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PPP over Frame Relay DTE Example
PPP over Frame Relay DCE Example
PPP over Frame Relay
Feature Summary
The PPP over Frame Relay feature allows a router to establish end-to-end Point-to-Point Protocol (PPP) sessions over Frame Relay. IP datagrams are transported over the PPP link using RFC 1973 compliant Frame Relay framing. This feature is useful for remote users running PPP to access their Frame Relay corporate networks as shown in . shows a connectivity scenario using the Cisco 90i D4 channel card, which is capable of supporting Integrated Services Digital Network (ISDN) Digital Service Loop (DSL), PPP, or Frame Relay, which connects to an Internet Service Provider (ISP) or corporate network.
Figure 1
PPP Over Frame Relay Scenario
Figure 2 PPP over Frame Relay Using the Cisco 90i D4 Channel Unit
Benefits
PPP over Frame Relay provides the following benefits:
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Allows end-to-end PPP sessions over Frame Relay.
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List of Terms
data-link connection identifier (DLCI)— A value that specifies a PVC or SVC in a Frame Relay network. In the basic Frame Relay specification, DLCIs are locally significant (connected devices might use different values to specify the same connection). In the LMI extended specification, DLCIs are globally significant (DLCIs specify individual end devices).
Integrated Services Digital Network (ISDN)—Communication protocols offered by telephone companies that permit telephone networks to carry data, voice, and other source traffic.
Link Control Protocol (LCP)—A protocol that establishes, configures, and tests data link connections used by PPP.
permanent virtual circuit (PVC)—Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and tear down in situations where certain virtual circuits must exist all the time.
Point-to-Point Protocol (PPP)—A protocol that encapsulates network layer protocol information over point-to-point links. The RFC for PPP is RFC 1661.
virtual circuit (VC)—A logical circuit created to ensure reliable communication between two network devices. A virtual circuit can be either permanent (a PVC) or switched (an SVC). Virtual circuits are used in Frame Relay and X.25.
Restrictions
The following restrictions apply when using PPP over Frame Relay:
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Platforms
This feature is supported on these platforms:
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Prerequisites
Before you can configure PPP over Frame Relay, Frame Relay must be enabled on the router using the encapsulation frame-relay command.
Supported MIBs and RFCs
This feature supports the RFC 1973.
No new MIBs are supported by this feature.
Functional Description
PPP over Frame Relay is compliant to the functionality and encapsulation specifications as outlined in RFC 1973. The frame format is shown in .
A PPP connection is established over the Frame Relay permanent virtual circuit (PVC). The PPP session does not occur unless the associated Frame Relay PVC is in an "active" state. The Frame Relay VC can coexist with other circuits using different Frame Relay encapsulation methods, such as RFC 1490 and Cisco proprietary, over the same Frame Relay link. There can be multiple PPP-in-Frame Relay circuits existing on one Frame Relay link.
One PPP connection resides on one virtual access interface, which is internally created from a virtual template interface. A virtual access interface is cloned from a virtual template interface. The virtual access interfaces is coexistent with the creation of the Frame Relay circuit when the corresponding DLCI is configured. One virtual template interface, containing all the necessary PPP and network protocol information is shared by multiple virtual access interfaces. Hardware compression and fancy queuing algorithms, such as weighted fair queuing, custom queuing, and priority queuing, are not applied to virtual access interfaces. Once a Frame Relay circuit is established using PPP over Frame Relay, all incoming and outgoing packets on this circuit are under RFC 1973 PPP-in-Frame-Relay encapsulation compliance until this DLCI is removed from the configuration. Refer to the Cisco IOS Release 11.3 Wide Area Configuration Guide and Command Reference documents for information about Frame Relay configuration options.
Figure 3 PPP over Frame Relay Frame Format
The breakdown of the Frame Relay frame format components is listed in .
Configuration Task
The only task required to implement PPP over Frame Relay is to configure the interface with the locally terminated PVC and the associated virtual template for PPP and IP, as described in the following section.
