Why do some times reported by VisualRoute differ depending on where they are in the trace route?
Depending on the accuracy of the system clock, ‘ms’ numbers can be correct to 5ms – that applies to all programs. But there is a big difference between pinging an address, and having that address appear in the middle of a trace route. The difference is: a router which is being pinged has to directly respond to an ICMP packet (ICMP Echo Reply). A router which appears in the middle of a trace route is simply sending an error packet back, telling the sender the packet didn’t get through (ICMP TTL Expired in Transit). The latter is considered low priority and so the router put it to the bottom of its ‘to-do’ list, ensuring that higher-priority tasks are completed first. That is the cause of the extra delay.
Related Questions
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