Which device in MPLS is responsible for adding or deleting labels from packets?

The device responsible for adding or deleting labels from packets in an MPLS (Multiprotocol Label Switching) network is the Label Edge Router (LER). LERs play a critical role at the edges of an MPLS network, where they handle the ingress and egress of packets.

When a packet enters the MPLS network, the LER assigns it a label based on the forwarding equivalence class (FEC) defined for that packet. This process is known as label imposition. Conversely, when a packet exits the MPLS network, the LER removes the label, a process known as label popping. This capability to manipulate labels is essential for determining the path the packets will take through the network.

In summary, the LER is uniquely responsible for both adding labels to packets as they enter the MPLS network and removing them as they leave, facilitating the efficient routing of data based on pre-defined labels rather than on the entire IP packet headers.