Cisco ASR 9000 Series Aggregation Services Router Interface and Hardware Component Configuration Guide
Configuring Serial Interfaces on the Cisco ASR 9000 Series Router
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Configuring Serial Interfaces on the Cisco ASR 9000 Series Router

Table Of Contents

Configuring Serial Interfaces on the Cisco ASR 9000 Series Router

Contents

Prerequisites for Configuring Serial Interfaces

Information About Serial Interfaces

Serial Interface Concepts

Cisco HDLC Encapsulation

PPP Encapsulation

Multilink PPP

Keepalive Timer

Default Settings for Serial Interface Configurations

Serial Interface Naming Notation

How to Configure Serial Interfaces

Bringing Up a Serial Interface

Prerequisites

Restrictions

What to Do Next

Configuring Optional Serial Interface Parameters

Prerequisites

Restrictions

What to Do Next

Modifying the Keepalive Interval on Serial Interfaces

Prerequisites

Restrictions

Configuration Examples for Serial Interfaces

Configuring a Serial Interface with PPP Encapsulation: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance


Configuring Serial Interfaces on the Cisco ASR 9000 Series Router


This module describes the configuration of serial interfaces on the Cisco ASR 9000 Series Router.

Feature History for Configuring Serial Controller Interfaces

Release
Modification

Release 3.9.0

Support for serial interfaces was added on the Cisco ASR 9000 Series Router.


Contents

Prerequisites for Configuring Serial Interfaces

Information About Serial Interfaces

Serial Interface Concepts

How to Configure Serial Interfaces

Configuration Examples for Serial Interfaces

Additional References

Prerequisites for Configuring Serial Interfaces

You must be in a user group associated with a task group that includes the proper task IDs. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

The Cisco ASR 9000 Series Router supports serial interfaces on the followig hardware:

SIP 700 SPA Interface Processor

2-Port Channelized OC-12c/DS0 SPA

Information About Serial Interfaces

To configure serial interfaces, you must understand the following concepts:

Cisco HDLC Encapsulation

PPP Encapsulation

Keepalive Timer

Default Settings for Serial Interface Configurations

Serial Interface Naming Notation

Serial Interface Concepts

To configure serial interfaces, you must understand the following concepts:

Cisco HDLC Encapsulation

PPP Encapsulation

Keepalive Timer

Cisco HDLC Encapsulation

Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over synchronous serial links using HDLC. Cisco HDLC also provides a simple control protocol called Serial Line Address Resolution Protocol (SLARP) to maintain serial link keepalives. HDLC is the default encapsulation type for serial interfaces under Cisco IOS XR software. Cisco HDLC is the default for data encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet delineation and error control.


Note Cisco HDLC is the default encapsulation type for the serial interfaces.


Cisco HDLC uses keepalives to monitor the link state, as described in the "Keepalive Timer" section.


Note Use the debug chdlc slarp packet command to display information about the Serial Line Address Resolution Protocol (SLARP) packets that are sent to the peer after the keepalive timer has been configured.


PPP Encapsulation

PPP is a standard protocol used to send data over synchronous serial links. PPP also provides a Link Control Protocol (LCP) for negotiating properties of the link. LCP uses echo requests and responses to monitor the continuing availability of the link.


Note When an interface is configured with PPP encapsulation, a link is declared down, and full LCP negotiation is re-initiated after five ECHOREQ packets are sent without receiving an ECHOREP response.


PPP provides the following Network Control Protocols (NCPs) for negotiating properties of data protocols that will run on the link:

IP Control Protocol (IPCP) to negotiate IP properties

Multiprotocol Label Switching control processor (MPLSCP) to negotiate MPLS properties

Cisco Discovery Protocol control processor (CDPCP) to negotiate CDP properties

IPv6CP to negotiate IP Version 6 (IPv6) properties

Open Systems Interconnection control processor (OSICP) to negotiate OSI properties

PPP uses keepalives to monitor the link state, as described in the "Keepalive Timer" section.

