Scale improvements for LDP over RSVP / BGP-LU services

This feature enhances MPLS functionality to create chain next hops for various MPLS services, by building a translation layer between the routing information base (RIB) and forwarding information base (FIB), in order to segment multiprotocol transport tunnels.

Note that:

• Only LDP, RSVP, LDP-over-RSVP, LDP-over-RSVP-over-bypass ingress tunnels are considered for segmentation.
• Segmentation does not happen if there is only one label in the stack.
• Segmentation happens at the application boundary. A next hop with two LDP labels in its stack or two RSVP labels will not be split into two next hops with one label each.

Any route resolution over LDP or LDP-over-RSVP is changed from INH->FNH to CNH->INH->CNH->FNH in the kernel and Packet Forwarding Engine and for LDP routes in INET.3. Here, indirect next hop (INH) is an application installed in a direction toward the final next hop (FNH). Any segmented stack introduces the composite chain next hop (CNH), where the segmented portion of the label stack precedes an INH or an FNH. The chain is collapsed, and the resulting label stack is encoded in the packet header by the hardware before forwarding the packet.

By chaining labels instead of stacking them, you can make memory available for FNH label operations. You can also make memory available for CNH operations by grouping CNHs within the same unilist next hop (for ECMP) based on the label space identifier.