# There is a number of diagnostic utilities for IP networks, mostly
# based on the ICMP protocol. The most basic of those is ‹ping›,
# which asks another computer whether it's alive. The packets it
# sends are ICMP echo request, and the target host is supposed to
# send an ICMP echo reply back.

# Given no switches, ping will send a packet every second or so,
# forever. But we don't have that much time, so we request it only
# sends 5 and then stops, like this:

ping -c 5 1.1.1.1

# The ‹1.1.1.1› above is an IP address. This one is particularly
# easy to remember -- it's a recursive DNS server operated by
# cloudflare.  Notice the numbers that ping prints: those are
# statistics about how long it took for the packet to get there and
# back (rtt = round-trip time). Notice that it's only a few
# milliseconds -- that means the server is not very far from us.
# Magic is involved (and IP addresses that belong to different
# computers depending on where you are)

# Anyway, to prevent Google getting jealous, let's also ping their
# recursive DNS server, which lives at the address 8.8.8.8 (not as
# flashy as the cloudflare one, but not bad either):

ping -c 5 8.8.8.8

# Let's just round it off with my favourite public recursive
# resolver, ran by Level3, living at the address 4.2.2.2 (I don't
# actually recommend using it for DNS... I just like to ping it):

ping -c 5 4.2.2.2

# That's it for ping (with IP addresses), let's look at ‹traceroute›
# now, which is a little more interesting. The script lives in
# ‹traceroute.sh›.