MPLS (Multiprotocol Label Switching) Transport

 

MPLS is a service provider technology where they can squeeze MPLS labels just right before the layer 2 header, so SP can route almost any type of traffic from a specific source to a specific destination using labels. There is two main benefits MPLS provides:

1 –> Improve Routing Speed

2 –> Customer Segmentation  ( Represents different customers using different MPLS labels)

 

Note: Instead of having routers forwarding packets based on IPv4 addresses, they will forward packets based on  their labels in those packets.

 

The purpose of this micro lab is to show how to enable a simple a MPLS configuration on routers and how the packets are route through the MPLS backbone.

 

Below is a diagram I will use to represents MPLS micro lab: “Another way to route packets”

 

Keep in in mind:

-> A single router is going to generate a local single label for every neighbor they have in the IP routing  table

-> A single router will advertise its local label to reach a specific destination to their neighbors.

-> A packet sent using MPLS as transport never looks at layer 3 information. (Less burden for routers)

 

 

Background

 

 

Now let’s look how MPLS will forward packets from “PE-1 to PE-5”

 

-We need to enable “MPLS IP Switching” on each router, ” Using a command –> “mpls ip” on global configuration.

-We need to enable “MPLS IP Switching” on each interface that we want to use for MPLS on each router. (mpls ip)

 

Example – 1

 

PE-1 to P-2

-PE-1 will send a packet to P-2 with a destination to (5.5.5.5 to PE-5)

-P-2 receives the request and looks for a specific label associate with route (5.5.5.5) that P-2 has in its routing table

-PE-1 and P-3 will know what “P-2” labels are for that particular route (5.5.5.5)

-P-2 has a MPLS forwarding table where it is going to swap out P-2 label and impose a new label that P-3 has created and it is associated to a route (5.5.5.5)

 

PE-1 to P-2 perspective (Packet Capture)

 

 

Example – 2

 

P-2  to P-3

->De-encapsulate its layer 2 (sees its own layer 2 MAC-addresses)

-> Processes the frame

->Looks at the Multiprotocol Label Switching Header (Layer 2.5) and check the specific label

-> P-3 is going to have forwarding information based on LDP(Label Distribution Protocol)

->  So P-3 will remove old label and impose the new label and forward the packet to P-4

 

P-3 to P-4 Perspective (Packet Capture)

 

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