How can I detect the mininet command line have executed "pingall" command?

[ZackyYoung]

When all the host don't have arp cache, "pingall" will make all hosts send an arp packet to the controller, then I can print shortest paths between two of them. However, after first "pingall", there are arp cache in all hosts, so when the second time mininet executes "pingall" they will not send arp packets to controller, so then how can I know after the second or more "pingall" and print all the shortest path?
It is especially aimed to test the reachability after dynamically adjust the topology.

[EricLee543]

我刚刚确认了在没有改变网络拓扑结构的时候使用pingall 不会发送arp packet。但拓扑发生变化后受影响的host相互ping 似乎还会发送arp packet（待确定）。不过为了简化流程，我建议在拓扑发生改变时（拓扑改变相关的event 被触发后）直接打印出任意两个switch之间的最短路的长度。然后再用ping指令证明连通性即可。针对这个问题我会在明天放出的文档（关于如何检查project）中说明。

I just confirmed that using "pingall" does not trigger ARP packets when there is no change in the network topology. However, after a change in the topology, the affected hosts seem to trigger ARP packets when pinging each other. Nevertheless, to simplify the process, I suggest that upon a change in the topology (after the event related to the topology change is triggered), we directly print the shortest path length between any two switches. Then, we can use the "ping" command to demonstrate connectivity. I will address this issue in the documentation I will release tomorrow regarding how to perform project checks.