Enable PPP over Frame Relay
After you configure the Cisco router or access server for Frame Relay encapsulation, you must configure the physical interface with the PVC and apply a virtual template with PPP encapsulation to the DLCI that it applies to. To configure the physical interface that will carry the PPP session and link it to the appropriate virtual template interface, perform the following task in interface configuration mode:
Define the PVC and map it to the virtual template.
frame-relay interface-dlci dlci [ppp virtual-template-name-string]
Configuration Examples
This section provides the following examples:
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PPP over Frame Relay DTE Example
The following example configures a router as a data terminating equipment (DTE) device for PPP over Frame Relay. Subinterface 2.1 contains the necessary DLCI and virtual template information. The virtual template interface (interface virtual-template 1) contains the PPP information that is applied to the PPP session associated with DLCI 32 on serial subinterface 2.1. Refer to the Cisco IOS Release 11.3 Wide-Area Configuration Guide and Wide-Area Networking Command Reference for information about Frame Relay configuration options.
interface serial 2no ip addressencapsulation frame-relayframe-relay lmi-type ansi!interface serial 2.1 point-to-pointframe-relay interface-dlci 32 ppp virtual-template1!interface Virtual-Template1ip unnumbered ethernet 0ppp authentication chap pap
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PPP over Frame Relay DCE Example
The following example configures a router to act as a data communications equipment (DCE) device. Typically, a router is configured for a DCE if connecting directly to another router or if connected to a 90i D4 channel unit, which is connected to a telco channel bank. The three commands required for this type of configuration are the frame-relay switching, frame-relay intf-type dce, and frame-relay route commands. In this configuration
frame-relay switching!interface Serial2/0:0no ip addressencapsulation frame-relay IETFframe-relay lmi-type ansiframe-relay intf-type dceframe-relay route 31 interface Serial1/2 100frame-relay interface-dlci 32 ppp Virtual-Template1!interface Serial2/0:0.2 point-to-pointno ip addressframe-relay interface-dlci 40 ppp Virtual-Template2!interface Virtual-Template1ip unnumbered Ethernet0/0peer default ip address pool defaultppp authentication chap pap!interface Virtual-Template2ip address 100.1.1.2 255.255.255.0ppp authentication chap pap
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Command Reference
This section documents the frame-relay interface-dlci command, which is revised to add the ppp keyword and virtual-template-name-string argument for PPP over Frame Relay. Only the revised keywords, which are used to configure PPP over Frame Relay are included. The show interfaces and show frame-relay pvc commands are modified to display configuration, status, and statistical information as related to Frame Relay interfaces configured for PPP.
frame-relay interface-dlci
To define a specific PVC to a DLCI and apply a virtual template configuration to a PPP session, use this form of the frame-relay interface-dlci interface configuration command. To remove this assignment, use the no form of this command.
frame-relay interface-dlci dlci [ppp virtual-template-name-string]
no frame-relay interface-dlci dlci [ppp virtual-template-name-string]Syntax Description
Default
PPP-in-Frame Relay encapsulation type is disabled.
Command Mode
Interface and subinterface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 10.0.
The ppp keyword and virtual-template-name-string argument first appeared in Cisco IOS Release 11.3 T.Example
The following example specifies DLCI 26 over subinterface serial 1.1 and assigns the characteristics under virtual-template 2 to this PPP connection:
interface serial1.1 point-to-pointframe-relay interface-dlci 26 ppp virtual-template2Related Commands
show frame-relay pvc
show interfaceshow frame-relay pvc
To display statistics about PVCs for Frame Relay interfaces, use the show frame-relay pvc EXEC command.
show frame-relay pvc [type number [dlci]]
Syntax Description
Command Mode
EXEC
Usage Guidelines
This command first appeared in Cisco IOS Release 10.0.
This command was modified to display statistics about virtual access interfaces used for PPP connections over Frame Relay in Cisco IOS Release 11.3 T.
Use this command to monitor the PPP link control protocol (LCP) state as being open with an "up" state, or closed with a "down" state.
Sample Display
The following is sample output from the show frame-relay pvc command that shows the PVC statistics for serial interface 5, slot 1 and DLCI 55 is up. Refer to the Cisco IOS Release 11.3 Wide-Area Configuration Guide and Wide-Area Networking Command Reference for field description information.
Router# show frame-relay pvc 55PVC Statistics for interface Serial5/1 (Frame Relay DTE)DLCI = 55, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial5/1.1input pkts 9 output pkts 16 in bytes 154out bytes 338 dropped pkts 6 in FECN pkts 0in BECN pkts 0 out FECN pkts 0 out BECN pkts 0in DE pkts 0 out DE pkts 0out bcast pkts 0 out bcast bytes 0pvc create time 00:35:11, last time pvc status changed 00:00:22Bound to Virtual-Access1 (up, cloned from Virtual-Template5)Debug Commands
The debug frame-relay ppp command is added to debug PPP sessions over Frame Relay.
debug frame-relay ppp
Use the debug frame-relay ppp EXEC command to display debugging information. To disable debugging output, use the no form of this command.
[no] debug frame-relay ppp
Usage Guidelines
Displays error messages for link states and LMI status changes for PPP over Frame Relay sessions.
To debug process-switched packets, use the debug frame-relay packet and/or debug ppp packet commands. To analyze the packets that have been sent on a Frame Relay interface, use the debug frame-relay packet command.
