Supported Platforms
Packet Forwarding Component
The packet forwarding component of the Junos traffic engineering architecture is MPLS, which is responsible for directing a flow of IP packets along a predetermined path across a network. This path is called a label-switched path (LSP). LSPs are simplex; that is, the traffic flows in one direction from the head-end (ingress) router or switch to a tail-end (egress) router or switch. Duplex traffic requires two LSPs: one LSP to carry traffic in each direction. An LSP is created by the concatenation of one or more label-switched hops, allowing a packet to be forwarded from one router or switch to another across the MPLS domain.
When an ingress router or switch receives an IP packet, it adds an MPLS header to the packet and forwards it to the next router or switch in the LSP. The labeled packet is forwarded along the LSP by each router or switch until it reaches the tail end of the LSP, the egress router or switch. At this point the MPLS header is removed, and the packet is forwarded based on Layer 3 information such as the IP destination address. The value of this scheme is that the physical path of the LSP is not limited to what the IGP would choose as the shortest path to reach the destination IP address.
This section discusses the following topics:
