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MikroTik MTCINE lab 4 of 12

BGP path selection with two upstreams

Fernvale buys transit from two carriers on different terms. Use local preference to steer outbound traffic, MED to choose between two links into the same upstream, and AS-path prepending to make the second carrier a backup for inbound traffic, and read the attributes that decide each best path.

Run this lab

It needs Lite: its 4 nodes are set to 4 vCPU and 1,024 MB in total. That fits the free demo too.

In your workspace: Shared, then MikroTik MTCINE RouterOS v7 guided labs, then 04 - BGP path selection with two upstreams

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Level
Advanced
Time
About 75 minutes
Nodes need
4 vCPU, 1,024 MB
Smallest plan
Lite

The scenario

Fernvale now has two transit contracts with different terms:

  • Northgate (AS 64510) is flat-rate, with a 10G link to EDGE1 and a 1G backup link to EDGE2. Fernvale wants all outbound traffic to use Northgate, and Northgate to send traffic into Fernvale over the 10G link.
  • Eastbridge (AS 64511) bills every gigabyte, in both directions. It should carry traffic only if Northgate fails.

The sessions are already up, so BGP is choosing paths with its defaults. Northgate and Eastbridge also peer with each other, as real carriers do, so every prefix is reachable more than one way.

RouterASAddresses
NORTHGATE64510203.0.113.1/30 (EDGE1) · 203.0.113.5/30 (EDGE2) · 192.0.2.10/30 (Eastbridge) · 198.18.0.1/24
EASTBRIDGE64511192.0.2.1/30 (EDGE2) · 192.0.2.9/30 (Northgate) · 198.18.2.1/24
EDGE164500lo 10.255.255.1 · 203.0.113.2/30 · 10.0.12.1/30 · lan 198.51.100.1/25
EDGE264500lo 10.255.255.2 · 203.0.113.6/30 · 192.0.2.2/30 · 10.0.12.2/30

What you’ll practise

  • Walk the BGP best-path order on RouterOS 7 and find the attribute that decided a route
  • Steer outbound traffic for the whole AS with local preference
  • Choose between two links into one neighbouring AS with MED
  • Make a link backup-only for inbound traffic with AS-path prepending

The tasks

  1. Read the decision BGP made
  2. Prefer Northgate for outbound traffic with local preference
  3. Bring Northgate's traffic in over the 10G link with MED
  4. Make Eastbridge a backup for inbound traffic with AS-path prepending
  5. Explain each decision

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 with two upstreams4 nodes, 5 links. Every link is listed as text below the diagram.NORTHGATEEASTBRIDGEEDGE1EDGE2ether1ether1ether1ether2ether3ether2ether2ether3ether2ether1
4 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • NORTHGATE ether1 to EDGE1 ether1
  • NORTHGATE ether2 to EDGE2 ether1
  • NORTHGATE ether3 to EASTBRIDGE ether2
  • EASTBRIDGE ether1 to EDGE2 ether2
  • EDGE1 ether2 to EDGE2 ether3
Nodes in BGP path selection with two upstreams, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
NORTHGATEMikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
EASTBRIDGEMikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
EDGE1MikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
EDGE2MikroTik RouterOSmikrotik-7.14.21 vCPU, 256 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 MikroTik MTCINE RouterOS v7 guided labs.

  3. Open 04 - BGP path selection with two upstreams 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 MikroTik. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.