Table Of Contents
Automatic Protection Switching of Packet-over-SONET Circuits
Configure APS Working and Protect Interfaces
Configure SONET Alarm Reporting
Multiple APS Interface Configuration
Automatic Protection Switching of Packet-over-SONET Circuits
Feature Summary
The automatic protection switching (APS) feature is supported on Cisco 7500 series routers. This feature allows switchover of packet-over-SONET (POS) circuits and is often required when connecting SONET equipment to telco equipment. APS refers to the mechanism of bringing a "protect" POS interface into the SONET network as the "working" POS interface on a circuit from the intervening SONET equipment.
The protection mechanism used for this feature is "1+1, Bidirectional, nonrevertive" as described in the Bellcore publication TR-TSY-000253, SONET Transport Systems; Common Generic Criteria, Section 5.3. In the 1+1 architecture, there is one working interface (circuit) and one protect interface, and the same payload from the transmitting end is sent to both the receiving ends. The receiving end decides which interface to use. The line overhead (LOH) bytes (K1 and K2) in the SONET frame indicate both status and action.
The protect interface is configured with the IP address of the router that has the working interface. The APS Protect Group Protocol, which runs on top of UDP, provides communication between the process controlling the working interface and the process controlling the protect interface. Using this protocol, POS interfaces can be switched due to a router failure, degradation or loss of channel signal, or manual intervention. In bidirectional mode, the receive and transmit channels are switched as a pair. In unidirectional mode, the transmit and receive channels are switched independently. For example, if the receive channel on the working interface has a loss of channel signal, both the receive and transmit channels are switched.
In addition to the new Cisco IOS commands added for the APS feature, the POS interface configuration commands pos threshold and pos report have been added to support user configuration of the bit error rate (BER) thresholds and reporting of SONET alarms.
Document Conventions
Command descriptions use these conventions:
•
Boldface indicates commands and keywords that are entered literally as shown.
•
•
•
•
Platforms
This feature is supported on the Cisco 7500 series platforms.
Supported MIBs and RFCs
None
Configuration Tasks
Two SONET connections are required to support APS. In a telco environment, the SONET circuits must be provisioned as APS. You must also provision the operation (for example, 1+1), mode (for example, bidirectional), and revert options (for example, no revert). If the SONET connections are homed on two separate routers (the normal configuration), an out of band (OOB) communications channel between the two routers needs to be set up for APS communication.
When configuring APS, we recommend you configure the working interface first. Normal operation with 1+1 operation is to configure it as a working interface. Also configure the IP address of the interface being used as the APS OOB communications path.
For more information on POS interfaces, refer to the Cisco IOS documentation (in particular, the "Configuring Interfaces" chapter in the Configuration Fundamentals Configuration Guide), and the installation and configuration documentation that accompanies the POS hardware.
Configure APS Working and Protect Interfaces
This section describes how to configure a working and protect interface. The tasks listed in this section are required. Configure the working interface before configuring the protect interface to avoid the protect interface from becoming the active circuit and disabling the working circuit when it is finally discovered.
To configure the working interface, perform the following steps beginning in global configuration mode:
Note
To configure the protect interface, perform the following steps beginning in global configuration mode:
Configure Other APS Options
To configure the other APS options, perform any of the following tasks in interface configuration mode. The tasks listed in this section are optional.
Monitor and Maintain APS
To provide information about system processes, the Cisco IOS software includes an extensive list of EXEC commands that begin with the word show, which, when executed, display detailed tables of system information. Following is a list of some of the common show commands for the APS feature.
Perform these tasks in privileged EXEC mode to display the information described:
Configure SONET Alarm Reporting
To configure the thresholds and the type of SONET alarms that are reported, perform any of the following tasks in interface configuration mode. The tasks listed in this section are optional. The default settings are adequate for most POS installations.
To display the current BER threshold setting or to view the reporting of the SONET alarms, use the show controllers pos EXEC command.
Configuration Examples
The following examples show how to configure basic APS on a router and how to configure more than one protect/working interface on a router by using the aps group command.
Basic APS Configuration
The following example shows the configuration of APS on router A and router B (see Figure 1). In this example, router A is configured with the working interface, and router B is configured with the protect interface. If the working interface on router A becomes unavailable, the connection will automatically switchover to the protect interface on router B.
