[VIDEO PLAYBACK]
- Dot com and DNS does that conversion.
Even more dynamically
than the old school.
[END PLAYBACK]
DAVID MALAN: So these demos I love.
But they are admittedly a little
hard to do sometimes technologically.
Using traceroute, NSLookup,
Kang, or a few other command
line tools on Linux, Mac OS, or Windows.
Traceroute especially, I think it's
just been so eye opening for myself,
back in the day and so
many students since.
When you actually trace
the route between a place
like Harvard and maybe MIT, Stanford,
or cnn.co.jp across the Pacific Ocean.
Because you really see the
increased latency in the hops
that are actually
traveling through an ocean.
Or just down the road in this case.
DOUG LLOYD: Yeah, it really is eye
opening to actually see those hops
and take away.
It's not just one machine
talking to another.
It's got to go through a lot of
different things along the way.
The unfortunate thing, with
an example like traceroute,
is that it's often blocked.
It gets shut down.
DAVID MALAN: You either see a
whole bunch of stars or asterisks
on the screen.
Or it just doesn't give you
back correct information.
In fact on CS50 IDE because of the
cloud infrastructure is running on,
it's not enlightening.
So I'm doing a little bit
of cooking show magic here.
Where usually the
terminal window I'm using
is actually connected to another
server where it's not blocked.
So I can simulate what's going on.
Just because it's so
visually compelling.
But it's a lot harder for students
or teachers in their own schools
to replicate that demo without
a bit of advance prep work.
DOUG LLOYD: But with teachers
who maybe have Mac computers,
it is something that you
can do in the Mac terminal.
DAVID MALAN: It is and Windows too.
It's just traceRT instead of route.
DOUG LLOYD: So it's
definitely possible to do it.
It would be cool if students could also
do it pretty easily from their IDEs.
DAVID MALAN: I agree.
This is a minor enhancement
I've done in recent years.
Dash Q1 sends just one
query instead of three.
Because it was an FAQ as
to why there are three
numbers for every row on the screen.
DOUG LLOYD: Over the times?
DAVID MALAN: Yeah and it's just meant
to give you a visual average of things.
Or just a few numbers you can
lump together and average.
But it was just a distraction.
And it also frankly,
just makes the text wrap,
especially when the fonts
are a little bigger.
So I tried to simplify it
a little bit like this.
But it's great fun because
this is Harvard specific now.
But having students
at Harvard, at least,
see familiar phrases like SC for
Science Center or GW for gateway.
Which we introduce here.
Or NOCS for Northern crossroads.
Or better yet, is when
you start to see things.
In this case, of course,
we're not seeing it.
Sometimes you see airport codes
in the name of the domains.
DOUG LLOYD: Yep.
DAVID MALAN: Which hint at
what city-state they're in.
DOUG LLOYD: In fact, we have
had an example in the past
where we have spoken to Yale.
We've tapped into Yale.
Which I think somehow gets
routed through JFK airport.
Even though it's past--
DAVID MALAN: It might
not be the airport.
DOUG LLOYD: The airport for that area.
That overshoots New Haven a
little bit from Cambridge.
DAVID MALAN: But there's
good opportunities too here.
They're pretty non-deterministic
every time we run this.
Whereby that last hop took far
fewer milliseconds than the second
to last hop.
Even though each of these is supposed
to be from point A to point I plus one,
so to speak.
They're not cumulative.
But that just hints at the
variability in routers, buffers,
in any congestion there might be,
or need to retransmit or so forth.
So it captures some
real world realities.
DOUG LLOYD: Particularly dramatic
when you're crossing an ocean
and you only have a couple
of cables that you can use.
And all the traffic is
trying to get through them.
DAVID MALAN: That's my favorite.
When you actually see a jump
of 100 more milliseconds.
Suggestive that there's
something big in the way.
DOUG LLOYD: But it's
still pretty amazing
that you can get to the other
side of the world so fast.
DAVID MALAN: I tell people that we
have trans Atlantic, trans Pacific
cables underneath the ocean.
It still blows my mind.