The debug frame-relay ppp command is generated from process level switching only and is not CPU intensive.
Sample Display
shows output from the debug frame-relay ppp command where the encapsulation failed for VC 100.
Figure 4 Sample Debug Frame-Relay PPP Output
Router# debug frame-relay pppFR-PPP: encaps failed for FR VC 100 on Serial0 downFR-PPP: input- Serial0 vc or va down, pak droppedshows the output from the debug frame relay ppp and debug frame-relay packet commands. This example shows a virtual interface (virtual interface 1) successfully establishing a PPP connection over PPP.
Figure 5 Sample Debug Frame-Relay PPP and Debug Frame Relay Packet Output
Router# debug frame-relay pppRouter# debug frame-relay packetVi1 LCP: O CONFREQ [Closed] id 1 len 10Vi1 LCP: MagicNumber 0xE0638565 (0x0506E0638565)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 16Vi1 PPP: I pkt type 0xC021, datagramsize 14Vi1 LCP: I CONFACK [REQsent] id 1 len 10Vi1 LCP: MagicNumber 0xE0638565 (0x0506E0638565)Vi1 PPP: I pkt type 0xC021, datagramsize 14Vi1 LCP: I CONFREQ [ACKrcvd] id 6 len 10Vi1 LCP: MagicNumber 0x000EAD99 (0x0506000EAD99)Vi1 LCP: O CONFACK [ACKrcvd] id 6 len 10Vi1 LCP: MagicNumber 0x000EAD99 (0x0506000EAD99)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 16Vi1 IPCP: O CONFREQ [Closed] id 1 len 10Vi1 IPCP: Address 170.100.9.10 (0x0306AA64090A)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 16Vi1 PPP: I pkt type 0x8021, datagramsize 14Vi1 IPCP: I CONFREQ [REQsent] id 1 len 10Vi1 IPCP: Address 170.100.9.20 (0x0306AA640914)Vi1 IPCP: O CONFACK [REQsent] id 1 len 10Vi1 IPCP: Address 170.100.9.20 (0x0306AA640914)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 16Vi1 PPP: I pkt type 0x8021, datagramsize 14Vi1 IPCP: I CONFACK [ACKsent] id 1 len 10Vi1 IPCP: Address 170.100.9.10 (0x0306AA64090A)Vi1 PPP: I pkt type 0xC021, datagramsize 16Vi1 LCP: I ECHOREQ [Open] id 1 len 12 magic 0x000EAD99Vi1 LCP: O ECHOREP [Open] id 1 len 12 magic 0xE0638565Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 18Vi1 LCP: O ECHOREQ [Open] id 1 len 12 magic 0xE0638565Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 18Vi1 LCP: echo_cnt 4, sent id 1, line upshows the output for the debug frame-relay ppp and debug frame-relay packet commands which report a failed PPP over Frame Relay session. The problem is due to a challenge handshake authentication protocol (CHAP) failure.
Figure 6 Failed PPP over Frame Relay Debug Output
Router# debug frame-relay pppRouter# debug frame-relay packetVi1 LCP: O CONFREQ [Listen] id 24 len 10Vi1 LCP: MagicNumber 0xE068EC78 (0x0506E068EC78)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 16Vi1 PPP: I pkt type 0xC021, datagramsize 19Vi1 LCP: I CONFREQ [REQsent] id 18 len 15Vi1 LCP: AuthProto CHAP (0x0305C22305)Vi1 LCP: MagicNumber 0x0014387E (0x05060014387E)Vi1 LCP: O CONFACK [REQsent] id 18 len 15Vi1 LCP: AuthProto CHAP (0x0305C22305)Vi1 LCP: MagicNumber 0x0014387E (0x05060014387E)Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 21Vi1 PPP: I pkt type 0xC021, datagramsize 14Vi1 LCP: I CONFACK [ACKsent] id 24 len 10Vi1 LCP: MagicNumber 0xE068EC78 (0x0506E068EC78)Vi1 PPP: I pkt type 0xC223, datagramsize 32Vi1 CHAP: I CHALLENGE id 12 len 28 from "krishna"Vi1 LCP: O TERMREQ [Open] id 25 len 4Serial2/1(o): dlci 201(0x3091), NLPID 0x3CF(PPP), datagramsize 10Vi1 PPP: I pkt type 0xC021, datagramsize 8Vi1 LCP: I TERMACK [TERMsent] id 25 len 4Serial2/1(i): dlci 201(0x3091), pkt type 0x2000, datagramsize 303%SYS-5-CONFIG_I: Configured from console by consoleVi1 LCP: TIMEout: Time 0x199580 State Listen