Figure 1
Basic APS Configuration
On router A, which contains the working interface, use the following configuration:
router# configure terminalrouter(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.7 255.255.255.0router(config)# interface pos 2/0/0router(config-if)# aps working 1router(config-if)# endrouter#On router B, which contains the protect interface, use the following configuration:
router# configure terminalrouter(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.6 255.255.255.0router(config)# interface pos 3/0/0router(config-if)# aps protect 1 7.7.7.7router(config-if)# endrouter#To verify the configuration or to determine if a switchover has occurred, use the show aps command.
Multiple APS Interface Configuration
To configure more than one protect/working interface on a router, you must use the aps group command. The following example shows the configuration of grouping more than one working/protect interface on a router. In this example, router A is configured with a working interface and a protect interface, and router B is configured with a working interface and a protect interface. If the working interface 2/0/0 on router A becomes unavailable, the connection will switchover to the protect interface 3/0/0 on router B because they are both in APS group 10. Similarly, if the working interface 2/0/0 on router B becomes unavailable, the connection will switchover to the protect interface 3/0/0 on router A because they are both in APS group 20.
Figure 2
Multiple Working and Protect Interfaces Configuration
Note
On router A, which contains the working interface for group 10 and the protect interface for group 20, use the following configuration:
router# configure terminalrouter(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.6 255.255.255.0router(config)# interface pos 2/0/0router(config)# aps group 10router(config-if)# aps working 1router(config)# interface pos 3/0/0router(config-if)# aps group 20router(config-if)# aps protect 1 7.7.7.7router(config-if)# endrouter#On router B, which contains the protect interface for group 10 and the working interface for group 20, use the following configuration:
router# configure terminalrouter(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.7 255.255.255.0router(config)# interface pos 2/0/0router(config)# aps group 20router(config-if)# aps working 1router(config)# interface pos 3/0/0router(config-if)# aps group 10router(config-if)# aps protect 1 7.7.7.6router(config-if)# endrouter#To verify the configuration or to determine if a switchover has occurred, use the show aps command.
Command Reference
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 11.1 command references.
aps authenticate
To enable authentication and specify the string that must be present to accept any packet on the out of band (OOB) communications channel, use the aps authenticate interface command. To disable authentication, use the no form of the command.
aps authenticate string
no aps authenticateSyntax Description
string
Text that must be present to accept the packet on a protected or working interface. Up to 8 alphanumeric characters are accepted.
Default
Authentication is disabled.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps authenticate command to ensure that only valid packets are accepted on the OOB communication channel.
The aps authenticate command must be configured on both the working and protect interfaces.
Examples
The following example enables authentication on POS interface 0 in slot 4:
router# configure terminalrouter(config)# interface pos 4/0/0router(config-if)# aps working 1router(config-if)# aps authenticate sanjoserouter(config-if)# exitrouter(config)# exitrouter#Related Commands
aps force
To manually switch the specified circuit to a protect interface, unless a request of equal or higher priority is in effect, use the aps force interface configuration command. To cancel the switch, use the no form of the command.
aps force circuit-number
no aps force circuit-numberSyntax Description
Default
No circuit is switched.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps force command to manually switch the interface to a protect interface when you are not using the aps revert command. For example, if you need to change the fiber connection, you can manually force the working interface to switch to the protect interface.
In a one-plus-one (1+1) configuration only, you can use the aps force 0 command to force traffic from the protect interface back onto the working interface.
The aps force command has a higher priority than any of the signal failures or the aps manual command.
The aps force command is configured only on protect interfaces.
Examples
The following example forces the circuit on POS interface 0 in slot 3 (a protect interface) back onto a working interface:
router# configure terminalrouter(config)# interface pos 3/0/0router(config-if)# aps protect 1router(config-if)# aps force 1router(config-if)# exitrouter(config)# exitrouter#Related Commands
aps manual
aps protect
aps workingaps group
To allow more than one protect and working interface to be supported on a router, use the aps group interface configuration command. To remove a group, use the no form of the command.
aps group group-number
no aps group group-numberSyntax Description
Default
No groups exist.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps group command to specify more than one working and protect interfaces on a router. For example, working channel for group 0 and protect channel for group 1 on one router and working channel for group 1 and protect channel for group 0 on another router.
The aps group command must be configured on both the protect and working interfaces.
