Welcome to Abdul's Support Page

PPP Point-to-Point Protocol

Point-to-Point protocol is a Data Link layer protocol that can be used over asynchronous serial (dial-up) and synchronous serial (ISDN) media and that uses the LCP (Link Control Protocol) to build and maintain data-link connections. The basic purpose of PPP is to transport layer-3 packets over a Data Link layer point-to-point link. PPP consists of two main components, LCP (Link Control Protocol -used to establish, configure, and test the connection) and NCP (Network Control Protocol -configures many different layer protocols).

NCP -A PPP protocol for negotiating OSI Layer 3 (the network layer) parameters.

HDLC -A method for encapsulating datagrams over serial links.

LCP -A protocol that establishes, configures, and tests data link connections used by the PPP Link Control Protocol offers PPP encapsulation different options, including the following:

Authentication -options includes PAP and CHAP

Compression -Data compression increases the throughput on a network link, by reducing the amount of data that must be transmitted. Error Detection -Quality and Magic numbers are used by PPP to ensure a reliable, loop-free data link.

Multilink -Supported in IOS 11.1 and later, multilink is supported on PPP links between Cisco routers. This splits the load for PPP over two or more parallel circuits and is called a bundle.

PPP Session Establishment

Link-establishment phase -LCP packets are sent by each PPP device to configure and test the link. The LCP packets contain a field called the Configuration Option that allows each device to see the size of the data, compression, and authentication. If no Configuration Options are set, then the default config is used. Authentication -If configured, either CHAP or PAP can be used to authenticate a link.

Authentication only takes place before Network layer protocol information is read.

Network layer protocol phase -PPP uses the Network Control Protocol to allow multiple Network layer protocols to be encapsulated and sent over a PPP data link.

Configuring PPP

Router3(config)#int s0

Router3(config-if)#encapsulation ppp

Router3(config-if)#exit

Router3(config)#username Router2password cisco

After you set the encapsulation to PPP, you have to exit to global configuration mode to set the username and password. The username is the hostname of the remote host connecting via PPP on the serial line; the password and encapsulation type must be the same for both routers.

Setting PPP Authentication

PAP-less secure of the two (sends passwords as plain text) and

CHAP -uses a three-way handshake to force remote hosts to identify themselves after the link establishment phase is complete. The local router sends a challenge request to the remote device and the remote device sends a value calculated using a one-way hash function called MD5 (encryption).

Router3(config)# int s0

Router3(config-if)#ppp authentication chap pap

This tells the router to first use CHAP and then go to PAP if CHAP isn't available.

Setting Banners

Syntax:

   Router(config)#banner ?

   LINE            c banner-text c, where 'c' is a delimiting character

   exec            Set EXEC process creation banner

   incoming      Set incoming terminal line banner

   login            Set login banner

   motd           Set Message of the Day banner

Example:

   Router(config)#banner motd #

   Enter TEXT message. End with the character '#'.

   THIS IS THE MESSAGE OF THE DAY BANNER

   #

Disable Banner:

   Router#conf t

   Router(config)#no banner motd

Interface Descriptions

An interface description is limited to 80 characters and typically describes the function of the interface.

   R2(config)#interface serial 1

   R2(config-if)#description Link to East Office