SPA interface ports begin numbering with “0” from left to right. Single-port SPAs use only the port number 0. To configure or monitor SPA interfaces, you need to specify the physical location of the SIP, SPA, and interface in the CLI. The interface address format is slot/subslot/port, where:

• slot—Specifies the chassis slot number in the Cisco ASR 1000 Series Router where the SIP is installed.

• subslot—Specifies the secondary slot of the SIP where the SPA is installed.

• port—Specifies the number of the individual interface port on a SPA.

The following example shows how to specify the first interface (0) on a SPA installed in the first subslot of a SIP (0) installed in chassis slot 2:

Router(config)# interface serial 2/0/0

This command shows a serial SPA as a representative example, however the same slot/subslot/port format is similarly used for other SPAs (such as ATM and POS) and other non-channelized SPAs.

For more information about identifying slots and subslots, see the Configuring the Encapsulation Type.

The Cisco IOS software supports three different types of configurable maximum transmission unit (MTU) options at different levels of the protocol stack:

• Interface MTU—Checked by the SPA on traffic coming in from the network. Different interface types support different interface MTU sizes and defaults. The interface MTU defines the maximum packet size allowable (in bytes) for an interface before drops occur. If the frame is smaller than the interface MTU size, but is not smaller than three bytes of payload size, then the frame continues to process.
• IP MTU—Can be configured on a subinterface and is used by the Cisco IOS software to determine whether fragmentation of a packet takes place. If an IP packet exceeds the IP MTU size, then the packet is fragmented.
• Tag or Multiprotocol Label Switching (MPLS) MTU—Can be configured on a subinterface and allows up to six different labels, or tag headers, to be attached to a packet. The maximum number of labels is dependent on your Cisco IOS software release.

Different encapsulation methods and the number of MPLS MTU labels add additional overhead to a packet. For example, for an Ethernet packet, SNAP encapsulation adds an 8-byte header, dot1q encapsulation adds a 2-byte header, and each MPLS label adds a 4-byte header (n labels x 4 bytes).

Note	In the Cisco ASR 1000 Series Route Processor 1 (RP1), 2RU and 2RU-Fixed chassis, the MTU size for the Management Ethernet interface (interface gigabitethernet 0) is limited to 2370 bytes.

POS framing can be specified as SONET (Synchronous Optical Network) or SDH (Synchronous Digital Hierarchy). SONET and SDH are a set of related standards for synchronous data transmission over fiber- optic networks. SONET is the United States version of the standard published by the American National Standards Institute (ANSI). SDH is the international version of the standard published by the International Telecommunications Union (ITU).

To modify the POS framing, use the following command in interface configuration mode:

To return to the default, use the no form of the command.

When the keepalive feature is enabled, a keepalive packet is sent at the specified time interval to keep the interface active. The keepalive interval must be configured to be the same on both ends of the POS link.

To modify the keepalive interval, use the following command in interface configuration mode:

To disable keepalive packets, use the no form of this command.

Note

If keepalives are enabled and you are trying to configure line loopback on a POS interface, the keepalive protocol will fail and periodically reset the interface based on the keepalive timeout and cause Layer 1 errors on the other end of the link that is trying to do the loopbacks.You can avoid this by using the no keepalive command on the POS interface that is configured for line loopback. The side that is not in line loopback detects that its keepalive is being looped back and functions properly. An interface configured for internal loopback also functions properly with keepalives enabled.

CRC is an error-checking technique that uses a calculated numeric value to detect errors in transmitted data. The CRC size indicates the length in bits of the FCS.

The CRC size must be configured to be the same on both ends of the POS link.

To modify the CRC size, use the following command in interface configuration mode:

To return to the default CRC size, use the no form of the command.

A clock source of internal specifies that the interface clocks its transmitted data from its internal clock. A clock source of line specifies that the interface clocks its transmitted data from a clock recovered from the line’s receive data stream.

For information about the recommended clock source settings for POS router interfaces, refer to Configuring Clock Settings on POS Router Interfaces at the following URL:

http:/​/​www.cisco.com/​en/​US/​tech/​tk482/​tk607/​technologies_​tech_​note09186a0080094bb9.shtml

To modify the clock source, use the following command in interface configuration mode:

To return to the default clock source, use the no form of this command.

SONET payload scrambling applies a self-synchronous scrambler (x43+1) to the Synchronous Payload Envelope (SPE) of the interface to ensure sufficient bit transition density.

The default configuration is SONET payload scrambling disabled.

SONET payload scrambling must be configured to be the same on both ends of the POS link.

To modify SONET payload scrambling, use the following command in interface configuration mode:

To disable SONET payload scrambling, use the no form of this command.

By default, the POS interfaces support High-Level Data Link Control (HDLC) encapsulation. The encapsulation method can be specified as HDLC, Point-to-Point Protocol (PPP), or Frame Relay. The encapsulation type must be configured to be the same on both ends of the POS link.

To modify the encapsulation method, use the following command in interface configuration mode:

A trigger is an alarm that, when activated, causes the line protocol to go down. The POS alarm trigger delay helps to ensure uptime of a POS interface by preventing intermittent problems from disabling the line protocol. The POS alarm trigger delay feature delays the setting of the line protocol to down when trigger alarms are received. If the trigger alarm was sent because of an intermittent problem, the POS alarm trigger delay can prevent the line protocol from going down when the line protocol is functional.

To save your running configuration to nonvolatile random-access memory (NVRAM), use the following command in privileged EXEC configuration mode:

For more information about managing your system image and configuration files, refer to the Cisco IOS XE Configuration Fundamentals Configuration Guide and Cisco IOS Configuration Fundamentals Command Reference publications that correspond to your Cisco IOS XE software release.