Examples
The following example configures two working/protect interface pairs. Working interface (3/0/0) is configured in group 10 (the protect interface for this working interface is configured on another router), and protect interface (2/0/1) is configured in group 20:
router# configure terminalrouter(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.6 255.255.255.0router(config)# interface pos 3/0/0router(config-if)# aps group 10router(config-if)# aps working 1router(config)# interface pos 2/0/1router(config-if)# aps group 20router(config-if)# aps protect 1 7.7.7.7router(config-if)# endOn the second router, protect interface (4/0/0) is configured in group 10, and working interface (5/0/0) is configured in group 20 (the protect interface for this working interface is configured on another router):
router(config)# interface ethernet 0/0router(config-if)# ip address 7.7.7.7 255.255.255.0router(config)# interface pos 4/0/0router(config-if)# aps group 10router(config-if)# aps protect 1 7.7.7.6router(config)# interface pos 5/0/0router(config-if)# aps group 20router(config-if)# aps working 1router(config)# endrouter#Related Commands
aps lockout
To prevent a working interface from switching to a protect interface, use the aps lockout interface configuration command. To remove the lockout, use the no form of the command.
aps lockout circuit-number
no aps lockout circuit-numberSyntax Description
Default
No lockout exists.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
The aps lockout command is configured only on protect interfaces.
Examples
The following example locks out (that is, prevents the circuit from switching to a protect interface in the event that the working circuit becomes unavailable) the POS interface 3/0/0:
router# configure terminalrouter(config)# interface pos 3/0/0router(config-if)# aps protect 1 7.7.7.7router(config-if)# aps lockout 1router(config-if)# endrouter#Related Commands
aps manual
To manually switch a circuit to a protect interface, use the aps manual interface configuration command. To cancel the switch, use the no form of the command.
aps manual circuit-number
no aps manual circuit-numberSyntax Description
Default
No circuit is switched.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps manual command to manually switch the interface to a protect interface. For example, you can use this feature when you need to perform maintenance on the working channel. If a protection switch is already up, you can also use the aps manual command to revert the communication link back to the working interface before the wait to restore (WTR) time has expired. The WTR time period is set by the aps revert command.
In a one-plus-one (1+1) configuration only, you can use the aps manual 0 command to force traffic from the protect interface back onto the working interface.
The aps manual command is a lower priority than any of the signal failures or the aps force command.
Examples
The following example forces the circuit on POS interface 0 in slot 3 (a working interface) back onto the protect interface:
router# configure terminalrouter(config)# interface pos 3/0/0router(config-if)# aps working 1router(config-if)# aps manual 1router(config-if)# endrouter#Related Commands
aps force
aps protect
aps revert
aps workingaps protect
To enable a POS interface as a protect interface, use the aps protect interface command. To remove the POS interface as a protect interface, use the no form of the command.
aps protect circuit-number ip-address
no aps protect circuit-number ip-addressSyntax Description
circuit-number
Number of the circuit to enable as a protect interface.
ip-address
IP address of the router that has the working POS interface.
Default
No circuit is protected.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps protect command to configure the POS interface used by a working interface if the working interface becomes unavailable due to a router failure, degradation or loss of channel signal, or manual intervention.
Note
Examples
The following example configures circuit 1 on POS interface 5/0/0 as a protect interface for the working interface on the router with the IP address of 7.7.7.7. For information on how to configure the working interface, refer to the aps working command.
router# configure terminalrouter(config)# interface pos 5/0/0router(config-if)# aps protect 1 7.7.7.7router(config-if)# endrouter#Related Commands
aps revert
To enable automatic switchover from the protect interface to the working interface after the working interface becomes available, use the asp revert interface command. To disable automatic switchover, use the no form of the command.
aps revert minutes
no aps revertSyntax Description
minutes
Number of minutes until the circuit is switched back to the working interface after the working interface is available.
Default
Automatic switchover is disabled.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps revert command to return the circuit to the working interface when it becomes available.
The asp revert command is configured only on protect interfaces.
Examples
The following example enables circuit 1 on POS interface 5/0/0 to revert to the working interface after the working interface has been available for 3 minutes:
router# configure terminalrouter(config)# interface pos 5/0/0router(config-if)# aps protect 1 7.7.7.7router(config-if)# aps revert 3router(config-if)# endrouter#Related Commands
aps timers
To change the time between hello packets and the time before the protect interface process declares a working interface's router to be down, use the aps timers interface configuration command. To return to the default timers, use the no form of the command.
aps timers seconds1 seconds2
no aps timersSyntax Description
Default
Hello time is 1 second, and hold time is 3 seconds.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps timers command to control the time between an automatic switchover from the protect interface to the working interface after the working interface becomes available.
Normally, the hold time is greater than or equal to three times the hello time.
The aps timers command is configured only on protect interfaces.