PPP supports the following authentication protocols, which require a remote device to prove its identity before allowing data traffic to flow over a connection:

Challenge Handshake Authentication Protocol (CHAP)—CHAP authentication sends a challenge message to the remote device. The remote device encrypts the challenge value with a shared secret and returns the encrypted value and its name to the local router in a response message. The local router attempts to match the remote device's name with an associated secret stored in the local username or remote security server database; it uses the stored secret to encrypt the original challenge and verify that the encrypted values match.

Microsoft Challenge Handshake Authentication Protocol (MS-CHAP)—MS-CHAP is the Microsoft version of CHAP. Like the standard version of CHAP, MS-CHAP is used for PPP authentication; in this case, authentication occurs between a personal computer using Microsoft Windows NT or Microsoft Windows 95 and a Cisco router or access server acting as a network access server.

Password Authentication Protocol (PAP)—PAP authentication requires the remote device to send a name and a password, which are checked against a matching entry in the local username database or in the remote security server database.


Note For more information on enabling and configuring PPP authentication protocols, see the Configuring PPP on the Cisco ASR 9000 Series Router module in this manual.


Use the ppp authentication command in interface configuration mode to enable CHAP, MS-CHAP, and PAP on a serial interface.


Note Enabling or disabling PPP authentication does not effect the local router's willingness to authenticate itself to the remote device.


Multilink PPP

Multilink Point-to-Point Protocol (MLPPP) is supported on the 2-Port Channelized OC-12/DS0 SPA. MLPPP provides a method for combining multiple physical links into one logical link. The implementation of MLPPP combines multiple PPP serial interfaces into one multilink interface. MLPPP performs the fragmenting, reassembling, and sequencing of datagrams across multiple PPP links.

MLPPP provides the same features that are supported on PPP Serial interfaces with the exception of QoS. It also provides the following additional features:

Fragment sizes of 128, 256, and 512 bytes

Long sequence numbers (24-bit)

Lost fragment detection timeout period of 80 ms

Minimum-active-links configuration option

LCP echo request/reply support over multilink interface

Full T1 framed and unframed links

For more information about configuring MLPPP on a serial interface, see the Configuring PPP on the Cisco ASR 9000 Series Router module in this document.

Keepalive Timer

Cisco keepalives are useful for monitoring the link state. Periodic keepalives are sent to and received from the peer at a frequency determined by the value of the keepalive timer. If an acceptable keepalive response is not received from the peer, the link makes the transition to the down state. As soon as an acceptable keepalive response is obtained from the peer or if keepalives are disabled, the link makes the transition to the up state.


Note The keepalive command applies to serial interfaces using HDLC or PPP encapsulation. It does not apply to serial interfaces using Frame Relay encapsulation.


For each encapsulation type, a certain number of keepalives ignored by a peer triggers the serial interface to transition to the down state. For HDLC encapsulation, three ignored keepalives causes the interface to be brought down. For PPP encapsulation, five ignored keepalives causes the interface to be brought down. ECHOREQ packets are sent out only when LCP negotiation is complete (for example, when LCP is open).

Use the keepalive command in interface configuration mode to set the frequency at which LCP sends ECHOREQ packets to its peer. To restore the system to the default keepalive interval of 10 seconds, use the keepalive command with no argument. To disable keepalives, use the keepalive disable command. For both PPP and Cisco HDLC, a keepalive of 0 disables keepalives and is reported in the show running-config command output as keepalive disable.

When LCP is running on the peer and receives an ECHOREQ packet, it responds with an echo reply (ECHOREP) packet, regardless of whether keepalives are enabled on the peer.

Keepalives are independent between the two peers. One peer end can have keepalives enabled; the other end can have them disabled. Even if keepalives are disabled locally, LCP still responds with ECHOREP packets to the ECHOREQ packets it receives. Similarly, LCP also works if the period of keepalives at each end is different.


Note Use the debug chdlc slarp packet command and other Cisco HDLC debug commands to display information about the Serial Line Address Resolution Protocol (SLARP) packets that are sent to the peer after the keepalive timer has been configured.


Default Settings for Serial Interface Configurations

When an interface is enabled on a T3/E3 SPA, and no additional configuration commands are applied, the default interface settings shown in Table 7 are present. These default settings can be changed by configuration.

