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Cisco IOS XE Broadband Access Aggregation and DSL Configuration Guide, Release 2
- Part 1: Broadband Access Aggregation Overview
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Part 2: PPPoE
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Providing Protocol Support for Broadband Access Aggregation of PPPoE Sessions
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PPPoE Session Limit Local Override
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PPPoE Circuit-Id Tag Processing
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Providing Session Limit Support
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PPP-Max-Payload and IWF PPPoE Tag Support
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PPPoE - QinQ Support
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PPPoE Session Limiting on Inner QinQ VLAN
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PPPoE Agent Remote-ID and DSL Line Characteristics Enhancement
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Enabling PPPoE Relay Discovery and Service Selection Functionality
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Configuring Cisco Subscriber Service Switch Policies
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Per Session Queuing and Shaping for PPPoEoVLAN Using RADIUS
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802.1P CoS Bit Set for PPP and PPPoE Control Frames
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PPPoE Smart Server Selection
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Monitoring PPPoE Sessions with SNMP
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PPPoE on ATM
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PPPoE on Ethernet
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- Part 3: High Availability
Table Of Contents
Prerequisites for PPPoE on ATM
Information About PPPoE on ATM
Creating and Configuring a Virtual Template
Specifying an ATM Subinterface
Configuration Examples for PPPoE on ATM
Feature Information for PPPoE on ATM
PPPoE on ATM
First Published: March 27, 2000Last Updated: November 25, 2009This feature module describes the PPP over Ethernet (PPPoE) on ATM feature. The PPPoE on ATM feature provides the ability to connect a network of hosts over a simple bridging-access device to a remote access concentrator.
Finding Feature Information
For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for PPPoE on ATM" section
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
This document includes the following sections:
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Prerequisites for PPPoE on ATM
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Prerequisites for PPPoE on ATM
Before you can configure PPPoE on ATM, you need to specify a virtual template for the PPPoE sessions using the virtual-template command.
Restrictions for PPPoE on ATM
The following restrictions apply when PPPoE on ATM is used:
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For more information, refer to the PPPoEoA over ATM AAL5Mux feature: http://www.cisco.com/en/US/docs/ios/bbdsl/configuration/guide/bba_pppoeoa_aal5mux.html•
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Information About PPPoE on ATM
The PPPoE on ATM feature provides the ability to connect a network of hosts over a simple bridging-access device to a remote access concentrator. With this model, each host utilizes its own PPPoE stack and the user is presented with a familiar user interface. Access control, billing and type of service can be done on a per-user, rather than a per-site, basis. Before a point-to-point connection over Ethernet can be provided, each PPP session must learn the Ethernet address of the remote peer and establish a unique session identifier. A unique session identifier is provided by the PPPoE Discovery Stage protocol.
Figure 1 shows a sample network topology using PPPoE on ATM.
Figure 1 PPPoE on ATM Sample Network Topology
PPPoE Stage Protocols
PPPoE has two distinct stage protocols. The stage protocols are listed and summarized in Table 1.
There are four steps to the Discovery Stage:
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When a host wishes to initiate a PPPoE session, it must first perform discovery to identify the Ethernet MAC address of the peer and establish a PPPOE SESSION_ID. Although PPP defines a peer-to-peer relationship, discovery is inherently a client/server relationship. In the discovery process, a host (the client) discovers an access concentrator (the server). Based on the network topology, there may be more than one access concentrator that the host can communicate with. The Discovery Stage allows the host to discover all access concentrators and then select one. When discovery is completed, both the host and the selected access concentrator have the information they will use to build their point-to-point connection over Ethernet.
Benefits of PPPoE on ATM
The PPPoE on ATM feature provides service-provider digital subscriber line (DSL) support. As service providers begin DSL deployments, two of their most significant goals are to ease and facilitate consumer end adoption and to preserve as much of the dialup model as possible. PPPoE serves to advance both of these goals by leveraging ethernet scale curves and embedded base (such as ATM NICs) and by preserving the point-to-point session used by internet service providers (ISPs) in today's dialup model.
