Chapter 3 -- PPP

PPP – A continuation of CCNA – Semester 4

DataLink (Layer 2) TCP/IP Protocols

• SLIP - SLIP is a standard protocol for point-to-point serial connections, using TCP/IP.

• SLIP was a predecessor of PPP.

• PPP - PPP provides router-to-router and host-to-network connections over synchronousand asynchronous circuits, which can be either dialup or leased lines.

PPP Supports

• Protocols – TCP/IP, AppleTalk, IPX

• Essential features such as dynamic address allocation, PAP authentication, CHAP authentication, and Multilink PPP

HDLC

• High-Level Data Link Control (HDLC) is the default encapsulation for ISDN and serial interfaces on a Cisco router. Although HDLC is a default encapsulation, Cisco's HDLC is not necessarily compatible with other vendors' HDLC implementations

• PPP is a standard protocol – can be used with any vendor equipment

PPP Specifications

• It is a standard – operates at OSI Layer 2• Encapsulates Layer 3 datagrams with a specialized

frame. • PPP defines the Link Control Protocol (LCP)• Once the LCP establishes the Layer 2 connection,

the Network Control Protocol (NCP) takes over– frame includes protocol field– Each Layer 3 protocol has its own NCP. For example,

IP's NCP is IPCP; IPX's NCP is IPXCP, and Appletalk's NCP is ATALKCP

Code

• RTA(config)#interface async 2

• RTA(config-if)#encapsulation ppp

Remote Connections

• Exec– Can dial in and take control of command line

• Telnet

• Access resources – network access– Can access printers, servers, etc.

• PPP encapulation via asynchronous dialup connection

Commands

• RTA(config)#interface async 1• RTA(config-if)#encapsulation ppp• RTA(config-if)#async mode interactive • RTA(config)#line 1 • RTA(config-line)#autoselect ppp during-login

– Will eliminate possibility of Exec session

• Router(config-if)#async mode dedicated – Will ensure PPP runs on specified line

Programming Interface

• RTA(config)#interface async1• RTA(config-if)#ip address10.1.1.1 255.255.255.0 or• RTA(config-if)#ip unnumbered lo0 192.16.1.1• RTA(config-if)#peer default ip address 10.1.1.1

– Assigns an address (usually host on same subnet) to the dial-in unit or

• RTA(config-if)#peer default ip address pool NAME– Requires global command # ip local pool pool-name

starting-address end-address.

LCP Configuration Options

• Authentication– CHAP or PAP

• Callback– Billing consolidation

• Compression– Reduces size of frame - Stacker, Predictor, and

Microsoft Point to Point Compression (MPPC)

• Multilink PPP– load balancing functionality over multiple WAN links

Authentication Programming

• Router(config)#username Romeo password Juliet

• Router(config-if)#encapsulation ppp• Router(config-if)#ppp authentication pap• Router(config-if)#ppp pap sent-username GIN

password RUMMY– Name and password are case sensitive

• Dialer-map command tells each router what to do (suggest it be used) – see 3.2.2

Configuring CHAP

• Router(config-if)#encapsulation ppp• Router(config-if)#ppp authentication chap • Router(config-if)#ppp chap hostname GIN• Router(config-if)#ppp chap password RUMMY

– Remember that you will also have to configure a local username/password database, or point the router to the TACACS+ or RADIUS server that has that information.

– Router(config-if)#ppp authentication pap chap

Callback

• provides a client/server relationshipbetween the endpoints of a point-to-point connection

• can be used to control access and toll costs between hosts

• the calling router (the callback client) pases authentication information to the remote router (the callback server)

• for PPP callback server disconnects, and then places a return call

• Both routers on a point-to-point link must be configured for PPP callback – server/client

Configuration for Callback

• Server(config)#username Client password itsasecret • Server(config)#map-class dialer DIALBACK • Server(config-map-class)#dialer callback-server

username• Server(config-map-class)#exit • Server(config)#interface async 1• Server(config-if)#ppp callback accept• Server(config-if)#dialer map ip 10.1.1.2 name Client

class DIALBACK modem-script hayes56k broadcast 5556002

Client Configuration

• Client(config)#interface async 1• Client(config-if)#encapsulation ppp• Client(config-if)#ppp authentication chap• Client(config-if)#ppp callback request• Client(config-if)#dialer in-band• Client(config-if)#dialer-group 1• Client(config-if)#dialer map ip 10.1.1.1 name

Server modem-script hayes56k broadcast 5556001

Compression• CPU or Memory Intensive

– Can impact router performance

• Use only on slow lines

• Use commands to show impact– Show process cpu– Show processes memory

PPP Multilink

• Use MLP with applications in which bandwidth requirements are dynamic, such as remote LAN access applications for telecommuters or small office, home office (SOHO) environments

• Creates bundles

• RFC 1717 and 1990

MMP Features

• Combine multiple physical links into one logical link (bundle)

• Receive and reassemble upper-layer protocol data units (PDUs)

• Receive PDUs of a negotiated size

Troubleshooting Commands

• Show dialer– view the status of asynchronous dialup connections.

• Debug PPP negotiation– troubleshooting the PPP LCP activities such as

authentication, compression, and MLP

• Debug PPP Authentication– output is limited to CHAP and PAP authentication

– events.