Enabling MPLS On Cisco Routers

In this MPLS lesson, we will focus on basic Cisco MPLS Configuration. We will study how to enable CEF, how to enable MPLS and how to configure label protocol ldp on Cisco routers. During this survey we will check the configuretion with various basic show command that will be useful during MPLS configurations.

 

After successfully configuration of the core part, we will discuss hiding the core routes from the customer with disabling ttl propagate. For our Cisco MPLS Configuration Example, we will use the below topology:

 

Before MPLS configuration, this configuration must be fully connected and you can ping from one end through the other. You will already find the GNS3 configuration file at the end of this article;)

 

Let’s start the configuration!

 

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PE1 Router

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PE2 Router

 

 

P1 Router

 

 

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P2 Router

 

After the configuration of core routers(P1 and P2) and the customer edge routers(PE1 and PE2), it is time to verify our configuration.

 

On router P1, use “show mpls interface” to verify that the interfaces are configured to use LDP.

 

After that check the LDP neighborship with the command “show mpls ldp discovery”.

 

Lastly use the “show mpls ldp bindings” command to confirm that LDP has provided a label for subnets within the MPLS provider core.

After the verify section we will discuss an important point. This is hiding the core routers from the customer side. As you know provider’s core must be hidden from customers. Customers must not reach to the core routers. From the customer perspective, the connection from the one PE to another, must be like one connection.

 

Without any configuration, customer side can see the core routers when they start a traceroute from one PE to another PE. Like below, the traceroute command show the core routers as hops.

 

To prevent core router from customer side, we must disable ttl propagation on routers. To do this on all routers we will use, “no tag-switching ip propagate-ttl” command.

 

PE1(config)# no tag-switching ip propagate-ttl

 

PE2(config)# no tag-switching ip propagate-ttl

 

P1(config)# no tag-switching ip propagate-ttl

 

P2(config)# no tag-switching ip propagate-ttl

 

After the configuration of this, core routers won’t seen by traceroute to the customers.

 

Lastly, on PE1 router, you can use the command to see the tags on this router.

 

We have finished basic Cisco MPLS Configuration example.

 

You can download the GNS3 configuration of this lab below.

Download Enabling MPLS Lab.