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BGP in depth lab 12 of 14

Troubleshooting BGP sessions

Monday morning at Kestrel Fibre: five BGP sessions are down after a weekend of maintenance, and each one is stuck or failing in a different way. Use the session state, the logs and the TCP details to find five faults, including a session that comes up, then dies, every 15 seconds.

Run this lab

It needs Lite: its 6 nodes are set to 6 vCPU and 4,352 MB in total. That fits the free demo too.

In your workspace: Shared, then BGP in depth guided labs, then 12 - Troubleshooting BGP sessions

Try it free for 30 minutesRun it on Lite from £3 a day

The free demo needs no card and no email. Every lab plan includes every guided lab.

Level
Advanced
Time
About 90 minutes
Nodes need
6 vCPU, 4,352 MB
Smallest plan
Lite

The scenario

You've arrived to five tickets. OSPF is fine, so the loopbacks are reachable. BGP is not.

TicketSessionReported symptom
1R1 to R2, iBGPWon't come up
2R1 to EOS1, eBGPPartner says nothing changed on their side
3R2 to CHR1, eBGPGoes round and round without coming up
4R3 to PEER, eBGP between loopbacksNever tries
5R1 to R3, iBGPComes up, then dies, over and over

Passwords and AS numbers from the design:

ItemValue
Kestrel AS64500
R1 to EOS1 passwordKestrel-Edge1
Timers on R1 to R35 and 15, on purpose
R3 to PEERLoopbacks, across one link
DeviceInterfaceAddressConnects to
R1Loopback010.255.0.1/32
R1Loopback1203.0.113.1/24
R1Gi0/0172.16.1.1/30EOS1 Ethernet1
R1Gi0/110.0.12.1/30R2 Gi0/0
R2Loopback010.255.0.2/32
R2Gi0/010.0.12.2/30R1 Gi0/1
R2Gi0/110.0.23.1/30R3 Gi0/0
R2Gi0/2172.16.2.1/30CHR1 ether1
R3Loopback010.255.0.3/32
R3Gi0/010.0.23.2/30R2 Gi0/1
R3Gi0/1172.16.3.1/30PEER Gi0/0
EOS1Ethernet1172.16.1.2/30R1 Gi0/0
EOS1Loopback010.255.0.10/32
EOS1Loopback1198.51.100.1/24
CHR1ether1172.16.2.2/30R2 Gi0/2
CHR1lan192.0.2.1/24
PEERLoopback010.255.0.30/32
PEERLoopback1198.18.30.1/24
PEERGi0/0172.16.3.2/30R3 Gi0/1

What you’ll practise

  • Say what Idle, Connect, Active, OpenSent, OpenConfirm and Established each tell you
  • Find update-source, multihop and reachability faults
  • Find MD5 mismatches from the log
  • Read a BGP notification for a wrong AS number
  • Recognise a path MTU black hole, and fix it at the cause

The tasks

  1. Read the states
  2. Ticket 1
  3. Ticket 2
  4. Ticket 3
  5. Ticket 4
  6. Ticket 5

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 Troubleshooting BGP sessions6 nodes, 5 links. Every link is listed as text below the diagram.R1R2R3EOS1CHR1PEERGi0/2ether1Ethernet1Gi0/0Gi0/1Gi0/0Gi0/1Gi0/0Gi0/1Gi0/0
6 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • EOS1 Ethernet1 to R1 Gi0/0
  • R1 Gi0/1 to R2 Gi0/0
  • R2 Gi0/1 to R3 Gi0/0
  • R2 Gi0/2 to CHR1 ether1
  • R3 Gi0/1 to PEER Gi0/0
Nodes in Troubleshooting BGP sessions, 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
EOS1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
CHR1MikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
PEERCisco 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 BGP in depth guided labs.

  3. Open 12 - Troubleshooting BGP sessions 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, 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.