Enterprise or Service Provider network. MPLS is not only a service provider technology. It can provide segmentation/multi-tenancy for the enterprise environment as well.
Three different types of routers are shown. CE, PE, and P routers.
CE devices are located on the customer site. PE and P devices are located on the Service Provider site.
If it is an Enterprise network, WAN routers can be considered PE routers, and the switches can be CE devices.
PE routers don’t have to be connected to P routers. PE routers can be directly connected to each other.
CE devices don’t run MPLS. PE devices run both IP and MPLS. P devices don’t run IP but only MPLS.
You find the above sentence everywhere when you study MPLS. It actually means CE devices don’t switch the MPLS label to function.
PE devices, when a packet arrives first lookup IP destination address and then use MPLS label to function.
P devices don’t do IP lookup at all but only switch MPLS labels. Otherwise, P devices of course have IP addresses on their interfaces as well.
In MPLS, the service can be Layer 2 or Layer 3.
In Layer 3 MPLS VPN, IP routing is enabled between PE and CE devices.
These devices have their own roles. Provider Edge and Customer Edge. The provider Edge device is attached to the customer site and the MPLS network, on the other side Customer Edge device, is at the customer site and doesn’t require MPLS protocol for its function.
Routing protocols in theory can be Static Routing, RIP, EIGRP, OSPF, IS-IS, and BGP.
All of them are IETF standards. But in real life, most service providers only provide Static Routing and BGP as a routing protocol with the customer.
PE-CE interface is only IP and not MPLS. This interface is the boundary between the MPLS network and the IP network. If Enterprise purchases MPLS VPN service, this means, the customer is receiving VPN service from the MPLS backbone service provider and the customer doesn’t run MPLS with the Service Provider. MPLS is only enabled in the Service Provider network.
A specific application of PE-CE as MPLS is called CSC (Carrier Supporting Carrier). But in basic MPLS Layer 3 MPLS VPN, the PE-CE link is always IP.
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