Using a PPPoE client (available from RouterWare), a PPP session can be initiated on an Ethernet connected client through a standard ADSL modem. The session is transported over the ATM DSL link via RFC 1483 Ethernet bridged frames and can terminate either in the LAN emulation client (LEC) central office or the ISP point of presence (POP). The termination device can be an aggregation box such as the Cisco 6400 or a router such as the Cisco 7200 series platforms.
As customers deploy asymmetric DSL (ADSL), they will encounter the need to enable users to access remote-access concentrators via simple bridges connecting Ethernet and ATM networks.
How to Configure PPPoE on ATM
See the following sections for configuration tasks for the PPPoE on ATM feature. Each task in the list indicates if the task is optional or required.
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Enabling PPP over ATM
After you configure the Cisco router or access server for Ethernet encapsulation, you must configure the physical interface with the PVC and apply a virtual template with PPP encapsulation to the PVC that it applies to. To configure the physical interface that will carry the PPPoE session and link it to the appropriate virtual template interface, use the following commands:
SUMMARY STEPS
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encapsulation aal5snap13.
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DETAILED STEPS
Creating and Configuring a Virtual Template
Prior to configuring the ATM PVC for PPPoE on ATM, you typically create and configure a virtual template. To create and configure a virtual template, use the following commands:
SUMMARY STEPS
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DETAILED STEPS
Other optional configuration commands can be added to the virtual template configuration. All PPP parameters are managed within the virtual template configuration. Configuration changes made to the virtual template are automatically propagated to the individual virtual access interfaces. Multiple virtual access interfaces can spawn from a single virtual template; hence, multiple PVCs can use a single virtual template.
Cisco IOS software supports up to 25 virtual template configurations. If greater numbers of tailored configurations are required, an authentication, authorization, and accounting (AAA) server may be employed.
If the parameters of the virtual template are not explicitly defined before the ATM PVC is configured, the PPP interface is brought up using default values from the virtual template identified. Some parameters (such as an IP address) take effect only if specified before the PPP interface comes up. Therefore, Cisco recommends that you explicitly create and configure the virtual template before configuring the ATM PVC to ensure such parameters take effect. Alternatively, if parameters are specified after the ATM PVC has already been configured, you should issue a shutdown command followed by a no shutdown command on the ATM subinterface to restart the interface; this restart will cause the newly configured parameters (such as an IP address) to take effect.
Network addresses for the PPP-over-ATM connections are not configured on the main ATM interface or subinterface. Instead, these connections are configured on the appropriate virtual template or obtained via AAA.
The virtual templates support all standard PPP configuration commands; however, not all configurations are supported by the PPP-over-ATM virtual access interfaces. These restrictions are enforced at the time the virtual template configuration is applied (cloned) to the virtual access interface. These restrictions are described in the following paragraphs.
Only standard first-in, first-out (FIFO) queueing is supported when applied to PPP-over-ATM virtual access interfaces. Other types of queueing that are typically configured on the main interface are not (for example, fair queueing). If configured, these configuration lines are ignored when applied to a PPP-over-ATM interface.
Although Cisco Express Forwarding (CEF) switching is supported, fast switching, flow, and optimum switching are not; these configurations are ignored on the PPP-over-ATM virtual access interface. CEF is enabled by default for IP. All other protocol traffic will be processed switched.
Note
Because an ATM PVC is configured for this feature, the following standard PPP features are not applicable and should not be configured:
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Specifying an ATM Subinterface
After you create a virtual template for PPPoE on ATM, specify a multipoint or point-to-point subinterface per PVC connection. To specify an ATM multipoint subinterface, use the following commands:
SUMMARY STEPS
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DETAILED STEPS
Creating an ATM PVC
After you create a virtual template and specify an ATM subinterface, you must create an ATM PVC. To create an ATM PVC, use the following commands:
SUMMARY STEPS
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DETAILED STEPS
The peak rate value is typically identical to the average rate or some suitable multiple thereof.
