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Basic Configuration of an MPLS network

The configuration of a basic MPLS network is actually very simple and only requires a few basic steps. The requirements of such a network are the following:

1. Enable CEF: CEF is essentially what allows the imposition and disposition of labels in an MPLS network. You must make sure it is enabled globally, as well as on the specific interfaces participating in the MPLS network. How to enable CEF globally and on interfaces will be shown later. When possible enable CEF in distributed mode, which is largely platform dependent. Unfortunately it does not to pertain to the platforms used in this lab.

2. Configure IGP routing protocol: Interior Gateway Protocols are routing protocols such as RIP, IGRP, EIGRP, and OSPF. In this case OSPF was used on all the routers. The configuration of this relevant to the lab will be shown later. IGP routing protocols are needed to populate the routing tables, which CEF operation takes over and label binding ensues.

3. (Optional) Define Label Distribution Protocol: LDP by default is the label distribution protocol. The only other option is TDP, which in the real world is a overwhelming minority, if used at all.

The command to manually do this is:

router(config)#mpls label protocol {ldp|tdp}

4. (Optional) Assign LDP Router ID: LDP uses the highest IP address on a loopback interface. A loopback interface is a logical interface as opposed to an actual physical interface such as interface gigabit 0/1 of a router. Loopback interfaces are often used as management IP’s for telnet sessions, monitoring, or other forms of maintenance or management. If there is no loopback interface defined, the highest IP address on the router becomes the LDP router ID.

To force an interface to be an LDP router interface simply type the command:

router(config)#mpls ldp router -id [interface type] [number] for example,

router(config)#mpls ldp router-id gigabit 0/1

The LDP router ID is important in setting up sessions between MPLS routers to exchange label information.

5. Configure MPLS or Label Forwarding on the Interface: This part of the configuration tells the specific interfaces that they are participating in MPLS or Label Forwarding. The commands to configure this will be shown later.

Configuration of the MPLS Devices

Mirrored from the previous section, configuration of the actual lab devices will be shows in order of the steps aforementioned. The same exact procedure had to be completed on all routers except for both CE’s.

1. Enable CEF Globally on the router:

8.11.PE1(config)#ip cef

1B. Enable CEF on the MPLS participating interfaces:

8.11.PE1(config-f)#ip route-cache cef

2. Configure an IGP protocol on the Router:

8.11.PE1(config)#router ospf 1
8.11.PE1(config-router)#network 10.1.4.0 255.255.255.0 area 0

* The network statements are the networks the loopback IP’s are configured for. Directly connected networks are automatically known, loopback interface network addresses are not.

3. Define Label Distribution Protocol:

8.11.PE1(config)#mpls label protocol ldp

4. Assign LDP router ID:

*Loopback IP’s are used by default, this step was not completed.*

5. Configure MPLS Label Forwarding on the interface:

8.11.PE1(config)#interface GigabitEthernet 0/0
8.11.PE1(config-if)#mpls ip
8.11.PE1(config)#interface GigabitEthernet 0/1
8.11.PE1(config-if)#mpls ip

This concludes all the necessary commands needed for basic MPLS operation.

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