Label Switched Path

The Internet is based on the Internet Protocol IP, so it is a packet switched network. This means that data packets are routed individually through the network and it can happen that the belonging to a connection packets take different paths. That makes the behavior of the network less predictable than the behavior of a circuit-switched network such as the telephone network. The protocol allows MPLS to set up on a packet-switched network virtual circuits. In MPLS Label Switched Path hot such lines ( LSP).

An LSP is therefore a switched using MPLS path through a routed IP network. The path terminating routers are called Label Edge Router ( LER ), of which the initial node of an LSP is referred to as ingress router, the endpoint as the egress router. Typically these start and end nodes are located at the input and output points of the autonomous system (AS ) (AS Boundary Router). While the label edge routers add MPLS labels to the data packets or remove the MPLS routers exchange inside the LSP of the MPLS label and are therefore called Label Switched Router ( LSR).

The switching of the LSPs can be done completely manually, semi-automatically or fully automatically.

  • The manual version requires the configuration of each router to a LSP passes, but is ineffective in autonomous systems in the order of several dozen routers.
  • The semi-automatic version only requires the manual configuration of parts of the LSPs, so for example the way over the first three routers. The rest of the pathfinding for the LSP is left to the IGP.
  • The fully automatic version relies in determining the path for an LSP completely on a signaling protocol such as the Label Distribution Protocol (LDP ), Resource Reservation Protocol (RSVP), RSVP -TE, Border Gateway Protocol ( BGP) or CR -LDP.

Since the forwarding of data packets over LSPs for the higher transport layer is opaque, an LSP is also referred to as a MPLS tunnel.

For error detection, LSP knows different functions:

  • An LSP ping verifies that packets of a Forwarding Equivalence Class ( FEC) their MPLS path end on an LSR that serves this FEC as egress router. As a model for this function is the well-known ICMP Echo Request / Reply
  • When an LSP Traceroute for control plane of each of the LSRs LSPs an LSP traceroute packet to. In this case, it is examined whether LSRs are actually transit LSRs for the path under test. About additional information that represent the LSRs available, it can be established, for example, whether the forwarding equivalent to that established by the routing protocols path.
494204
de