Examples
The following example specifies a hello time of 2 seconds and a hold time of 6 seconds on circuit 1 on POS interface 5/0/0:
router# configure terminalrouter(config)# interface pos 5/0/0router(config-if)# aps working 1router(config-if)# aps timers 2 6router(config-if)# endrouter#aps unidirectional
To configure a protect interface for unidirectional mode, use the aps unidirectional interface configuration command. To return to the default, bidirectional mode, use the no form of the command.
aps unidirectional
no aps unidirectionalSyntax Description
This command has no keywords or arguments
Default
Bidirectional mode.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Use the aps unidirectional command when you must interoperate with SONET network equipment (ADMs) that supports unidirectional mode.
Note
The asp unidirectional command is configured only on protect interfaces.
Examples
The following example configures POS interface 3/0/0 for unidirectional mode:
router# configure terminalrouter(config)# interface pos 3/0/0router(config-if)# aps unidirectionalrouter(config-if)# aps protect 1 7.7.7.7router(config-if)# endrouter#aps working
To configure a POS interface as a working interface, use the aps working interface command. To remove the protect from the POS interface, use the no form of the command.
aps working circuit-number
no aps working circuit-numberSyntax Description
Default
No circuit is configured as working.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
When a working interface becomes unavailable because of a router failure, degradation or loss of channel signal, or manual intervention, the circuit is switched to the protect interface to maintain the connection.
To enable the circuit on the protect interface to switch back to the working interface after the working interface becomes available again, use the aps revert interface configuration command.
Note
Examples
The following example configures the POS interface 0 in slot 4 as a working interface. For information on how to configure the protect interface, refer to the aps protect command.
router# configure terminalrouter(config)# interface pos 4/0/0router(config-if)# aps working 1router(config-if)# endrouter#Related Commands
pos report
To permit selected SONET alarms to be logged to the console for a POS interface, use the pos report interface command. To disable logging of select SONET alarms, use the no form of this command.
pos report {b1-tca | b2-tca | b3-tca | lais | lrdi | pais | plop | prdi | rdool | sd-ber | sf-ber |
slof | slos}
no pos report {b1-tca | b2-tca | b3-tca | lais | lrdi | pais | plop | prdi | rdool | sd-ber | sf-ber |
slof | slos}Syntax Description
Default
b1-tca, b2-tca, b3-tca, plop, sf-ber, slof, and slos are reported by default.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Reporting an alarm means that the alarm can be logged to the console. Just because an alarm is permitted to be logged does not guarantee that it is logged. SONET alarm hierarchy rules dictate that only the most severe alarm of an alarm group is reported. Whether an alarm is reported or not, you can view the current state of a defect by checking the "Active Defects" line from the show controllers pos command output. A defect is a problem indication that is a candidate for an alarm.
For B1, the bit interleaved parity error report is calculated by comparing the BIP-8 code with the BIP-8 code extracted from the B1 byte of the following frame. Differences indicate that section level bit errors have occurred.
For B2, the bit interleaved parity error report is calculated by comparing the BIP-8/24 code with the BIP-8 code extracted from the B2 byte of the following frame. Differences indicate that line level bit errors have occurred.
For B3, the bit interleaved parity error report is calculated by comparing the BIP-8 code with the BIP-8 code extracted from the B3 byte of the following frame. Differences indicate that path level bit errors have occurred.
PAIS is sent by line terminating equipment (LTE) to alert the downstream path terminating equipment (PTE) that it has detected a defect on its incoming line signal.
PLOP is reported as a result of an invalid pointer (H1, H2) or an excess number of new data flag (NDF) enabled indications.
SLOF is detected when a severely error framing (SEF) defect on the incoming SONET signal persists for 3 milliseconds.
SLOS is detected when an all-zeros pattern on the incoming SONET signal lasts 19(+-3) microseconds or longer. This defect might also be reported if the received signal level drops below the specified threshold.
To determine the alarms that are reported on the interface, use the show controllers pos command.
Example
The following example enables reporting of SD-BER and LAIS alarms on the interface:
Router(config)# interface pos 3/0/0Router(config-if)# pos report sd-berRouter(config-if)# pos report laisRouter(config-if)# endRouter#Related Commands
interface pos
show controllers pospos threshold
To set the BER threshold values of the specified alarms for a POS interface, use the pos threshold interface command. To return to the default setting, use the no form of this command.
pos threshold {b1-tca | b2-tca | b3-tca | sd-ber | sf-ber} rate
no pos threshold {b1-tca | b2-tca | b3-tca | sd-ber | sf-ber} rateSyntax Description
Default
The default is 6 for b1-tca, b2-tca, b3-tca, and sd-ber. The default is 3 for sf-ber.
