Hi All,


I thought I’d post a great resource that explains troubleshooting with Traceroute/ICMP when trying to understand what’s going on when accessing various servers and services.


ICMP Prioritisation


Modern routers have distinct processing paths, the processing path which handles ICMP generation is typically handled by the low powered generic CPUs in the router, and is not prioritised.  ICMP can also be influenced by spikes in CPU usage, so loss can be caused by a spike in other control traffic handled by the generic CPU (e.g. BGP churn) and not a problem with fast path hardware based traffic forwarding.


ICMP generation is NOT a priority for the router – It’s an indication of response times, however not a definitive one.


If you’re not sure if the results you’re seeing are the result of congestion or something similar, then I would suggest you have a read of this great presentation from North America Network Operators Group on interrupting traceroute results.