There are two types of router in an MPLS network:

• READ: Label Edge Router or Provider Edge router (PE) – Responsible for classifying and labeling packets entering the MPLS cloud. It is also responsible for removing the label from packets before leaving the MPLS cloud. 
• LSR: Label Switch Router or Provider router (P) – Responsible for the transmission of already labeled packets.

MPLS (Multiprotocol Label Switching) is a routing technique that uses labels to make packet forwarding decisions across a network.

Its operation is fundamentally internal to a network of a service provider or a large company, facilitating efficient traffic between locations within the network.

However, when it comes to sending traffic to the Internet, which is an external network, the process involves several key stages because MPLS is not used directly on the Internet.

We will explain how this process is handled:

1. Package Arrival at Last MPLS Label

• When a packet that has been routed through MPLS reaches its last hop within the MPLS network, it encounters an LSR (Label Switch Router) that acts as an exit edge. At this point, the packet still has its last MPLS label.

2. MPLS Label Removal

• At the edge LSR, the MPLS label is removed. This process is called “pop” the tag. The router then inspects the IP header of the packet to decide the next step based on its conventional IP routing table, since the MPLS label is no longer necessary or relevant outside the MPLS network.

3. Routing to the Internet

• Once the MPLS label is removed, the packet is handled like any other IP packet based on its destination. If the destination is to the Internet, the edge router uses its IP routing table to determine the best route to the destination. This part of the process may involve routing policies, NAT (Network Address Translation) if you are leaving a private network, and any other security settings such as firewalls.

4. Transmission to Internet Provider

• The edge router will forward the packet to the appropriate next hop, which could be another router within the service provider's network or directly to an ISP that connects to the Internet. This router will handle the packet using standard IP routing without considering MPLS, since MPLS does not extend beyond the service provider's network.

5. Internet Access

• Finally, the packet is transmitted through the ISP's network to the Internet, where it will be routed to its final destination based on typical interdomain routing (e.g., BGP).

In summary, MPLS is a predominant network technology within private or provider networks to improve the efficiency of routing and traffic handling. However, when packets need to go out to the Internet, the MPLS label is removed and the packet is treated like any other IP packet, using standard IP routing to reach its final destination.