If you use the 'ping' command in a terminal, how frequently (if ever) do the network paths to/from the destination differ?

What could cause such paths to differ?

  • This is impossible to answer without knowing the network in detail. – Zac67 Sep 17 '18 at 11:43
  • but i take that to mean that the paths can/do differ? – Zach Smith Sep 17 '18 at 12:05
  • Yes. Each packet finds its own path and it may change at any time. – Zac67 Sep 17 '18 at 14:08

For such a general question, the answer is equally general: "they differ quite often".

  • You'll notice it on many-hop routes more often (especially those with multiple parallel routes, such as Europe to Asia)
  • Also any situation where there's asymmetric routing

Asymmetric routing is easy to see on a small scale with a circle of routers each with clockwise default route:

     A -> R1 -> R2
          ^      v
          R4 <- R3 <- B

Arrows show default routes. Ping from A to B will go A->R1->R2->R3->B and the return will be B->R3->R4->R1->A.

Multiple paths are easy to see with routers which have some variety of load balancing:

               /- R2 -\
     A -> R1 -+        +- R4 <- B
               \- R3 -/

If R1 and R4 route to either R2 or R3 depending on the load at a given instant, one packet will go A->R1->R2->R4->B and the next might go A->R1->R3->R4->B.

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