Cisco CCNA Packet Tracer Ultimate labs: PPP & PPP CHAP: Answers Part 3

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The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-protocol datagrams over point-to-point links. PPP is comprised of three main components:

● A method for encapsulating multi-protocol datagrams.
● A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection.
● A family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols.

The Challenge Handshake Authentication Protocol (CHAP) (defined in RFC 1994) verifies the identity of the peer by means of a three-way handshake. These are the general steps performed in CHAP:

After the LCP (Link Control Protocol) phase is complete, and CHAP is negotiated between both devices, the authenticator sends a challenge message to the peer.

The peer responds with a value calculated through a one-way hash function (Message Digest 5 (MD5)).

The authenticator checks the response against its own calculation of the expected hash value. If the values match, the authentication is successful. Otherwise, the connection is terminated.

This authentication method depends on a “secret” known only to the authenticator and the peer. The secret is not sent over the link. Although the authentication is only one-way, you can negotiate CHAP in both directions, with the help of the same secret set for mutual authentication.

For more information on the advantages and disadvantages of CHAP, refer to RFC 1994

So in Customer Router 1
show ip route
at the moment shows us that we only see connected and local routes on the routing table.
So ip route default route looks like this.
Next hop is going to be

So show ip route
now shows us that we’ve got the default route in the routing table.
We now need to ping the Google DNS server which is

So ping
let’s see if that works, yes it does. So that’s good.

We also need to ping but that means we need to configure the main server to be the DNS server. So and hopefully now we’ll be able to ping which we can.

In this packet tracer lab it’s resolving to the same IP address as the Google DNS server. But that’s ok. It proves that we’ve successfully configured things properly in our lab. I’ll save my configuration.

Again for the exam, you’re going to use copy running-config startup-config
For the real world, we’ll use this command because it’s lot shorter.

Something similar needs to be done on Customer Router 2.
So show ip route
no static route is shown in the routing table, no gateway the last resort.
So IP route create a static default route pointing to

So show ip route again
notice the gateway of last resort has been configured. We’ve got a static default route or candidate default route in routing table. So we should be able to ping Google, which we can. Notice we won’t be able to ping because we don’t have a name server configured.

So ip name server ping; that now works.
So we’ve completed the required tasks in this lab.
How did you do?
Were you able to get the lab to work?
Were you able successfully complete the lab?
Now I’m going to show you how to complete the bonus tasks which makes the lab more real world.

  • David Bombal