Troubleshooting IX With a BGP Session Routing Issue

When a Border Gateway Protocol (BGP) session on Internet Exchange (IX) is experiencing a routing issue, step through these troubleshooting actions.

Tip

Megaport operates a public, web-accessible MegaIX Looking Glass for peers and network operators to investigate the current routing state. You can query the primary and redundant route servers for live BGP data here: MegaIX Looking Glass.

Troubleshooting actions

Action Steps
Verify the BGP configuration Check the ASN, BGP IP address, and subnet mask.
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, the debug ip packet detail command, or netstat in Windows.
  2. Make sure that all firewalls and ACLs permit TCP port 179 in both directions.
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 the A-End PE router and the B-End PE routers that are connected to route servers to test multilateral peering.
  • Run a ping test between the A-End PE router and the B-End PE router that is connected to bilateral peer to test the bilateral peering.
  • Ask the customer run a ping test from their BGP router to the BGP neighbor IP addresses to test end-to-end connectivity.
  • 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.

For details, see Internet Exchange Overview.

Next steps

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

  • All troubleshooting steps taken, in detail. For example, if you place loopbacks, note their location and direction.
  • 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 applicable)

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) at both ends
  • Traceroute logs between source and destination host
  • Packet capture logs, if possible (file size can be up to 10 M)

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