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The PPP-over-ATM feature enables a high-capacity central site router with an Asynchronous Transfer Mode (ATM) interface to terminate multiple remote Point-to-Point Protocol (PPP) connections. These PPP connections are typically received from remote branch offices that have PPP-compatible devices interconnecting directly to Cisco StrataCom's ATM Switch Interface Shelf (AXIS) equipment through a leased-line connection.
A logical interface, known as a virtual access interface, associates each PPP connection to an ATM permanent virtual circuit (PVC). You can create this logical interface using the atm pvc command. This configuration allows the PPP protocol to terminate at the router ATM interface as if received from a typical PPP serial interface. Each PPP connection is encapsulated in a separate ATM PVC, which acts as the physical medium over which PPP frames are transported.
The virtual access interface for each PVC obtains its configuration from a virtual interface template (virtual template) when the PVC is created. All PPP parameters are managed within the virtual template configuration. Multiple virtual access interfaces can spawn from a single virtual template; hence, multiple PVCs can use a single virtual template.
Prior to configuring the ATM PVC, you typically configure the virtual template, which is configured identically as a serial interface. Configuration changes made to the virtual template are automatically propagated to the individual virtual access interfaces. (See the "Restrictions" section).
Once the router is configured for PPP over 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.
The virtual access interface remains associated with a PVC as long as the PVC is configured. Once the PVC is deconfigured, the virtual access interface is marked as deleted. Shutting down the associated ATM interface also causes the virtual access interface to be marked as down (within 10 seconds), bringing the PPP connection down. If a keepalive timer of the virtual template is set on the interface, the virtual access interface uses the PPP echo mechanism to verify the existence of the remote peer. If an interface failure is detected and the PPP connection is brought down, the virtual access interface remains up.
The PPP-over-ATM feature is ideally suited for enterprise customers or customers who use Cisco StrataCom ATM switches to access wide-area networks (WANs) or public ATM networks, such as organizations with many remote branch offices requiring access to high-density corporate headquarters. Figure 18 shows a typical scenario for using PPP over ATM.
Dedicated lower-speed connections can be aggregated across a wide area and concentrated into high-capacity ATM core routers. This solution realizes the following benefits:
Cisco IOS software supports up to 300 interfaces per router. PPP over ATM requires two interfaces per PVC connection: one for the point-to-point subinterface and one for the virtual access interface. In addition, each virtual template configuration requires an interface. Thus, the maximum number of aal5ppp-type PVCs that can be configured is something less than 150. The exact number that can be supported is dependent on the configuration of the router and the number of all other types of interfaces supported on the router.
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. (For further information on configuring an AAA server, see the "Per-User Configuration" feature chapter in this document.)
If the parameters of the virtual template are not explicitly defined before configuring the ATM PVC, 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, it is recommended 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 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) queuing is supported when applied to PPP-over-ATM virtual access interfaces. Other types of queuing which are typically configured on the main interface are not (for example, fair-queuing). If configured, these configuration lines are ignored when applied to a PPP-over-ATM interface.
While fast switching is supported, flow and optimum switching are not; these configurations are ignored on the PPP-over-ATM virtual access interface. Fast switching is enabled by default for the virtual template configuration. If fast switching is not desired, use the no ip route-cache command to disable it.
The PPP reliable link that uses Link Access Procedure, Balanced (LAPB) is not supported.
Because an ATM PVC is configured for this feature, the following standard PPP features are not applicable and should not be configured:
This feature is supported on these platforms:
To use this feature, the central site router must be equipped with Cisco IOS Release 11.2(4)F or later software and configured for PPP over ATM. In addition, remote branch offices must have PPP configured on PPP-compatible devices interconnecting directly to StrataCom AXIS equipment through a leased-line connection. The AXIS shelves provide frame forwarding encapsulation and are terminated on BPX cores prior to connection to the central site router.
To enable PPP over ATM, complete the following tasks. The first task is optional but recommended. The remaining tasks are required.
Prior to configuring the ATM PVC for PPP over ATM, you typically create and configure a virtual template. To create and configure a virtual template, complete the following tasks beginning in global configuration mode:
Other optional configuration commands can be added to the virtual template configuration. For example, you can enable the PPP authentication on the virtual template using the ppp authentication chap command. Refer to the "Virtual Interface Template Service" feature chapter in this document for additional information.