You can shut down and restart any of the interface ports on a SPA independently of each other. Shutting down an interface stops traffic and then enters the interface into an “administratively down” state.

If you are preparing for an OIR of a SPA, it is not necessary to independently shut down each of the interfaces prior to deactivation of the SPA. You do not need to independently restart any interfaces on a SPA after OIR of a SPA or SIP. For more information about performing an OIR for a SPA, see the Configuring the Encapsulation Type.

To shut down an interface on a SPA, use the following command in interface configuration mode:

To restart an interface on a SPA, use the following command in interface configuration mode:

To find detailed interface information on a per-port basis for the POS SPAs, use the show interfaces pos command. For an example of the command output for a POS SPA at location 0/3/0, see the following:

router# show interfaces POS 0/3/0
POS0/3/0 is administratively down, line protocol is down 
  Hardware is Packet over Sonet
  MTU 4470 bytes, BW 155000 Kbit, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, crc 16, loopback not set
  Keepalive set (10 sec)
  Scramble disabled
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
              0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 applique, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions

To find detailed alarm and error information on a per-port basis for the POS SPAs, use the show controllers pos command. For an example of the command output for a POS SPA at location 0/3/0, see the following:

router# show controllers pos
POS0/3/0
SECTION
  LOF = 0          LOS    = 0                            BIP(B1) = 0
LINE
  AIS = 0          RDI    = 0          FEBE = 0          BIP(B2) = 0
PATH
  AIS = 0          RDI    = 0          FEBE = 0          BIP(B3) = 0
  PLM = 0          UNEQ   = 0          TIM  = 0          TIU     = 0
  LOP = 0          NEWPTR = 0          PSE  = 0          NSE     = 0
Active Defects: None
Active Alarms: None
Alarm reporting enabled for: SF SLOS SLOF B1-TCA B2-TCA PLOP B3-TCA 
Framing: SONET
APS
  COAPS = 0          PSBF = 0         
  State: PSBF_state = False
  Rx(K1/K2): 00/00  Tx(K1/K2): 00/00
  Rx Synchronization Status S1 = 00
  S1S0 = 00, C2 = 00
  Remote aps status (none); Reflected local aps status (none)
 --More--                           CLOCK RECOVERY
  RDOOL = 0         
  State: RDOOL_state = False
PATH TRACE BUFFER: UNSTABLE
  Remote hostname : 
  Remote interface: 
  Remote IP addr  : 
  Remote Rx(K1/K2):   /    Tx(K1/K2):   /  
BER thresholds: SF = 10e-3 SD = 10e-6
TCA thresholds: B1 = 10e-6 B2 = 10e-6 B3 = 10e-6
  Clock source: line

The following example shows how to enter global configuration mode to specify the interface that you want to configure, configure an IP address for the interface, enable the interface, and save the configuration. This example configures interface port 0 (the first port) of the SPA located in subslot 0 of the SIP that is installed in slot 2 of the Cisco ASR 1000 Series Router:

!Enter global configuration mode

!

Router# configure terminal

! 

! Specify the interface address

!

Router(config)# interface pos 2/0/0

!

! Configure an IP address

!

Router(config-if)# ip address 192.168.50.1 192.255.255.0

!

! Enable the interface

!

Router(config-if)# no shutdown

!

! Save the configuration to NVRAM

!

Router(config-if)# exit

Router# copy running-config startup-config

The following example sets the MTU to 4470 bytes on interface port 1 (the second port) of the SPA located in the bottom subslot (1) of the SIP that is installed in slot 2 of the Cisco ASR 1000 Series Router:

!Enter global configuration mode

!

Router# configure terminal

! 

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

! Configure MTU

!

Router(config-if)# mtu 4470

The following example shows how to change from the default POS framing of SONET to SDH:

!Enter global configuration mode

!

Router# configure terminal

!

! Specify the interface address

!

Router(config)# interface pos 2/1/1

! (The default pos framing is sonet)

!

!Modify the framing type

!

Router(config-if)# pos framing sdh

The following example shows how to change from the default keepalive period of 10 seconds to 20 seconds:

!Enter global configuration mode

!

Router# configure terminal

!

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

! Configure keepalive 20

!

Router(config-if)# keepalive 20 

The following example shows how to change the CRC size from 32 bits to the default 16 bits for POS SPAs:

!Enter global configuration mode

!

Router# configure terminal

! 

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

! Configure crc 16

!

Router(config-if)# crc 16

The following example shows how to change from the default clock source of internal to line:

!Enter global configuration mode

!

Router# configure terminal

! 

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

! Configure the clock source

!

Router(config-if)# clock source line

The following example shows how to change from a default SONET payload scrambling of disabled to enabled:

!Enter global configuration mode

! 

Router# configure terminal

!

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

! Configure the SONET payload scrambling

!

Router(config-if)# pos scramble-atm

The following example shows how to change from the default encapsulation method of HDLC to PPP:

!Enter global configuration mode

!

Router# configure terminal

! Specify the interface address

Router(config)# interface pos 2/1/1

!

! Configure ppp

!

Router(config-if)# encapsulation ppp

The following example shows how to change POS line-level and path-level alarm trigger delays from the default of 100 milliseconds to 200 milliseconds:

!Enter global configuration mode

!

Router# configure terminal

! 

! Specify the interface address

!

Router(config)# interface pos 2/1/1

!

Router(config-if)# pos delay triggers line 200

Router(config-if)# pos delay triggers path 200