folks, I have configured or I have created a very simple topology. You have rather one connected on s 000
The I P addresses on these interfaces are
If I say do show i p interface grief.
Router one has an I p. Address of 201 11
and router to has an i p. Address off.
Unfortunately, I've named this router one also. Let's change the name to our two.
So router to has an I p address of
If you look at the interface itself under my running config,
you see that I've assigned the mask of 2 52 to 55255255252
or slashed 30 which is supposed to be used on point to point links.
If I look at my interfaces show i n t
first thing, you will see that serial 000 is up and line protocol is up and it's connected.
And you also see that the default encapsulation type on my cereal interfaces high level data link, clear control or h D l C.
Let's try and bring across from matter 12 router to and make sure absolutely sure that we can connect. We can ping.
So I'm sitting on rather one
I'm gonna paying 201 12 and we are pinging.
Now let's go ahead and see what happens when I changed encapsulation type
Now, Before I do that, let me show you the routing table over outer one
Now you see, the only the only connection or the only row showing up
on Router one is my 201 10 network, which is directly connected to serial zero, and rather too, would show the same.
Now, let's go ahead and change the encapsulation type
to P p. Pee with command encapsulation. We do a question mark. Three options. We have seen its TLC.
We're going to try and attempt to change the PPP
and then later on will discover and explore for him. Really?
So encapsulation PPP enter
and I got a message saying that line protocol on interface yield 000 has changed too Down
we look at our interface brief.
You see that the line protocol stays down, status stays up. So lair one stays up, but later to stays down.
The reason being that at the other end of the link on router to we still have not changed. Encapsulation two ppp
so router to being HDL see on serial 000 and rather one being PPP
on serial 000 creates a mismatch encapsulation type on the two ends
which takes the link to up down
If we go ahead and go into serial 000 on Router two and change the encapsulation to P P pee, you immediately see that the line protocol on interface 000 has gone to up.
If I look at my interface brief
Do show i p i n t brief
and you see that we are up up now
by paying to the other side
201 11 me right now being on router to So I'm gonna ping rather one
Now let's go take a second look at our I p routing table on route or one.
So if I execute the command, do show i p route
we see a secondary route that has been sold
in our routing table.
Now PPP automatically installs Ah, host route. And if you remember, our host route is a route with a slash 32 masks
to the opposite end of the link.
This is called a pair neighbor out and this is a function of P p. P.
This got automatic me installed in our routing table. Once we changed the encapsulation two PPP,
this is default PPP behavior. So I have a direct route
to the 201 1 to address on Router One. And if I check on router to you will see a direct route to the 201 11 address
on router chew with this last 30 to mask. And here it is.
Once again, this is called appear neighbor out and this is default PPP behavior.
remember I said that PPP can perform authentication
between two devices so that each device can authenticate the other and make sure that the device talking to us is who they say they are.
Well, there are two protocols that PPP uses. Fourth indication,
we're going to cover is password authentication protocol
So if I execute the command
and execute the help feature, you see that they are two protocols
that control authentication over PPP links or point to point protocol links.
The 1st 1 we're gonna cover is Pat
Pap sends the password or the over the link in clear text,
However, it is part of our c, c and s. So we're gonna cover it anyways.
Now, what is going to happen is one side
off the link router one is going to be the authenticator,
and the other side router to is going to be the attentive Katie.
So if your outer one is going to be the authenticator
first we need to have a date. Abi's against which router one can authenticate route or two.
We create this database locally
by executing the command
user name and then the host name off our two router to which is
lower case our troops.
So I simply typing are too.
And then with a question mark command, I see this option password.
So I'm going to create a password that router to must match with rather oneto authenticate itself
password. We're gonna leave the password as or create a password saying Cisco to the password being Cisco.
Next, I'm going to log into the interface or going to interface serial 000 off rather one. And tell Roger one that it is going to be the authenticator by executing the PPP
And then since we're doing pap or password authentication protocol, remember,
password authentication protocol sends the password over the link in clear text.
Now, Router one is trying to authenticate router to
at this point, if I look at my link
with the show I P interface brief command,
you will see that the link has gone up down.
and debug PPP packets.
You will see the PPP is sending back package back and forth or trying to at least authenticated router one. But at this point,
PPP is unable to attend to Kate.
Rather, one is unable to attend decayed router to sew. The link has not gone up yet.
As you see, the link control protocol state is open, but the link is still down.
If we go on router to the authentic 80
and go into interface 000 which is connected to a router one
authentication or PPP Actually PPP
pap, since we're using pap
or password authentication protocol,
then sent user name.
And the username we're sending is our hosting,
Then the password, the password that we send here and the user name that we sent here must match the database that we created on Router One. Namely,
and I look in my running config
If you look I created a user name for our our router to as our two and the password Cisco.
When rather too tries to attend Tecate itself with rather one this host name and this password must match
to what rather one has in its database. The database for us is just one line. This could be many more lines if there were other outers.
So we go back into a round or two.
Well, let me go ahead and turn the authentication on. I mean debugging on another one. So we see something debug PPP
indication and debug PPP events,
and we say ppb Paps and use the name are two password
At this point, the link you see came up
that router one finally got the user name
are two and pass Francisco from Router to and it attended gated route or two.
And you established your connection.
You finish the LCP phase and the connection is up
the interface came up.
If you if I look at my show, I'd be into face brief command again. You will see
mind two faces up and up and I should be able to paying 201 1 to that being rather too.
Next, we're going to explore chap.