After you create a virtual template for PPP over ATM, you must specify a point-to-point subinterface per PVC connection. To specify an ATM point-to-point subinterface, complete the following task in interface configuration mode:
| Task | Command |
|---|---|
| Specify an ATM point-to-point subinterface. | interface atm slot/port.subinterface-number point-to-point |
After you create a virtual template and point-to-point subinterfaces for PPP over ATM, you must create a PPP-over-ATM PVC. To create a PPP-over-ATM PVC, perform the following task in subinterface configuration mode:
| Task | Command |
|---|---|
| Create a PPP-over-ATM PVC. | atm pvc vcd vpi vci aal5ppp [peak average [burst]] [oam [seconds]] virtual-template number |
The peak rate value is typically identical to the average rate or some suitable multiple thereof (up to 64 times for the Cisco 7500 and unlimited for the Cisco 4500 and Cisco 4700 routers).
The average rate value should be set to the line rate available at the remote site, because the remote line rate will 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, PPP over ATM is not typically an end-to-end ATM connection, and therefore enabling OAM is not recommended.
The following example configures PPP over ATM to use PPP unnumbered link and Challenge Handshake Authentication Protocol (CHAP) authentication:
console#configure terminal! Configure a Virtual Template and Create a Virtual Template Interface: console#interface virtual-template 2console(config-if)#encapsulation pppconsole(config-if)#ip unnumbered ethernet 0/0console(config-if)#ppp authentication chap! Specify an ATM Point-to-Point Interface: console(config-if)#interface atm 2/0.2 point-to-point! Enable PPP-over-ATM: console(config-subif)#atm pvc 2 0 34 aal5ppp 1536 1536 2 virtual-template 2console#end
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.2 command references.
To create a permanent virtual circuit (PVC) on the AIP or NPM interface and, optionally, to generate Operation, Administration, and Maintenance (OAM) F5 loopback cells or enable Inverse ATM ARP, use the atm pvc interface configuration command. The no form of this command removes the specified PVC.
atm pvc vcd vpi vci aal-encap [[midlow midhigh] [peak average [burst]]] [inarp [minutes]]If peak and average rate values are omitted, the PVC defaults to peak and average rates equal to the link rate. The peak and average rates are then equal. By default, the virtual circuit is configured to run as fast as possible.
The default of both the midlow and midhigh values is 0.
If the oam keyword is omitted, OAM cells are not generated. If the oam keyword is present but the seconds value is omitted, the default value of oam seconds is 10 seconds.
If the inarp keyword is omitted, Inverse ARPs are not generated. If the inarp keyword is present, but the timeout value is not given, then Inverse ARPs are generated every 15 minutes.
Interface configuration
Subinterface configuration for aal5ppp encapsulation
This command first appeared in Cisco IOS Release 10.0.
The order of command options is important. The inarp keyword can be specified either separately or before the oam keyword has been enabled. The peak, average, and burst arguments, if specified, cannot be specified after either the inarp or the oam keywords.
The Cisco IOS software dynamically creates rate queues as necessary to satisfy the requests of atm pvc commands. The software dynamically creates a rate queue when an atm pvc command specifies a peak or average rate that does not match any user-configured rate queue.
The atm pvc command creates a PVC and attaches it to the VPI and VCI specified. Both vpi and vci cannot be specified as 0; if one is 0, the other cannot be 0. The aal-encap argument determines the ATM adaptation layer (AAL) mode and the encapsulation method used. The peak and average arguments determine the rate queue used.
Use one of the aal5mux encapsulation options to dedicate the specified virtual circuit to a single protocol; use the aal5snap encapsulation option to multiplex two or more protocols over the same virtual circuit. Whether you select aal5mux or aal5snap encapsulation might depend on practical considerations, such as the type of network and the pricing offered by the network. If the network's pricing depends on the number of virtual circuits set up, aal5snap might be the appropriate choice. If pricing depends on the number of bytes transmitted, aal5mux might be the appropriate choice because it has slightly less overhead.
If you choose to specify peak or average values, you must specify both. If you set the peak and average values for aal34smds encapsulation, you must also specify the midlow and midhigh values.
