ccna 1- cisco networking academy

ccna 1- cisco networking academy.Barney(verified (verified)Q. .......................... .A Figure 12-14 CHAP Validation ProtocolThe authentication flow when authentication begins to work is shown in Figure 12-13 and Figure 12-14. If it is unsuccessful (for example, if the passphrase does not match), then another final message flows out. In addition, if authentication fails, PPP sets the interface state to up/down, and the router cannot forward and receive frames from that interface.The PAP message flow is much less secure than CHAP because PAP sends the host name and password in plaintext in the message. This information can be easily read if someone places a tracking tool in the circuit. CHAP, on the other hand, uses a one-way hashing algorithm, called Message Digest 5 (MD5) O plus a shared random number, and the passphrase entered into the algorithm is never transmitted on the link.The CHAP process also uses the hash only once, so that a miscreant cannot copy only the hashed value and send it at some future time. This random number is declared in the CHAP challenge message; and the routers at both ends are preconfigured using the passphrase. The router receiving the challenge runs a hashing algorithm using the random number just obtained and the secret passphrase, and returns the result of the operation to the router issuing the challenge. The router that issued the challenge must run the same algorithm using the random number (sent over the link) and the passphrase (not sent over the link). If the result matches, the passphrase must also match. In the future, the next time the authentication process runs, the authentication router generates and uses a different random number.AP and CHAP are a few of the things that PPP's LCP accomplishes. The next topic is concerned with how to configure and verify PPP.PPP ConfigurationCompared to HDLC, configuring PPP requires only one change: use the encapsulationppp command on both ends of the link. With HDLC, other things can be configured as you wish, such as the interface bandwidth and interface description. Of course, the interface must be enabled (enabled,noshutdown) o but the migration configuration from HDLC to PPP simply requires the encapsulation ppping command on both ends of the serial interface.Example 12-4 shows a simple configuration using two routers as shown in Figure 12-11. The example includes IP address configuration, but the IP addresses are not