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ping checks if you can reach a host and how long the host took to reply


output: ... time=253ms...

Australia is 17,000 km from me. at the speed of light it’s still far!

ping works by sending an ICMP packet and waiting for a reply

ping: to: hello! I’m here!

myth: if a host doesn’t reply to ping, that means it’s down

Some hosts never respond to ICMP packets. This is why traceroute shows “…” sometimes.

ping: hello!
host (thinking): not listening!!

traceroute tells you the path a packet takes to get to a destination

me → my ISP → NYC → Sacramento → Australia

example traceroute

$ traceroute
1: 3ms ← router 12 ms ← ISP
8: NYC4. ALTER.NET 24 ms ← here the packet crossed the USA! from NYC- Sacramento!
9: SAC1.ALTER.NET 97 ms
16: 253ms ← crossing the US takes time


like traceroute, but nicer output! try it!

last panel

look up how traceroute works (using TTLs!) it’s simple + cool!

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