Table 7 Serial Interface Default Settings

Parameter
Configuration File Entry
Default Settings

Keepalive

Note The keepalive command applies to serial interfaces using HDLC or PPP encapsulation. It does not apply to serial interfaces using Frame Relay encapsulation.

keepalive [disable]
no keepalive

keepalive 10 seconds

Encapsulation

encapsulation [hdlc | ppp | ]

hdlc

Maximum transmission unit (MTU)

mtu bytes

1504 bytes

Cyclic redundancy check (CRC)

crc [16 | 32]

16

Data stream inversion on a serial interface

invert

Data stream is not inverted

Payload scrambling (encryption)

scramble

Scrambling is disabled.

Number of High-Level Data Link Control (HDLC) flag sequences to be inserted between the packets

transmit-delay

Default is 0 (disabled).



Note Default settings do not appear in the output of the show running-config command.


Serial Interface Naming Notation

The naming notation for T1 interfaces on a channelized SPA is rack/slot/module/port/channel-num:channel-group-number, as shown in the following example:

interface serial 0/0/1/2/4:3
 
   

If a subinterface are configured under the serial interface, then the router includes the subinterface number at the end of the serial interface address. In this case, the naming notation is rack/slot/module/port[/channel-num:channel-group-number].subinterface, as shown in the following examples:

interface serial 0/0/1/2.1
interface serial 0/0/1/2/4:3.1

Note A slash between values is required as part of the notation.


The naming notation syntax for serial interfaces is as follows:

rack: Chassis number of the rack.

slot: Physical slot number of the modular services card or line card.

module: Module number. Shared port adapters (SPAs) are referenced by their subslot number.

port: Physical port number of the controller.

channel-num: T1 channel number. T1 channels range from 0 to 23;

channel-group-number: Time slot number. T1 time slots range from 1 to 24; The channel-group-number is preceded by a colon and not a slash.

subinterface: Subinterface number.

Use the question mark (?) online help function following the serial keyword to view a list of all valid interface choices.

How to Configure Serial Interfaces

The following tasks describe how to configure a serial interface:

Bringing Up a Serial Interface

Configuring Optional Serial Interface Parameters

Modifying the Keepalive Interval on Serial Interfaces

Bringing Up a Serial Interface

This task describes the commands you can use to bring up a serial interface.

Prerequisites

The Cisco ASR 9000 Series Router must have the following SIP and SPA installed and running Cisco IOS XR software:

SIP 700 SPA Interface Processor

2-Port Channelized OC-12c/DS0 SPA

Restrictions

The configuration on both ends of the serial connection must match for the interface to be active.

SUMMARY STEPS

1. show interfaces

2. configure

3. interface serial interface-path-id

4. ipv4 address ip-address

5. no shutdown

6. end
or
commit

7. exit

8. exit

9. Repeat Step 1 through Step 8 to bring up the interface at the other end of the connection.

10. show ipv4 interface brief

11. show interfaces serial interface-path-id

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

show interfaces

Example:

RP/0/0/CPU0:router# show interfaces

(Optional) Displays configured interfaces.

Use this command to also confirm that the router recognizes the PLIM card.

Step 2 

configure

Example:

RP/0/0/CPU0:router# configure

Enters global configuration mode.

Step 3 

interface serial interface-path-id

Example:

RP/0/0/CPU0:router(config)# interface serial 0/1/0/0

Specifies the serial interface name and notation rack/slot/module/port, and enters interface configuration mode.

Step 4 

ipv4 address ip-address

Example:

RP/0/0/CPU0:router(config-if)# ipv4 address 10.1.2.1 255.255.255.224

Assigns an IP address and subnet mask to the interface.

Note Skip this step if you are configuring Frame Relay encapsulation on this interface. For Frame Relay, the IP address and subnet mask are configured under the subinterface.

Step 5 

no shutdown

Example:

RP/0/0/CPU0:router (config-if)# no shutdown

Removes the shutdown configuration.

Note Removal of the shutdown configuration eliminates the forced administrative down on the interface, enabling it to move to an up or down state (assuming the parent SONET layer is not configured administratively down).

