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CCNP Service Provider lab 11 of 23

TI-LFA: link and node protection

Protect a five-router ring with TI-LFA. Work out P-space and Q-space, read the repair path and its label stack, fail a link, and add node protection.

Run this lab

It needs Standard: its 5 nodes are set to 5 vCPU and 12,800 MB in total.

In your workspace: Shared, then CCNP Service Provider guided labs, then 11 - TI-LFA - link and node protection

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 5 vCPU and 12,800 MB together. Every lab plan includes every guided lab.

Level
Advanced
Time
About 60 minutes
Nodes need
5 vCPU, 12,800 MB
Smallest plan
Standard

The scenario

A Fellgate customer runs voice traffic that can't stand more than 50 ms of loss. An IGP on its own takes longer than that to reconverge on a big network, because every router has to learn of the failure and run SPF.

TI-LFA (Topology Independent Loop-Free Alternate) gives each router a repair path, computed before anything fails and ready in the forwarding table. The core is a ring of five routers, already running IS-IS with SR. All links have a metric of 10, except R4 to R5, which is 100. That one high metric matters, as you'll see.

DeviceInterfaceAddressConnects to
R1Loopback010.255.0.1/32
R1Gi0/0/0/010.0.12.1/30R2 Gi0/0/0/0
R1Gi0/0/0/110.0.15.1/30R5 Gi0/0/0/1
R2Loopback010.255.0.2/32
R2Gi0/0/0/010.0.12.2/30R1 Gi0/0/0/0
R2Gi0/0/0/110.0.23.1/30R3 Gi0/0/0/0
R3Loopback010.255.0.3/32
R3Gi0/0/0/010.0.23.2/30R2 Gi0/0/0/1
R3Gi0/0/0/110.0.34.1/30R4 Gi0/0/0/0
R4Loopback010.255.0.4/32
R4Gi0/0/0/010.0.34.2/30R3 Gi0/0/0/1
R4Gi0/0/0/110.0.45.1/30R5 Gi0/0/0/0
R5Loopback010.255.0.5/32
R5Gi0/0/0/010.0.45.2/30R4 Gi0/0/0/1
R5Gi0/0/0/110.0.15.2/30R1 Gi0/0/0/1

What you’ll practise

  • Explain P-space and Q-space on a ring
  • Enable TI-LFA per interface on IOS XR
  • Read a repair path and its label stack
  • Fail a link and follow the path traffic takes
  • Choose node protection with a tiebreaker

The tasks

  1. Why a ring is the hard case
  2. Enable TI-LFA
  3. Read the repair path
  4. Fail the link
  5. Protecting against a node failure

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 TI-LFA - link and node protection5 nodes, 5 links. Every link is listed as text below the diagram.R1R2R3R4R5Gi0/0/0/1Gi0/0/0/0Gi0/0/0/0Gi0/0/0/0Gi0/0/0/1Gi0/0/0/0Gi0/0/0/1Gi0/0/0/1Gi0/0/0/1Gi0/0/0/0
5 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • R1 Gi0/0/0/0 to R2 Gi0/0/0/0
  • R2 Gi0/0/0/1 to R3 Gi0/0/0/0
  • R3 Gi0/0/0/1 to R4 Gi0/0/0/0
  • R4 Gi0/0/0/1 to R5 Gi0/0/0/0
  • R5 Gi0/0/0/1 to R1 Gi0/0/0/1
Nodes in TI-LFA: link and node protection, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
R1Cisco IOS XRvxrv-k9-demo-6.3.11 vCPU, 2,560 MB
R2Cisco IOS XRvxrv-k9-demo-6.3.11 vCPU, 2,560 MB
R3Cisco IOS XRvxrv-k9-demo-6.3.11 vCPU, 2,560 MB
R4Cisco IOS XRvxrv-k9-demo-6.3.11 vCPU, 2,560 MB
R5Cisco IOS XRvxrv-k9-demo-6.3.11 vCPU, 2,560 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 CCNP Service Provider guided labs.

  3. Open 11 - TI-LFA - link and node protection 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 Cisco. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.