l2tvpp

L2TPv2 LNS data plane for VPP, so an LNS on commodity hardware forwards beyond 10G over L2TP. Control plane stays accel-ppp(-ng); this repo adds:

Dir	What
docs/	design.md (architecture, milestones), first-test.md (how to build and test), m0-notes.md (open items)
plugin/l2tvpp/	VPP plugin: L2TPv2 decap/encap, per-session interface, worker handoff
syncd/	daemon that installs accel-ppp sessions into VPP
test/	VPP make test suite for the plugin (scapy, no NIC needed)
build/	dev-build.sh (plain VPP tree, fast loop), build-vpp-debs.sh (VyOS-identical packages), build-iso.sh
xdp/	independent fallback: XDP cpumap steering for the kernel LNS path
lab/, bench/	test rig configs and results

Testing tiers

1. Unit, no hardware: make test TEST=test_l2tvpp,test_l2tvpp_syncd inside the VPP tree the build script produces (build/work/vyos-build/scripts/package-build/vpp/vpp/). Runs in CI.
2. VM lab: VyOS ISO from build/build-iso.sh in KVM (virtio NICs), BNG an L2TP LAC (e.g. BNG Blaster) as the client. Functional and churn tests.
3. Hardware: a multicore x86 box with a DPDK-capable NIC. Throughput numbers.

Getting the plugin onto a VyOS box

• Proper: build/build-vpp-debs.sh then build/build-iso.sh, install the ISO (add system image). The plugin is inside the image's own VPP packages.
• Quick: build/build-vpp-debs.sh, copy build/out/vpp-plugin-core_*.deb to the box and sudo dpkg -i it (same VPP version, so it is a drop-in), then sudo systemctl restart vpp. Lost on image upgrade, fine for development.

VPP version tracking: VyOS current builds FDio stable/2510; build/package.toml must be re-diffed against package.toml.vyos-orig whenever VyOS bumps it.

License

• Everything except xdp/ is Apache-2.0 (LICENSE), the same license as VPP and the VyOS VPP patches, so the plugin can go upstream unchanged. Source files carry SPDX-License-Identifier: Apache-2.0.
• xdp/ is GPL-2.0 (xdp/LICENSE): the BPF program uses GPL-only kernel helpers and declares "GPL" to the verifier; the loader links libbpf (LGPL-2.1 OR BSD-2-Clause).
• Contributions use the Developer Certificate of Origin (git commit -s), as required by FD.io and VyOS.