Message identifier (MID) numbers, which are available only with aal34smds encapsulation, are used by receiving devices to reassemble cells from multiple packets. You can assign different midlow to midhigh ranges to different PVCs to ensure that the message identifiers are unique at the receiving end and therefore can be reassembled correctly.
When configuring an SVC, use the atm pvc command to configure the PVC that handles the SVC call setup and termination. In this case, specify the qsaal encapsulation for the aal-encap keyword. See the third example that follows.
The router generates and echoes OAM F5 loopback cells, which verify connectivity. Once OAM cell generation is enabled, a cell is transmitted periodically. The remote end must respond by echoing back the cells.
The router does not generate alarm indication signal (AIS) cells, which are used for alarm surveillance functions. However, if it receives an AIS cell, it responds by sending an OAM far-end remote failure (FERF) cell.
When configuring PPP over ATM, specify the aal5ppp encapsulation for the aal-encap keyword and specify the virtual template using the virtual-template argument. It is possible to implicitly create a virtual template when configuring PPP over ATM. In other words, if the parameters of the virtual template are not explicitly defined before configuring the ATM PVC, the PPP interface will be brought up using default values from the virtual template identified. However, some parameters (such as an IP address) take effect only if they are specified before the PPP interface comes up. Therefore, it is recommended 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, causing the newly configured parameters (such as an IP address) to take effect.
For PPP over ATM, the average rate value should be set to the line rate available at the remote site, because the remote line rate will 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 peak rate value is typically identical to the average rate or some suitable multiple thereof (up to 64 times for the Cisco 7500 and unlimited for the Cisco 4500 and Cisco 4700 routers). The burst size value 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.
The following example creates a PVC with VPI 0 and VCI 6. The PVC uses AAL AAL5-MUX with IP protocol.
atm pvc 1 0 6 aal5mux ip
The following example creates a PVC with VPI 0 and VCI 6. The PVC uses AAL AAL3/4-SMDS protocol.
atm pvc 1 0 6 aal34smds 0 15 150000 70000 10
The following example creates a PVC to be used for ATM signaling for an SVC. It specifies VPI 0 and VCI 5.
atm pvc 1 0 5 qsaal
Assuming that no static rate queue has been defined, the following example creates the PVC and also creates a dynamic rate queue with the peak rate set to the maximum allowed by the physical layer interface module (PLIM) and the average set to equal the peak rate:
atm pvc 1 1 1 aal5snap
Assuming that no static rate queue has been defined, the following example creates the PVC and also creates a dynamic rate queue with the peak rate set to 100 Mbps (100,000 kbps), the average rate set to 50 Mbps (50,000 kbps), and a burst size of 64 cells (2 * 32 cells):
atm pvc 1 1 1 aal5snap 100000 50000 2
The following example creates a PVC to be used for PPP over ATM. It specifies VPI 0 and VCI 32. The PVC uses AAL AAL5PPP and specifies a virtual template. If the remote site is using a T1 link, the peak and average rates are typically set equal to each other at 1.536 Mbps (1536 kbps) and a burst size of 64 cells is chosen (2 * 32 cells):
atm pvc 1 0 32 aal5ppp 1536 1536 2 virtual-template 2
atm aal aal3/4
atm maxvc
atm multicast
atm rate-queue
atm smds
mtu
To display all active ATM virtual circuits (PVCs and SVCs) and traffic information, use the show atm vc privileged EXEC command.
show atm vc [vcd]| vcd | (Optional) Specifies which virtual circuit about which to display information. |
Privileged EXEC
This command first appeared in Cisco IOS Release 10.0.
If no vcd value is specified, the command displays information for all PVCs and SVCs. The output is in summary form (one line per virtual circuit).
