1. PPP was needed to be able to dynamically assign IP addresses and allow for use of multiple protocols. PPP provides router-to-router and host-to-network connections over both synchronous and asynchronous physical circuits.
2. PPP is the most widely used and most popular WAN protocol because it offers all the following features:
· Control of data link setup
· Provides for dynamic assignment of IP addresses
· Network protocol multiplexing
· Link configuration and link quality testing
· Error detection
· Negotiation options for capabilities such as network-layer address negotiation and data compression negotiations
3. PPP addresses the problems of Internet connectivity by employing three main components:
· A method for encapsulating datagrams over serial links. PPP uses High-Level Data Link Protocol as a basis for encapsulating datagrams over point-to-point links.
· A Link Control Protocol for establishing, configuring, and testing the data-link connection.
· A family of Network Control Protocols for establishing and configuring different network-layer protocols. PPP is designed to allow the simultaneous use of multiple network-layer protocols.
4. What protocols does PPP support?
· IP
· IPX
· Appletalk
5. The fields of a PPP frame are as follows:
· Flag-Indicates the beginning or end of a frame and consists of the binary sequence 01111110.
· Address - Consists of the standard broadcast address, which is the binary sequence 11111111. PPP (does/does not) assign individual station addresses.
· Control - 1 byte that consists of the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. A connection-less link service similar to that of Logical Link Control (LLC) Type 1 is provided.
· Protocol - 2 bytes that identify the protocol encapsulated in the data field of the frame.
· Data - 0 or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the data field is found by locating the closing flag sequence and allowing 2 bytes for the frame check sequence (FCS) field. The default maximum length of the data field is 1,500 bytes.
· FCS - Normally 16 bits (2 bytes). Refers to the extra characters added to a frame for error control purposes.
6. PPP provides a method of establishing, configuring, maintaining, and terminating a point-to-point connection. In order to establish communications over a point-to-point link, PPP goes through four distinct phases:
· Link establishment and configuration negotiation-An originating PPP node sends LCP frames to configure and establish the data link.
· Link quality determination-The link is tested to determine whether the link quality is sufficient to bring up network-layer protocols. Note that this is an optional phase.
· Network-layer protocol configuration negotiation -The originating PPP node sends NCP frames to choose and configure network-layer protocols. The chosen network-layer protocols-such as IP, Novell IPX, and AppleTalk-are configured, and packets from each network-layer protocol can be sent after this phase is complete.
· Link termination -The link remains configured for communications until LCP or NCP frames close the link or until some external event occurs (for example, an inactivity timer expires or a user intervenes).
7. To check LCP and NCP, use the show interfaces command.
8. The authentication phase of a PPP session is optional. If it is used, authentication takes place before the network-layer protocol configuration phase begins. The authentication options require that the calling side (remote host) of the link enter authentication information to help ensure that the user has the network administrator's permission to make the call.
9. When configuring PPP authentication, you can select Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP). In general, CHAP is the preferred protocol.
10. PAP provides a simple method for a remote node to establish its identity, using a two-way handshake. After the PPP link establishment phase is complete, a username/password pair is repeatedly sent by the remote node across the link until authentication is acknowledged or the connection is terminated.
11. PAP is not a strong authentication protocol. Passwords are sent across the link in clear text, and there is no protection from playback or repeated trial-and-error attacks.
12. CHAP is used to periodically verify the identity of the remote node, using a three-way handshake. This is done upon initial link establishment and can be repeated any time after the link has been established. CHAP offers features such as periodic verification to improve security; this makes CHAP more effective than PAP because CHAP requires a challenge before authentication can take place.
13. You can use the same host name on multiple routers-When you want remote users to think they are connecting to the same router when authenticating, configure the same host name on each router.