Source Packet Routing in NetworkinG (SPRING)

The IETF has two packet-based forwarding technologies: IP and MPLS.

IP previously had a source-based routing mechanism made available through an IP Option. This mechanism has, however, not been widely used and has a number of issues that make its use inadvisable, and other mechanisms (such as RFC 1940) do not appear to have been implemented at all.

The ability of a router to influence or control the forwarding path of an individual packet or all the packets of a given Forwarding Equivalence Class (FEC) is a desirable feature for a number of reasons including Label Switched Path stitching, egress protection, explicit routing, egress ASBR link selection, and backup (bypass tunnels, Remote Loop-Free Alternates) routing. This can be achieved by facilitating source-initiated selection of routes to complement the route selection provided by existing routing protocols for both inter- domain and intra-domain routes.

Historically, distribution of MPLS label binding information was done by relying on label distribution protocols such as LDP and RSVP-TE.

Several new proposals have been made to make use of the MPLS forwarding plane in novel but backward-compatible ways, and to install forwarding instructions using information distributed by the IGP running in the network, or through the management plane. It has been suggested that similar mechanisms might also be applied in IPv6.

A BoF has been proposed for Berlin to discuss the practicalities of various use cases and to establish a consensus around the problem space and desirability of developing solutions in this area with a view to determining whether the IETF should have a Working Group on this topic. This list also serves to discuss that BoF proposal.

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