The following is sample output from the show atm vc command when no vcd value is specified, displaying statistics for all virtual circuits:
Router# show atm vc
Intfc. VCD VPI VCI Type AAL/Encaps Peak Avg. Burst
ATM4/0.1 1 1 1 PVC AAL3/4-SMDS 0 0 0
ATM4/0 2 2 2 PVC AAL5-SNAP 0 0 0
ATM4/0 3 3 3 PVC AAL5-SNAP 0 0 0
ATM4/0 4 4 4 PVC AAL5-MUX 0 0 0
ATM4/0 6 6 6 PVC AAL5-SNAP 0 0 0
ATM4/0 7 7 7 PVC AAL5-SNAP 0 0 0
The following is sample output from the show atm vc command when a vcd value is specified, displaying statistics for that virtual circuit only:
Router# show atm vc 8
ATM4/0: VCD: 8, VPI: 8, VCI: 8, etype:0x0, AAL5 - LLC/SNAP, Flags: 0x30
PeakRate: 0, Average Rate: 0, Burst: 0 *32cells, VCmode: 0xE000
InPkts: 181061, OutPkts: 570499, InBytes: 757314267, OutBytes: 2137187609
InPRoc: 181011, OutPRoc: 10, Broadcasts: 570459
InFast: 39, OutFast: 36, InAS: 11, OutAS: 6
The following is sample output from the show atm vc command when a vcd value is specified, AAL3/4 is enabled, an ATM SMDS subinterface has been defined, and a range of message identifier numbers (MIDs) has been assigned to the PVC:
Router# show atm vc 1
ATM4/0.1: VCD: 1, VPI: 0, VCI: 1, etype:0x1, AAL3/4 - SMDS, Flags: 0x35
PeakRate: 0, Average Rate: 0, Burst: 0 *32cells, VCmode: 0xE200
MID start: 1, MID end: 16
InPkts: 0, OutPkts: 0, InBytes: 0, OutBytes: 0
InPRoc: 0, OutPRoc: 0, Broadcasts: 0
InFast: 0, OutFast: 0, InAS: 0, OutAS: 0
The following is sample output from the show atm vc command when generation of OAM F5 loopback cells has been enabled:
Router# show atm vc 7
ATM4/0: VCD: 7, VPI: 7, VCI: 7, etype:0x0, AAL5 - LLC/SNAP, Flags: 0x30
PeakRate: 0, Average Rate: 0, Burst: 0 *32cells, VCmode: 0xE000
OAM frequency: 10, InARP DISABLED
InPkts: 0, OutPkts: 0, InBytes: 0, OutBytes: 0
InPRoc: 0, OutPRoc:0, Broadcast:0
InFast:0, OutFast:0, InAS:0, OutAS:0
OAM F5 cells sent: 1, OAM cells received: 0
The following is sample output from the show atm vc command for an incoming multipoint virtual circuit:
Router# show atm vc 3
ATM2/0: VCD: 3, VPI: 0, VCI: 33, etype:0x809B, AAL5 - MUX, Flags: 0x53
PeakRate: 0, Average Rate: 0, Burst: 0, VCmode: 0xE000
OAM DISABLED, InARP DISABLED
InPkts: 6646, OutPkts: 0, InBytes: 153078, OutBytes: 0
InPRoc: 6646, OutPRoc: 0, Broadcasts: 0
InFast: 0, OutFast: 0, InAS: 0, OutAS: 0
interface = ATM2/0, call remotely initiated, call reference = 18082
vcnum = 3, vpi = 0, vci = 33, state = Active
aal5mux vc, multipoint call
Retry count: Current = 0, Max = 10
timer currently inactive, timer value = never
Root Atm Nsap address: DE.CDEF.01.234567.890A.BCDE.F012.3456.7890.1234.12
The following is sample output from the show atm vc command for an outgoing multipoint virtual circuit:
Router# show atm vc 6
ATM2/0: VCD: 6, VPI: 0, VCI: 35, etype:0x800, AAL5 - MUX, Flags: 0x53
PeakRate: 0, Average Rate: 0, Burst: 0, VCmode: 0xE000
OAM DISABLED, InARP DISABLED
InPkts: 0, OutPkts: 818, InBytes: 0, OutBytes: 37628
InPRoc: 0, OutPRoc: 0, Broadcasts: 818
InFast: 0, OutFast: 0, InAS: 0, OutAS: 0
interface = ATM2/0, call locally initiated, call reference = 3
vcnum = 6, vpi = 0, vci = 35, state = Active
aal5mux vc, multipoint call
Retry count: Current = 0, Max = 10
timer currently inactive, timer value = never
Leaf Atm Nsap address: DE.CDEF.01.234567.890A.BCDE.F012.3456.7890.1234.12
Leaf Atm Nsap address: CD.CDEF.01.234567.890A.BCDE.F012.3456.7890.1234.12
The following is sample output from the show atm vc command for a PPP-over-ATM connection:
Router# show atm vc 1 ATM8/0.1: VCD: 1, VPI: 41, VCI: 41, etype:0x8, AAL5 - PPP, Flags: 0xC38 PeakRate: 155000, Average Rate: 155000, Burst: 96, VCmode: 0xE000 virtual-access: 1, virtual-template: 1 OAM DISABLED, InARP DISABLED InPkts: 13, OutPkts: 10, InBytes: 198, OutBytes: 156 InPRoc: 13, OutPRoc: 10, Broadcasts: 0 InFast: 0, OutFast: 0, InAS: 0, OutAS: 0 OAM F5 cells sent: 0, OAM cells received: 0
Table 18 describes the fields shown in the displays.
