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JNCIS-ENT lab 13 of 17

BGP routing and path selection

Dual-home Ashby Freight to its ISP with two edge routers. You bring up IBGP between loopbacks and authenticated EBGP sessions to the ISP, fix the classic next-hop problem, advertise the company aggregate with a community, and steer traffic both ways with local preference and AS-path prepending.

Run this lab

It needs Standard: its 3 nodes are set to 12 vCPU and 15,360 MB in total.

In your workspace: Shared, then JNCIS-ENT JN0-352 guided labs, then 13 - BGP routing and path selection

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 12 vCPU and 15,360 MB together. Every lab plan includes every guided lab.

Level
Advanced
Time
About 90 minutes
Nodes need
12 vCPU, 15,360 MB
Smallest plan
Standard

The scenario

Ashby Freight (AS 65010) has two internet links to the same provider (AS 64500): a primary link on EDGE1 and a backup link on EDGE2. The ISP router is already configured and is not yours to change: it sends a default route, its monitoring prefix 203.0.113.0/24, 198.18.0.0/15 and its loopback 192.0.2.1/32, and it requires MD5 with the key Ashby-BGP-2026 on both sessions. OSPF already runs between EDGE1 and EDGE2 for their loopbacks and office LANs.

RouterLoopbackISP linkOffice LAN
EDGE1192.168.255.21198.51.100.2/30 (ISP 198.51.100.1)10.65.1.0/24
EDGE2192.168.255.22198.51.100.6/30 (ISP 198.51.100.5)10.65.2.0/24

Policy goals:

  1. Advertise only the company block 10.65.0.0/16 to the ISP, tagged with community 65010:100.
  2. All outbound traffic uses the primary link while it is up.
  3. Inbound traffic should also arrive on the primary link: make the backup path look longer to the ISP.

What you’ll practise

  • Explain BGP sessions, message types and the neighbour state machine
  • Configure IBGP between loopbacks and EBGP to a provider, with groups, peers and MD5 authentication
  • Explain why IBGP routes can be hidden, and fix it with next-hop self
  • Read attributes (AS path, local preference, MED, communities, next hop) and follow the path selection steps
  • Apply import and export policy: advertise an aggregate, add communities, set local preference and prepend the AS path
  • Troubleshoot with show bgp summary, show bgp neighbor and the receive and advertising views

The tasks

  1. BGP in one minute
  2. IBGP between the loopbacks
  3. EBGP to the ISP
  4. The next-hop problem
  5. Advertise the company block with a community
  6. Path selection, local preference and AS-path prepending
  7. Tools for troubleshooting BGP

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 routing and path selection3 nodes and 2 networks, 5 links. Every link is listed as text below the diagram.EDGE1EDGE2ISPOffice-LAN-1Office-LAN-2ge-0/0/2ge-0/0/2ge-0/0/0ge-0/0/0ge-0/0/0ge-0/0/1ge-0/0/1ge-0/0/1
3 nodes and 2 networks, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • EDGE1 ge-0/0/0 to ISP ge-0/0/0
  • EDGE2 ge-0/0/0 to ISP ge-0/0/1
  • EDGE1 ge-0/0/1 to EDGE2 ge-0/0/1
  • EDGE1 ge-0/0/2 to Office-LAN-1 (network)
  • EDGE2 ge-0/0/2 to Office-LAN-2 (network)
Nodes in BGP routing and path selection, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
EDGE1Juniper vJunos-routervjunosrouter-24.2R1-S2.54 vCPU, 5,120 MB
EDGE2Juniper vJunos-routervjunosrouter-24.2R1-S2.54 vCPU, 5,120 MB
ISPJuniper vJunos-routervjunosrouter-24.2R1-S2.54 vCPU, 5,120 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 JNCIS-ENT JN0-352 guided labs.

  3. Open 13 - BGP routing and path selection 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 JNCIS-ENT labs

All JNCIS-ENT labs

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