The average rate value should be set to the line rate available at the remote site, because the remote line rate will typically have the lowest speed of the connection.
For example, if the remote site has a T1 link, set the line rate to 1.536 Mbps. Because the average rate calculation on the ATM PVC includes the cell headers, a line rate value plus 10 or 15 percent may result in better remote line utilization.
The burst size depends on the number of cells that can be buffered by receiving ATM switches and is coordinated with the ATM network connection provider. If this value is not specified, the default, which is the equivalent to one maximum length frame on the interface, is used.
Operations, Administration and Maintenance (OAM) F5 cell loopback is provided by the remote AXIS shelf so OAM may be enabled. However, PPPoE on ATM is not typically an end-to-end ATM connection, and therefore enabling OAM is not recommended.
Once you configure the router for PPPoE on ATM, the PPP subsystem starts and the router attempts to send a PPP configure request to the remote peer. If the peer does not respond, the router periodically goes into a "listen" state and waits for a configuration request from the peer. After a timeout (typically 45 seconds), the router again attempts to reach the remote router by sending configuration requests.
Enabling PPPoE on an ATM PVC
To enable PPPoE on an ATM PVC, use the following commands:
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for PPPoE on ATM
This section provides the following configuration example:
PPPoE on ATM : Example
The following example configures PPPoE on ATM to accept dial-in PPPoE sessions. The virtual access interface for the PPP session is cloned form virtual template interface 1. On subinterface ATM 2/0.1, ATM PVC with VPI 0 and VCI 60 is configured with Logical Link Control (LLC)/Subnetwork Access Protocol (SNAP) encapsulation and is configured to run PPPoE.
bba-group pppoe pppoe-groupvirtual-template 1sessions per-vc limit 1 sessions per-mac limit 4000interface atm 2/0.1 multipointip address 192.0.10.2 255.255.255.0 secondaryrange pvc 1/100 1/202pvc 0/60dbs enableencapsulation aal5snapprotocol pppoe group twocreate on-demandinterface virtual-template 1ip addr 10.0.1.2 255.255.255.0mtu 1492Where to Go Next
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Additional References
The following sections provide references related to the PPPoE on ATM feature.
Related Documents
Cisco IOS commands
Broadband and DSL commands
Cisco IOS Broadband Access Aggregation and DSL Command Reference
Enabling PPP authentication on the virtual template
Configuring an AAA server
Configuring Broadband and DSL
Cisco IOS XE Broadband Access Aggregation and DSL Configuration Guide
Standards
MIBs
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
RFC 1483
Multiprotocol Encapsulation over ATM Adaptation Layer 5
RFC 2364
PPP over AAL5
RFC 2516
A Method for Transmitting PPP over Ethernet (PPPoE)
Technical Assistance
Feature Information for PPPoE on ATM
Table 2 lists the features in this module and provides links to specific configuration information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note
Glossary
AAL5—ATM Adaptation Layer 5
ADSL—Asymmetric Digital Subscriber Line
ATM—Asynchronous Transfer Mode
CPCS—Common Part of Convergence Sublayer
CPI—Common Part Indicator
CRC—Cyclic Redundancy Check
DSLAM—Digital Subscriber Line Access Multiplexer
FCS—Frame Check Sequence
IETF—Internet Engineering Task Force
ID-Identifier
IP—Internet Protocol
L2TP—Layer two Tunneling Protocol
LAN—Local Area Network
LLC—Logical Link Control
MAC—Media Access Control
PDU—Protocol Data Unit
PPP—Point to Point Protocol
PPPoE—Point to Point Protocol over Ethernet
PVC—Permanent Virtual Connection
VPDN—Virtual Private Dialup Network
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