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CCNP ENARSI lab 17 of 35

BGP path selection: weight, local preference, AS-path prepending and MED

Steer a dual-homed enterprise's traffic in both directions: outbound with weight and local preference, inbound with MED and AS-path prepending, and predict every decision from the BGP best-path algorithm.

Run this lab

It needs Lite: its 5 nodes are set to 5 vCPU and 2,560 MB in total. That fits the free demo too.

In your workspace: Shared, then CCNP ENARSI 300-410 guided labs, then 17 - BGP path selection - weight local preference AS-path prepending and MED

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Level
Advanced
Time
About 80 minutes
Nodes need
5 vCPU, 2,560 MB
Smallest plan
Lite

The scenario

Nightjar Media (AS 64500) owns 203.0.113.0/24 and is connected to two providers: ISP-A (AS 64501) over two circuits, a primary to R1 and a second one to R2, and ISP-B (AS 64502) to R2. Both providers reach the "Internet" (R5, AS 64510), which hosts a video platform (192.0.2.0/24) and a backup service (198.51.100.0/24). All BGP sessions are up, with no policy: today BGP picks paths by its own tie-breakers.

The traffic engineering plan:

  1. Outbound, company-wide: use ISP-A's primary circuit (R1–R3) first, ISP-A's second circuit (R2–R3) second, ISP-B last.
  2. Outbound exception on R2 only: traffic from R2 to the backup service 198.51.100.0/24 must use ISP-B directly (contract reasons).
  3. Inbound from ISP-A: ISP-A should send traffic for 203.0.113.0/24 over the primary circuit.
  4. Inbound from the Internet: everyone should prefer reaching Nightjar through ISP-A rather than ISP-B.
DeviceInterfaceAddressPeer
R1Gi0/1172.16.13.1/30R3 (ISP-A) 172.16.13.2
R2Gi0/1172.16.23.1/30R3 (ISP-A) 172.16.23.2
R2Gi0/2172.16.24.1/30R4 (ISP-B) 172.16.24.2
R1 / R2Lo010.255.0.1 / 10.255.0.2iBGP (next-hop-self)
R1 / R2Lo1203.0.113.1/25 / 203.0.113.129/25public block halves
R5Lo1 / Lo2192.0.2.1/24 / 198.51.100.1/24Internet services

Both R1 and R2 originate 203.0.113.0/24 (a static route to Null0 plus a network statement).

What you’ll practise

  • Walk the BGP best-path algorithm in order and name the deciding step
  • Use local preference for AS-wide outbound policy and weight for one router's exception
  • Use MED to choose between two links into the same neighbouring AS
  • Use AS-path prepending to influence how the rest of the Internet reaches you
  • Verify path choices with show ip bgp, the per-prefix detail and traceroute

The tasks

  1. Read today's decisions
  2. Company-wide outbound preference with local preference
  3. A local exception with weight
  4. Bring ISP-A's traffic in over the primary circuit with MED
  5. Make the Internet prefer ISP-A with AS-path prepending
  6. Verify the traffic

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 BGP path selection - weight local preference AS-path prepending and MED5 nodes, 6 links. Every link is listed as text below the diagram.R1R2R3R4R5Gi0/0Gi0/0Gi0/1Gi0/0Gi0/2Gi0/0Gi0/2Gi0/0Gi0/1Gi0/1Gi0/1Gi0/1
5 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • R1 Gi0/0 to R2 Gi0/0
  • R1 Gi0/1 to R3 Gi0/0
  • R2 Gi0/1 to R3 Gi0/1
  • R2 Gi0/2 to R4 Gi0/0
  • R3 Gi0/2 to R5 Gi0/0
  • R4 Gi0/1 to R5 Gi0/1
Nodes in BGP path selection: weight, local preference, AS-path prepending and MED, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
R1Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 vCPU, 512 MB
R2Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 vCPU, 512 MB
R3Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 vCPU, 512 MB
R4Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 vCPU, 512 MB
R5Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 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 CCNP ENARSI 300-410 guided labs.

  3. Open 17 - BGP path selection - weight local preference AS-path prepending and MED 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.

More CCNP ENARSI labs

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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.