Step 6 

end

or

commit

Example:

RP/0/0/CPU0:router (config-if)# end

or

RP/0/0/CPU0:router(config-if)# commit

Saves configuration changes.

When you issue the end command, the system prompts you to commit changes:

Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
 
        

Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 7 

exit

Example:

RP/0/0/CPU0:router (config-if)# exit

Exits interface configuration mode and enters global configuration mode.

Step 8 

exit

Example:

RP/0/0/CPU0:router (config)# exit

Exits global configuration mode and enters EXEC mode.

Step 9 

show interfaces

configure

interface serial interface-path-id

no shut

exit

exit

commit

Example:
RP/0/0/CPU0:router# show interfaces

RP/0/0/CPU0:router# configure

RP/0/0/CPU0:router (config)# interface serial 0/1/0/1

RP/0/0/CPU0:router(config-if)# ipv4 address 10.1.2.2 255.255.255.224

RP/0/0/CPU0:router (config-if)# no shutdown

RP/0/0/CPU0:router (config-if)# commit

RP/0/0/CPU0:router (config-if)# exit

RP/0/0/CPU0:router (config)# exit

Repeat Step 1 through Step 8 to bring up the interface at the other end of the connection.

Note The configuration on both ends of the serial connection must match.

Step 10 

show ipv4 interface brief

Example:

RP/0/0/CPU0:router # show ipv4 interface brief

Verifies that the interface is active and properly configured.

If you have brought up a serial interface properly, the "Status" field for that interface in the show ipv4 interface brief command output shows "Up."

Step 11 

show interfaces serial interface-path-id

Example:

RP/0/0/CPU0:router# show interfaces serial 0/1/0/0

(Optional) Displays the interface configuration.

What to Do Next

To modify the default configuration of the serial interface you just brought up, see the "Configuring Optional Serial Interface Parameters" section.

Configuring Optional Serial Interface Parameters

This task describes the commands you can use to modify the default configuration on a serial interface.

Prerequisites

Before you modify the default serial interface configuration, you must bring up the serial interface and remove the shutdown configuration, as described in the "Bringing Up a Serial Interface" section.

Restrictions

The configuration on both ends of the serial connection must match for the interface to be active.

SUMMARY STEPS

1. configure

2. interface serial interface-path-id

3. encapsulation [hdlc | ppp]

4. serial

5. crc length

6. invert

7. scramble

8. transmit-delay hdlc-flags

9. end
or
commit

10. exit

11. exit

12. exit

13. show interfaces serial [interface-path-id]

 
Command or Action
Purpose

Step 1 

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2 

interface serial interface-path-id

Example:

RP/0/RP0/CPU0:router(config)# interface serial 0/1/0/0

Specifies the serial interface name and notation rack/slot/module/port, and enters interface configuration mode.

Step 3 

encapsulation [hdlc | ppp ]

Example:

RP/0/RP0/CPU0:router(config-if)# encapsulation hdlc

(Optional) Configures the interface encapsulation parameters and details such as HDLC or PPP.

Note The default encapsulation is hdlc.

Step 4 

serial

Example:

RP/0/0/CPU0:router(config-if)# serial

RP/0/0/CPU0:ios(config-if-serial)#

(Optional) Enters serial submode to configure the serial parameters.

Step 5 

crc length

Example:

RP/0/0/CPU0:ios(config-if-serial)# crc 32

(Optional) Specifies the length of the cyclic redundancy check (CRC) for the interface. Enter the 16 keyword to specify 16-bit CRC mode, or enter the 32 keyword to specify 32-bit CRC mode.

Note The default is CRC length is 16.

Step 6 

invert

Example:

RP/0/0/CPU0:ios(config-if-serial)# inverts

(Optional) Inverts the data stream.

Step 7 

scramble

Example:

RP/0/0/CPU0:ios(config-if-serial)# scramble

(Optional) Enables payload scrambling on the interface.

Note Payload scrambling is disabled on the interface.

Step 8 

transmit-delay hdlc-flags

Example:

RP/0/0/CPU0:ios(config-if-serial)# transmit-delay 10

(Optional) Specifies a transmit delay on the interface. Values can be from 0 to 128.