| Field | Description |
|---|---|
| interface | Interface slot and port. |
| VCD | Virtual circuit descriptor (virtual circuit number). |
| VPI | Virtual path identifier. |
| VCI | Virtual channel identifier. |
| Type | Type of virtual circuit, either PVC or SVC. |
| etype | Ethernet type. |
| AAL/Encaps | Type of ATM adaptation layer (AAL) and encapsulation. |
| Flags | Bit mask describing virtual circuit information. The flag values are summed to result in the displayed value.
0x40--SVC 0x20--PVC 0x10--ACTIVE 0x0--AAL5-SNAP 0x2--AAL5-FRNLPID 0x3--AAL5-MUX 0x4--AAL3/4-SMDS 0x5--QSAAL 0x6--ILMI 0x7--AAL5-LANE 0x8--AAL5-PPP |
| PeakRate | Kilobits per second transmitted at the peak rate. |
| Average Rate | Kilobits per second transmitted at the average rate. |
| Burst | Value that, when multiplied by 32, equals the maximum number of ATM cells the virtual circuit can transmit at peak rate. |
| VCmode | AIP-specific or NPM-specific register describing the usage of the virtual circuit. This register contains values such as rate queue, peak rate, and AAL mode, which are also displayed in other fields. |
| virtual-access | Virtual access interface identifier. |
| virtual-template | Virtual template identifier. |
| InPkts | Total number of packets received on this virtual circuit. This number includes all silicon-switched, fast-switched, autonomous-switched, and process-switched packets. |
| OutPkts | Total number of packets sent on this virtual circuit. This number includes all silicon-switched, fast-switched, autonomous-switched, and process-switched packets. |
| InBytes | Total number of bytes received on this virtual circuit. This number includes all silicon-switched, fast-switched, autonomous-switched, and process-switched bytes. |
| OutBytes | Total number of bytes sent on this virtual circuit. This number includes all silicon-switched, fast-switched, autonomous-switched, and process-switched bytes. |
| InPRoc | Number of process-switched input packets. |
| OutPRoc | Number of process-switched output packets. |
| Broadcast | Number of process-switched broadcast packets. |
| InFast | Number of fast-switched input packets. |
| OutFast | Number of fast-switched output packets. |
| InAS | Number of autonomous-switched or silicon-switched input packets. |
| OutAS | Number of autonomous-switched or silicon-switched output packets. |
| OAM frequency: 10 | OAM cells are sent every 10 seconds. |
| OAM F5 cells sent: 1 | Number of OAM cells sent on this virtual circuit. |
| OAM cells received: 0 | Number of OAM cells received on this virtual circuit. |
atm pvc
For more information on configuring the AXIS Shelf for frame forwarding encapsulation, refer to the AXIS 4 Command Supplement for command line instructions or the StrataView Plus Operations Guide for StrataView Plus instructions. If you configure the AXIS using the command line interface, use the addport and addchan commands and select frame forwarding for the port_type and chan_type arguments, respectively.
For more information on configuring the AAA server, refer to the "Per-User Configuration" feature chapter in this document.
For more information on configuring virtual templates, refer to the "Virtual Interfaces Template Service" feature chapter in this document.
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