Cisco CCNA Packet Tracer Ultimate labs: PPP & PPP CHAP: Answers Part 4

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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 to complete the bonus tasks, we need to create a DHCP pool on the customer routers to allocate IP addresses to their PCs.

In the relevant subnets, we need to configure the customer routers with NAT so that the PCs can access the Internet. And we need to verify that things are working by making sure that PC 1 and PC 2 can ping

So on Customer Router 1
show ip interface brief
no IP address is configured on gigabit 0.0.0 so we need to go on to that interface. Configure an IP address of mask and no shut the interface.

So show ip interface brief
now shows us that interface is up, up and it’s configured with this IP address.

So let’s configure a DHCP pool
So ip dhcp pool
I’m going to give it a name of PC. You could call this anything in the exam, follow the instructions in the question, but here we can configure it with any name PC is fine for this example.

Network that we’re going to configure is with a /24 mask. Default gateway or default router will be the local router, DNS server will be
So don’t forget to configure the DNS server in your DHCP pool.

Now that’s configured. Let’s verify that the PC gets an IP address. So on the PC’s configuration; I’m going to configure it to use DHCP.

Go to desktop, command prompt type, ip config
We can see that an IP address has been allocated to the PC.
Back on the router, notice we see that there was an address conflict for that IP address.
So the IP address that was allocated to the PC is this.

Now you could have created a DHCP excluded range and excluded IP addresses in a specific range. That would force the router to allocate IP addresses starting at 11.
But in this example, it’s worked without that configuration. The router did a ping and saw that it had this IP address, so it allocated the next IP address in the range.

So that looks good. The PC will hopefully be able to ping the router which it can.
But it won’t be able to ping at this point because we need to configure NAT on the router.

So on Customer Router 1, interface serial 1/0
This is going to be our NAT outside interface. ……

  • David Bombal