Chapter 3 -- PPP
PPP – A continuation of CCNA –
Semester 4
DataLink (Layer 2) TCP/IP
Protocols
• SLIP - SLIP is a standard protocol for pointto-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.