MPLS enables service providers to create virtual private networks for customers by applying labels to packets and forwarding them through MPLS tunnels based on the label. This allows separation of customer traffic, improves routing performance, and enables both layer 2 and layer 3 services across wide areas.

1. MPLS Networks 10000ft view
This document explains the role and
benefits of MPLS in service provider
network for non technical staff.
Michael Gannon 10/04/2016

2. The Service Provider Network
• Native IPv4 core running IP routing protocol which only learns about IP addresses that
belong to the internal service provider network.
• Each router is configured with a “system” address (loopback interface). This means that the
router has a consistent address that can be used to reach the router even when the primary
network link fails.
Michael Gannon 10/04/2016

3. MPLS enabled network
• LDP - Each router sends a message to adjacent
neighbors with a label ID for any IP addresses in
its routing table.
• When the router wants to send traffic to a
remote router first it looks at the MPLS label
forward information base (LFIB) before looking
at the native IP Routing Information Base (RIB).
The router will apply an MPLS label and forward
the MPLS frame to the next router.
• When an intermediate router receives an MPLS
labelled frame it looks in its LFIB to decide how
to process the frame.
• Swap – replace the ingress label with a
new label and forward an MPLS frame to
the next router.
• Pop – remove the outer label and perform
recursive lookup in LFIB or RIB to make a
forwarding decision.
Michael Gannon 10/04/2016

4. MPLS enabled network
• The idea is to create MPLS tunnels to the “system” IP address of each router through the
network that only uses MPLS forwarding.
Michael Gannon 10/04/2016

5. BGP and MPLS forwarding
• The next step is to establish BGP peers between all of the edge routers (PE Routers).
• Now when you connect a customer to the PE router it will only be advertised by BGP and not
by the service provider Routing Protocol
• This has the effect of making the next hop the system address of the remote PE router. The
routing logic tells the router to push the traffic through the MPLS tunnels.
Michael Gannon 10/04/2016

6. Customer Networks• VPLS – Virtual Private LAN Service.
– Router interfaces are set up as Layer 2 interfaces
– The customer devices are connected to the same IP subnetwork and appear to be on the same .
– Endpoints are setup so that traffic is forwarded through the core using MPLS.
– Good replacement for leased line networks.
– Can be configured to support multiple sites connected by layer 2.
– Service provider network looks like one giant Ethernet Switch
• VPN/VPRN – Virtual Private Network or Virtual Private Routed Network
– A virtual Router is created inside the router hardware. There can be multiple virtual router instances that logically
separate customer networks and provide an added layer of security.
– Each customer site is connected using an /30 point to point network link and exchanges Routing
Protocol information with the service provider network virtul routing instance.
– Service provider network looks like one giant IP router
Michael Gannon 10/04/2016

7. Benefits of an MPLS Enabled Network
• Reduce the size of the FIB in the core network which improves
routing lookup time, reduces CPU/memory utilization.
• Logically separates your network traffic into virtual domains
to improve security.
• Allows you to implement a mix of L2 and L3 solutions across
geographically separate sites.
Michael Gannon 10/04/2016