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Arista EOS lab 20 of 20

Troubleshooting an MPLS core and L3VPN

A weekend change left the core broken. Work up the stack from IS-IS through MPLS and segment routing to BGP and the VRFs, find five planted faults, fix each with the smallest change, and prove the service end to end.

Run this lab

It needs Standard: its 8 nodes are set to 8 vCPU and 10,240 MB in total.

In your workspace: Shared, then Arista EOS guided labs, then 20 - Troubleshooting an MPLS core and L3VPN

Run it on Standard from £5 a day

The free demo can’t run it: it has 6 vCPU and 8 GB, and this lab’s nodes need 8 vCPU and 10,240 MB together. Every lab plan includes every guided lab.

Level
Advanced
Time
About 90 minutes
Nodes need
8 vCPU, 10,240 MB
Smallest plan
Standard

The scenario

Saturday night's change window went badly. Northwind pushed new configs to the whole core, and on Monday both customers are down. Here's the design as it should be:

  • IS-IS Level 2 on every core link, with hello authentication using the key Core-Hello1 (typed, as it's hidden in the running config).
  • SR-MPLS on all four routers, node SID indexes PE1 1, PE2 2, P1 11, P2 12, and TI-LFA on.
  • Working path through P1: the P2 links cost 30 at the PEs. P2 is the protected path.
  • VPNv4 iBGP between PE1 and PE2, using Loopback0, with extended communities.
  • RED uses RT 65000:10 at both PEs, BLUE uses RT 65000:20.
HostSiteAddressGateway
red1PE1 Et3, VRF RED10.10.1.10/2410.10.1.1
red2PE2 Et3, VRF RED10.10.2.10/2410.10.2.1
blue1PE1 Et4, VRF BLUE10.20.1.10/2410.20.1.1
blue2PE2 Et4, VRF BLUE10.20.2.10/2410.20.2.1
LinkAddresses
PE1 Et1 to P1 Et110.0.1.0 and 10.0.1.1 /31
PE1 Et2 to P2 Et110.0.2.0 and 10.0.2.1 /31
PE2 Et1 to P1 Et210.0.3.0 and 10.0.3.1 /31
PE2 Et2 to P2 Et210.0.4.0 and 10.0.4.1 /31
P1 Et3 to P2 Et310.0.5.0 and 10.0.5.1 /31

Loopbacks: PE1 10.255.0.1, PE2 10.255.0.2, P1 10.255.0.11, P2 10.255.0.12.

There are five faults. Work up the stack, because each layer depends on the one below: IS-IS, then MPLS, then segments, then BGP, then the VRFs. Fix each one with the smallest change.

What you’ll practise

  • Check an MPLS service layer by layer instead of guessing
  • Find an IS-IS adjacency failure from its symptoms
  • Recognise a router with MPLS routing switched off
  • Trace an invalid VPN route to a missing node SID
  • Spot VPN routes that arrive with no route target
  • Prove the repaired path with LSP traceroute

The tasks

  1. Reproduce the tickets
  2. Layer 1: the IGP
  3. Layer 2: MPLS on every router
  4. Layer 3: segments
  5. Layer 4: BGP attributes
  6. Layer 5: the VRFs
  7. Prove the design

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of Troubleshooting an MPLS core and L3VPN8 nodes, 9 links. Every link is listed as text below the diagram.PE1P1P2PE2red1blue1red2blue2Ethernet3eth0Ethernet4eth0Ethernet3eth0Ethernet4eth0Ethernet1Ethernet1Ethernet2Ethernet1Ethernet1Ethernet2Ethernet2Ethernet2Ethernet3Ethernet3
8 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • PE1 Ethernet1 to P1 Ethernet1
  • PE1 Ethernet2 to P2 Ethernet1
  • PE2 Ethernet1 to P1 Ethernet2
  • PE2 Ethernet2 to P2 Ethernet2
  • P1 Ethernet3 to P2 Ethernet3
  • PE1 Ethernet3 to red1 eth0
  • PE1 Ethernet4 to blue1 eth0
  • PE2 Ethernet3 to red2 eth0
  • PE2 Ethernet4 to blue2 eth0
Nodes in Troubleshooting an MPLS core and L3VPN, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
PE1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
P1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
P2Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
PE2Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
red1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB
blue1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB
red2Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB
blue2Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder Arista EOS guided labs.

  3. Open 20 - Troubleshooting an MPLS core and L3VPN and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of Arista Networks. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.