Command Mode
Interface configuration
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
For B1, the bit interleaved parity error report is calculated by comparing the BIP-8 code with the BIP-8 code extracted from the B1 byte of the following frame. Differences indicate that section level bit errors have occurred.
For B2, the bit interleaved parity error report is calculated by comparing the BIP-8/24 code with the BIP-8 code extracted from the B2 byte of the following frame. Differences indicate that line level bit errors have occurred.
For B3, the bit interleaved parity error report is calculated by comparing the BIP-8 code with the BIP-8 code extracted from the B3 byte of the following frame. Differences indicate that path level bit errors have occurred.
SF-BER and SD-BER are sourced from B2 BIP-8 error counts (as is B2-TCA). However, SF-BER and SD-BER feed into the APS machine and can lead to a protection switch (if APS is configured).
B1-TCA, B2-TCA, and B3-TCA do nothing more than print a log message to the console (if reports for them are enabled).
To determine the BER thresholds configured on the interface, use the show controllers pos command.
Example
The following example configures thresholds on the interface:
Router(config)# interface pos 3/0/0Router(config-if)# pos threshold sd-ber 8Router(config-if)# pos threshold sf-ber 4Router(config-if)# pos threshold b1_tca 4Router(config-if)# endRouter#Related Commands
interface pos
show controllers posshow aps
To display information about the current automatic protection switching (APS) feature, use the show aps EXEC command.
show aps
Syntax Description
This command has no arguments or keywords.
Command Mode
Privileged EXEC
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC.
Sample Displays
The following is sample output of the show aps command on a router configured with a working interface. In this example, POS interface 0/0/0 is configured as a working interface in group 1, and the interface is selected (that is, active).
router1# show apsPOS0/0/0 working group 1 channel 1 Enabled SelectedThe following is sample output of the show aps command on a router configured with a protect interface. In this example, POS interface 2/0/0 is configured as a protect interface in group 1, and the interface is not selected (the ~ indicates that the interface is not active). The output also shows that the working channel is located on the router with the IP address 15.1.6.1 and that the interface is currently selected (that is, active).
router2# show apsPOS2/0/0 protect group 1 channel 0 bidirectional ~SelectedRx_K1= 0, Rx_K2= 0 Tx_K1= 0 Tx_K2= 5Working channel 1 at 15.1.6.1 EnabledFor the K1 field (8 bits), the first 4 bits indicate the channel number that has made the request, and the last 4 bits map to the the requests (local or external) listed in . For K2 field (8 bits), the first 4 bits indicate the channel number bridged onto the protect line, the next bit is the architecture used, and the last 3 bits indicate the mode of operation or non-APS use listed in .
Related Commands
show controllers pos
To display information about the POS controllers, use the show controllers pos privileged EXEC command.
show controllers pos [slot-number] [details]
Syntax Description
Command Mode
Privileged EXEC
Usage Guidelines
This command first appeared in Cisco IOS Release 11.1 CC and 11.2 GS.
The information displayed is generally useful for diagnostic tasks performed by technical support personnel only.
Sample Display
The following is sample output of the show controllers pos command on a Cisco 7500 series router:
router# show controllers posPOS2/0/0SECTIONLOF = 0 LOS = 2335 BIP(B1) = 77937133LINEAIS = 2335 RDI = 20 FEBE = 3387950089 BIP(B2) = 1622825387PATHAIS = 2340 RDI = 66090 FEBE = 248886263 BIP(B3) = 103862953LOP = 246806 NEWPTR = 11428072 PSE = 5067357 NSE = 4645Active Defects: B2-TCA B3-TCAActive Alarms: NoneAlarm reporting enabled for: B1-TCAAPSCOAPS = 12612784 PSBF = 8339State: PSBF_state = FalseRx(K1/K2): 00/CC Tx(K1/K2): 00/00S1S0 = 03, C2 = 96CLOCK RECOVERYRDOOL = 64322060State: RDOOL_state = TruePATH TRACE BUFFER: UNSTABLERemote hostname :Remote interface:Remote IP addr :Remote Rx(K1/K2): ../.. Tx(K1/K2): ../..BER thresholds: SF = 10e-3 SD = 10e-8TCA thresholds: B1 = 10e-7 B2 = 10e-3 B3 = 10e-6router#describes the fields shown in the display.
Guest
