Packet Drop between end to end Topology

Hi All,
How to find the packet drop has been occurring(leakage) even neighborship has formed successfully in MPLS(L3VPN) topology.
It would be help to pin down where it occurred. we knew it will happen due to some IOS XR code issue with appropriate feature such as Multicast, hardware, and BGP but how to find out exact portion of issue and highlight with Dev team.

I have explored MPLS technology through Network lessons alone and got many more appreciating in my organization. Thank you for all your relentless efforts.


Hello Shakil

If I have understood correctly, you are experiencing lost packets in some of your communications over an MPLS L3 VPN topology, correct? But you can’t find where those packets are being dropped. There are several ways that you can troubleshoot this, but not all methods will work in all situations. it depends upon the nature of the packet drop. These are some guidelines that may be able to help you:

  • Ping and Traceroute: These are basic tools that can help identify if there’s a problem along the path. Use them to check the connectivity between different points in your network. You can also see with traceroute the specific location at which your communication fails. At least this is the case for the overlay network.
  • MPLS LSP Ping/Traceroute: This is similar to the regular Ping and Traceroute, but it’s MPLS-specific. It allows you to check the connectivity of your Label Switched Paths (LSPs).
  • Show commands: There are several useful show commands in IOS XR like show mpls forwarding, show mpls ldp neighbor, and show bgp vpnv4 unicast summary. These can provide useful information about the state of your MPLS and BGP sessions.
  • Syslog and SNMP: These tools can provide real-time information about your network. You can set up alerts for specific events like a change in the BGP state, high CPU usage, etc.
  • NetFlow: This is a more advanced tool that can provide detailed information about the traffic in your network. It can help identify patterns and trends that might be causing packet loss.

I believe the most information can be gained from your logs (syslog/snmp) or from an implementation of Netflow. But this depends upon the access you have to the MPLS part of the network. Is this provided by your ISP or are you managing the MPLS network? If it is the latter, ti would be easier to identify the specific problem areas.

Remember, the issue might not be caused by a single factor. It could be a combination of several factors like a software bug, a hardware issue, a configuration mistake, etc. So, it’s important to check everything.

Let us know how you get along.

I hope this has been helpful!


Thank you for detailed clarifications.

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