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Arista EOS lab 13 of 20

Troubleshooting a campus pod with MLAG and OSPF

A rack that was 'finished' on Friday doesn't work on Monday: users can't reach the application server and monitoring says the MLAG pair is degraded. Find and fix five planted faults across port-channels, MLAG, OSPF and an ACL, using a bottom-up method and EOS show commands.

Run this lab

It needs Standard: its 6 nodes are set to 6 vCPU and 9,216 MB in total.

In your workspace: Shared, then Arista EOS guided labs, then 13 - Troubleshooting a campus pod with MLAG and OSPF

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 6 vCPU and 9,216 MB together. Every lab plan includes every guided lab.

Level
Advanced
Time
About 75 minutes
Nodes need
6 vCPU, 9,216 MB
Smallest plan
Standard

The scenario

On Friday a contractor built rack 1: two MLAG leaves (leaf1a, leaf1b), an access switch (acc1) dual-homed to them, and OSPF up to spine1, which hosts the application server address 10.99.99.1. On Monday morning:

  • users in VLAN 10 (h10) and VLAN 20 (h20) can ping their gateway but not the application server;
  • the monitoring system says "MLAG POD1 degraded" and "acc1: unexpected port-channel".

The design documents are correct; the switches are not. There are five faults. Find each one, fix it with the smallest change, and prove the fix.

DeviceKey design values
spine1Et1 10.1.1.0/31 → leaf1a · Et2 10.1.1.2/31 → leaf1b · Lo0 10.255.0.1 · Lo100 10.99.99.1 (app server) · OSPF area 0, p2p · ACL APP-PROTECT in on Et1/Et2: both user VLANs may reach 10.99.99.1, nothing else may
leaf1aEt1 10.1.1.1/31 · Lo0 10.255.0.11 · Vlan10 .2 / Vlan20 .2 · Vlan4094 10.255.255.1/30
leaf1bEt1 10.1.1.3/31 · Lo0 10.255.0.12 · Vlan10 .3 / Vlan20 .3 · Vlan4094 10.255.255.2/30
MLAGdomain POD1 · peer link Po10 (Et2-3) in trunk group MLAGPEER · MLAG 20 = Po20 (Et4) to acc1
acc1Po20 = Et1 + Et2 (LACP) · Et3 h10 VLAN 10 · Et4 h20 VLAN 20
Gateways (VARP)10.10.10.1 and 10.10.20.1, MAC 00:1c:73:00:00:99
Hostsh10 10.10.10.11/24 · h20 10.10.20.11/24

What you’ll practise

  • Work bottom-up: links and port-channels, then MLAG, then routing, then policy
  • Read show mlag, show mlag config-sanity and show port-channel dense to locate layer 2 faults
  • Find OSPF adjacency problems from the neighbour table and the log
  • Use ACL counters to prove which entry drops traffic
  • Document each fault as symptom, evidence, root cause and fix

The tasks

  1. Reproduce the symptoms
  2. Port-channels between acc1 and the leaves
  3. The MLAG domain
  4. OSPF adjacencies
  5. The last mile: policy

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 a campus pod with MLAG and OSPF6 nodes, 8 links. Every link is listed as text below the diagram.spine1leaf1aleaf1bacc1h10h20Ethernet3eth0Ethernet4eth0Ethernet1Ethernet1Ethernet2Ethernet1Ethernet4Ethernet1Ethernet4Ethernet2Ethernet2Ethernet2Ethernet3Ethernet3
6 nodes, with the interface names each link uses.
Every link, as text
  • spine1 Ethernet1 to leaf1a Ethernet1
  • spine1 Ethernet2 to leaf1b Ethernet1
  • leaf1a Ethernet2 to leaf1b Ethernet2
  • leaf1a Ethernet3 to leaf1b Ethernet3
  • leaf1a Ethernet4 to acc1 Ethernet1
  • leaf1b Ethernet4 to acc1 Ethernet2
  • acc1 Ethernet3 to h10 eth0
  • acc1 Ethernet4 to h20 eth0
Nodes in Troubleshooting a campus pod with MLAG and OSPF, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
spine1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
leaf1aArista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
leaf1bArista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
acc1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
h10Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB
h20Alpine 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 13 - Troubleshooting a campus pod with MLAG and OSPF 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.