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Internet services B31

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MPLS Backbone Network

Overview

This example preserves the external interconnections of the mini Internet while adding core routers and enabling MPLS within transit AS2. Other autonomous systems retain their original routing behavior. By inspecting MPLS, LDP, and OSPF state on border and core routers and verifying cross-AS communication, you can understand how label distribution and backbone forwarding work together. You can further modify internal links or simulate node failures to compare forwarding paths and recovery processes. Running this example requires the corresponding Linux MPLS kernel support on the host.

Mini Internet With MPLS Transit AS

This example is based on examples/internet/B00_mini_internet. It keeps the same Internet exchanges, transit ASes, stub ASes, route-server peerings, private peerings, and customized AS154 host, but changes one large transit AS:

AS2 uses MPLS.
AS3, AS4, AS11, AS12, and all stub ASes keep the normal B00 routing behavior.

AS2 is a good demonstration target because it is a tier-1 transit AS connected to IX100, IX101, IX102, and IX105. Its IX presence and peerings are copied from B00. Its internal links are changed to pass through non-edge core routers, so the MPLS layer has an internal provider backbone to configure.

Host System Support

MPLS requires support from the Linux kernel on the emulator host. Before running the Docker runtime, load the MPLS kernel module as root:

modprobe mpls_router

Depending on the host distribution, mpls_iptunnel and mpls_gso may also be needed.

Implementation

The key difference from B00 is the Mpls layer:

mpls = Mpls()
mpls.enableOn(2)

The emulator then adds mpls along with the usual routing layers:

emu.addLayer(base)
emu.addLayer(Routing())
emu.addLayer(ebgp)
emu.addLayer(mpls)
emu.addLayer(Ibgp())
emu.addLayer(Ospf())

The MPLS layer masks AS2 from the regular Ibgp and Ospf layers and installs MPLS/LDP/OSPF configuration on AS2’s border and core routers. Other ASes continue to use the normal B00 behavior.

Standard Arguments

The example accepts both the legacy platform argument and the newer named arguments:

python examples/internet/B31_mini_internet_mpls/mini_internet_mpls.py amd
python examples/internet/B31_mini_internet_mpls/mini_internet_mpls.py --platform amd --output examples/internet/B31_mini_internet_mpls/output
python examples/internet/B31_mini_internet_mpls/mini_internet_mpls.py --dumpfile examples/internet/B31_mini_internet_mpls/base_internet_mpls.bin

Supported arguments:

  • amd|arm: optional legacy platform argument.
  • --platform amd|arm: named platform argument.
  • --output PATH: output folder for Docker compiler results.
  • --dumpfile PATH: save a serialized emulator instead of compiling Docker output.
  • --hosts-per-as N: number of hosts created in each stub AS.
  • --override / --no-override: control whether existing output is replaced.
  • --skip-render: compile without calling emu.render() first.

TestRunner Lifecycle

This example includes an example.yaml manifest for seedemu.testing. Run these commands from the repository root:

python seedemu/testing/cli.py clean examples/internet/B31_mini_internet_mpls/example.yaml
python seedemu/testing/cli.py compile examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31
python seedemu/testing/cli.py build examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31
python seedemu/testing/cli.py up examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31
python seedemu/testing/cli.py probe examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31
python seedemu/testing/cli.py test examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31
python seedemu/testing/cli.py down examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31

The full lifecycle can also be run with:

python seedemu/testing/cli.py all examples/internet/B31_mini_internet_mpls/example.yaml --artifact-dir ci-artifacts/b31

The readiness stage checks representative AS2 MPLS border/core routers, unchanged non-MPLS transit routers, and stub hosts. The probe stage checks that reachability still works across the mini Internet. The custom test_runtime.py program additionally checks that AS2 routers have MPLS/LDP configuration on the expected internal links and that an AS3 router does not have MPLS configuration.

Source: SEED Emulator · B31 README

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