All right, let's just do a quick demo of trace routing and exploring some of
these options.
So I have this very basic lab topology with the sequence of routers.
We're going to be able to tell which router is which just based on the last oct
et in the
IP address.
If it's a dot one, it's router one dot three, it's router three and so on and
so forth.
And what I have here is a couple of things.
First of all, we have OSPF running everywhere in here.
However, OSPF is not advertising 11 11 11 11, nor is it advertising four dot WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
However, OSPF is not advertising 11 11 11 11, nor is it advertising four dot
four dot
four dot four.
What I did do was I made sure that router three knows where four dot four dot
four dot four
is based on static routing.
And so with that in mind, let's do a couple of trace routes and see exactly how
this pans
out.
And again, we'll take a look at some of these options.
So first of all, just a basic trace route.
If I were to trace out the IP address that router four knows, one dot one dot
one dot
one, then I can see that it returns a sequence here from router three, router
two and router
one.
It does give me three different probe responses. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It does give me three different probe responses.
It's what we're typically used to seeing out of a traditional trace route.
Well now I could do the same command, but I can say probe two.
And now we see we're only getting a single probe response out of each TTL entry
and I
can even do probe one.
And I just got a single entry out of each one.
And I could already tell it went a whole lot faster.
Furthermore, if I were to say something like probe one and then TTL, now we see
I have
to specify the minimum TTL.
And then after this I'll specify the maximum. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then after this I'll specify the maximum.
So if I were to say, you know, TTL of one and then a maximum of, let's just say
maximum
of two.
So how far did we get?
Well, we started, we got a response out of router three and then we got a
response out
of router two here.
So that's the dot two, but it is not actually getting to the destination
because it ran
out of TTL, my maximum TTL for this operation was two.
So that is the benefit I suppose of setting it lower is if it does get too far WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So that is the benefit I suppose of setting it lower is if it does get too far
into the
network or we get to the point where we're timing out, then we don't have to
wait as
long.
However, I can also interestingly do this where I say TTL of two as the minimum
and
the maximum something like 10.
And notice we start here with router two and then we hit router one, but we
didn't get
a response out of router three.
We only got a response out of router two.
And the reason we got a response out of router two is because the TTL actually WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And the reason we got a response out of router two is because the TTL actually
started at
two instead of one.
So that's kind of a fun thing to explore there.
Lastly, if I were to do a trace route to 11 11 11 11, like we said, that's not
being advertised
into OSPF and therefore router four doesn't know where it is.
So I might get into this situation where it's going, you know, star star star
here.
We're not getting anything.
And I have to wait 30 hops for this.
Well, I can hit control shift six and there we go.
It just broke out of it. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It just broke out of it.
So that's a very useful tool.
I can also do that if I'm pinging.
If I make a mistake and I'm like, Hey, let's do a ping 11 11 11 11.
And maybe I even repeated a hundred times.
I'm like, Oh man, I've got to sit here for a long time.
Yeah, control shift six works out pretty well.
Okay.
And lastly, the source concept.
So let's say I wanted to do my trace route sourcing from this four dot four dot
four
address.
We know router three knows where it is, but we do but router two and router one WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We know router three knows where it is, but we do but router two and router one
have no
awareness.
So let's do our trace route and we'll specify an IP address we can get to.
And then I'm going to also specify my source of four dot four dot four.
And we'll just go ahead and do a probe of one.
So what we get is we get a response from router three because router three
knows how to get
back to four, four, four, four router four is sending this trace route with a
source IP
address of four, four, four, four, and therefore the response from these WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
address of four, four, four, four, and therefore the response from these
devices is going to
be directed to four, four, four, four.
They just don't know where it is.
At least routers one and router and routers one and two do not know how to get
back.
And so we got a response out of router three, but not out of routers two and
one.
And this is going to go until the max of 30, which is why we'd want to break
out.
So this is just a fun way to explore trace route options.
Again, it's so easy just to use a command like this that we use a lot and just
always
use the basic options. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
use the basic options.
Well, use these options to our advantage and using especially the source option
to be
able to make sure certain subnets are reachable is very powerful and making it
so that we're
more efficient with the probe and numeric, which we didn't demonstrate here,
but we can
use that to avoid the DNS lookups that might take us a long time.