Troubleshooting MCR When a BGP Session is Down

When a BGP session on Megaport Cloud Router (MCR) is down, step through these troubleshooting actions.

Troubleshooting actions

Action Steps
Verify the BGP configuration Check the ASN, BGP IP address, and subnet mask:
  1. Select the MCR.
  2. Select the VXC and select MCR A-End or B-End.
  3. Under BGP Connections, verify that the correct local ASN is in use for the A-End of the VXC.
  4. Verify that the correct peer IP address is in use.
Verify access to TCP port 179 BGP neighbors establish a TCP session using TCP port 179.
  1. Make sure that a BGP neighbor is not blocking ingress or egress from TCP port 179 and other relevant ephemeral ports. You can view the port number using Wireshark, debug ip packet detail command, netstat in Windows.
  2. Make sure that all firewalls and ACLs permit TCP port 179 in both directions.
Verify the route filtering The MCR Looking Glass displays the routes received or sent after applying route filtering. For details, go to Viewing Traffic Routing Through MCR Looking Glass.
  1. Choose Tools > MCR Looking Glass.
  2. Select an MCR from the MCR drop-down list.
  3. Next to the VXC, click Neighbour Routes.
  4. After Show, select the Advertised or Received tabs to narrow the list.
Check the BGP neighbor state When BGP is configured with a neighbor IP address, it goes through several stages before it reaches the Established state. The BGP Neighbor States are Idle, Connect, Active, OpenSent, OpenConfirm, and Established.

BGP Neighbor States
Check the BGP message type BGP packets use these message types:
  • OPEN – Sets up and establishes BGP adjacency.
  • UPDATE – Advertises, updates, or withdraws routes.
  • KEEPALIVE – Ensures that the BGP neighbor is still alive.
  • NOTIFICATION – Indicates an error condition to a BGP neighbor.
Verify the MD5 authentication
  • Look through the logs for Invalid MD5 digest.
  • Verify that the correct BGP MD5 password is in use for the A-End and B-End of the VXC.
Run connectivity tests
  • Run a ping test between BGP peers.
  • Confirm the ARP table entry of the BGP peer.
Find error conditions in BGP logs The BGP protocol sends a notification message when it detects an error with the BGP session such as: an expiring hold timer, a change to neighbor capabilities, or a request to reset a BGP session. When an error is detected, the BGP session is closed.

For example, enter show log %BGP-xxxxx

Next steps

If the troubleshooting actions do not resolve your issue, contact support. Before contacting support for assistance, collect the following information.

  • Note the date, time, and time zone in which the issue started.
  • Is the BGP session down?
  • Is the BGP session flapping? For example, does the peering establish, then drop, re-establish, and then drop? Try to pinpoint where the problem might be in the network using ping.
  • Is there a BGP routing issue?

Collect the following required data

BGP configuration information:

  • Interface settings, including VLAN number
  • BGP IP address and subnet mask
  • BGP ASN
  • BGP network addresses to be advertised
  • BGP neighbor IP address and subnet mask
  • BGP neighbor ASN
  • BGP neighbor network addresses to be received
  • BGP authentication between BGP peers
  • BGP route filtering and manipulation, if any

BGP command output and packet capture information:

  • Examine the BGP neighbor table and BGP state using the show IP BGP summary command
  • Examine the BGP neighbor details using the show IP BGP neighbors command
  • Logs that show BGP-related messages (output from the show log %BGP-xxxxx command)
  • BGP routing table entries that have BGP routing issues (output from the show IP BGP command)
  • BGP advertised routes (output from the show IP BGP neighbors <neighbor-ip-address> advertised-routes command)
  • BGP received routes (output from the show IP BGP neighbors <neighbor-ip-address> routes command)
  • Routing table (output from the show IP route <ip-address> command)
  • Traceroute logs between source and destination host
  • Packet capture logs, if possible (file size can be up to 10 M)

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