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Multi-vendor troubleshooting lab 2 of 12

BGP between vendors with differing defaults

Larkfield's four sites run eBGP in a ring, and every session hides a default that one vendor has and the others don't: address families that vanish when you configure one, routes that are never exported, communities that are stripped, and a policy chain that silently rejects the rest.

Run this lab

It needs Lite: its 5 nodes are set to 6 vCPU and 7,424 MB in total. That fits the free demo too.

In your workspace: Shared, then Multi-vendor interoperability and troubleshooting guided labs, then 02 - BGP between vendors with differing defaults

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Level
Intermediate
Time
About 75 minutes
Nodes need
6 vCPU, 7,424 MB
Smallest plan
Lite

The scenario

Larkfield is replacing OSPF between its sites with eBGP, one private AS per site. Goole's traffic to Hull should go through the data centre, not Leeds, because that path has the bigger circuit. Hull's SRX tags its routes with community 65020:200 to say so, and the MikroTik at Goole gives routes with that tag a local preference of 200 when they arrive from the data centre.

Nobody can say why half the sessions carry nothing. Each session in the ring hides a default that exists on one vendor only.

DeviceASInterfaceAddressPeer
R165010Gi0/010.0.12.1/30SRX1
R165010Gi0/110.0.41.1/30CHR1
R165010Loopback010.255.0.1/32Advertised
SRX165020ge-0/0/0.010.0.12.2/30R1
SRX165020ge-0/0/1.010.0.23.1/30EOS1
SRX165020lo0.010.255.0.2/32, 10.20.0.1/24Both advertised, with community 65020:200
EOS165030Ethernet110.0.23.2/30SRX1
EOS165030Ethernet210.0.34.1/30CHR1
EOS165030Loopback010.255.0.3/32Advertised
CHR165040ether110.0.34.2/30EOS1
CHR165040ether210.0.41.2/30R1
CHR165040ether310.40.0.1/24Goole LAN, advertised
CHR165040loopback10.255.0.4/32Advertised
H1eth010.40.0.10/24Gateway 10.40.0.1

What you’ll practise

  • Read BGP session state and capabilities on IOS, Junos, EOS and RouterOS
  • Fix a session where Junos stopped negotiating IPv4 because another family was configured
  • Explain what each vendor advertises by default, and write a Junos export policy
  • Find which vendors send communities by default and turn it on where needed
  • Explain the default end of a RouterOS filter chain and repair a chain
  • Prove a design that depends on a community, end to end

The tasks

  1. Give H1 its address
  2. Read every session
  3. SRX1 to R1, the family that vanished
  4. SRX1 to EOS1, nothing to export
  5. EOS1 to CHR1, the missing community
  6. CHR1 to R1, the end of the chain
  7. Prove the design

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 between vendors with differing defaults5 nodes, 5 links. Every link is listed as text below the diagram.R1SRX1EOS1CHR1H1ether3eth0ge-0/0/1Ethernet1ether2Gi0/1Gi0/0ge-0/0/0Ethernet2ether1
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 SRX1 ge-0/0/0
  • SRX1 ge-0/0/1 to EOS1 Ethernet1
  • EOS1 Ethernet2 to CHR1 ether1
  • CHR1 ether2 to R1 Gi0/1
  • CHR1 ether3 to H1 eth0
Nodes in BGP between vendors with differing defaults, 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
SRX1Juniper vSRX NextGen templatevsrxng-23.4R2-S3.92 vCPU, 4,096 MB
EOS1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
CHR1MikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
H1Alpine 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 Multi-vendor interoperability and troubleshooting guided labs.

  3. Open 02 - BGP between vendors with differing defaults 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, Cisco, CompTIA, Fortinet, HPE, Juniper Networks and MikroTik. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.