Summary

In this chapter, you've seen several potential migration strategies from classical IP backbones toward MPLS-enabled backbones. These strategies should serve only as a starting point for your own migration strategy, of course, because every network has its own specific requirements. Regardless of which strategy is adopted, a number of common steps must be followed in every network migration toward an MPLS-enabled backbone.

Start with these preparatory steps:

Determine the required software and firmware versions for all network devices in your network, based on their hardware configuration.
Determine memory requirements and any other potential upgrade requirements for all network devices in your network.
Determine the impact that MPLS might have on your network management system, specifically in areas of accounting and billing. You might use NetFlow or IP accounting on the core routers, which will cease to function as soon as these routers start forwarding labeled packets.
Test the target software version on your typical hardware platforms in a controlled lab environment to ensure that the software will be stable in your target network.
Based on the upgrade requirements, you might decide to perform partial or full migration. (This decision is even more important if you have ATM switches in your network.)

Migrate your router-based network to MPLS by following these steps:

Upgrade your network devices to the target software version. Verify that your network is stable.
If you're running BGP in your network and you plan to remove BGP from your core routers after the migration to an MPLS infrastructure, design your new BGP structure and implement it in parallel with your old structure.
Migrate the router part of your network. For networks using an ATM core infrastructure, retain the traditional ATM PVC setup and run MPLS over the ATM Forum PVCs as an interim step.
Verify that your network is stable and performs label switching as planned. Verify that the core routers forward only labeled packets.
Remove BGP from the core routers if needed. Verify that the network still performs as planned.

The following additional steps must be performed if you're migrating ATM switches toward MPLS as well:

Migrate the ATM part of your network by upgrading ATM switches and establishing a parallel Cell-mode MPLS infrastructure. Verify that the Cell-mode MPLS infrastructure performs as expected.
Using IGP cost, move your traffic from ATM Forum PVCs toward a Cell-mode MPLS infrastructure. Verify that the Cell-mode MPLS works as planned.
Remove ATM Forum PVCs from your ATM network.