Note Transmit delay is disabled by default (the transmit delay is set to 0).

Step 9 

end

or

commit

Example:

RP/0/RP0/CPU0:router (config-if)# end

or

RP/0/RP0/CPU0:router(config-if)# commit

Saves configuration changes.

When you issue the end command, the system prompts you to commit changes:

Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
 
        

Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 10 

exit

Example:

RP/0/0/CPU0:router(config-if-serial)# exit

RP/0/0/CPU0:router(config-if)#

Exits serial configuration mode.

Step 11 

exit

Example:

RP/0/RP0/CPU0:router (config-if)# exit

Exits interface configuration mode and enters global configuration mode.

Step 12 

exit

Example:

RP/0/RP0/CPU0:router (config)# exit

Exits global configuration mode and enters EXEC mode.

Step 13 

show interfaces serial [interface-path-id]

Example:

RP/0/RP0/CPU0:router# show interface serial 0/1/0/0

(Optional) Displays general information for the specified serial interface.

What to Do Next

To configure PPP authentication on serial interfaces with PPP encapsulation, see the Configuring PPP on the Cisco ASR 9000 Series Router module later in this manual.

To modify the default keepalive configuration, see the "Modifying the Keepalive Interval on Serial Interfaces" section.

Modifying the Keepalive Interval on Serial Interfaces

Perform this task to modify the keepalive interval on serial interfaces that have Cisco HDLC or PPP encapsulation enabled.


Note When you enable Cisco HDLC or PPP encapsulation on a serial interface, the default keepalive interval is 10 seconds. Use this procedure to modify that default keepalive interval.



Note Cisco HDLC is enabled by default on serial interfaces.


Prerequisites

Before you can modify the keepalive timer configuration, you must ensure that Cisco HDLC or PPP encapsulation is enabled on the interface. Use the encapsulation command to enable Cisco HDLC or PPP encapsulation on the interface, as described in the "Configuring Optional Serial Interface Parameters" section.

Restrictions

SUMMARY STEPS

1. configure

2. interface serial interface-path-id

3. keepalive {seconds | disable}
or
no keepalive

4. end
or
commit

5. show interfaces type interface-path-id

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

configure

Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2 

interface serial interface-path-id

Example:

RP/0/RP0/CPU0:router(config)# interface serial 0/1/0/0

Specifies the serial interface name and notation rack/slot/module/port and enters interface configuration mode.

Step 3 

keepalive {seconds | disable}

or

no keepalive

Example:
RP/0/RP0/CPU0:router(config-if)# keepalive 3

or

RP/0/RP0/CPU0:router(config-if)# no keepalive

Specifies the number of seconds between keepalive messages.

Use the keepalive disable command, the no keepalive, or the keepalive command with an argument of 0 to disable the keepalive feature.

Range is from 1 through 30 seconds.

Default is 10 seconds.

If keepalives are configured on an interface, use the no keepalive command to disable the keepalive feature before you configure Frame Relay encapsulation on that interface.

Step 4 

end

or

commit

Example:

RP/0/RP0/CPU0:router(config-if)# end

or

RP/0/RP0/CPU0:router(config-if)# commit

Saves configuration changes.

When you issue the end command, the system prompts you to commit changes:

Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
 
        

Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 5 

show interfaces serial interface-path-id

Example:

RP/0/RP0/CPU0:router# show interfaces serial 0/1/0/0

(Optional) Verifies the interface configuration.

Configuration Examples for Serial Interfaces

This section provides the following configuration examples:

Configuring a Serial Interface with PPP Encapsulation: Example

Configuring a Serial Interface with PPP Encapsulation: Example

The following example shows how to create and configure a serial interface with PPP encapsulation:

RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# interface serial 0/3/0/0/0:0
RP/0/RP0/CPU0:router(config-if)# ipv4 address 172.18.189.38 255.255.255.224
RP/0/RP0/CPU0:router(config-if)# encapsulation ppp
RP/0/RP0/CPU0:router(config-if)# no shutdown
RP/0/RP0/CPU0:router(config-if)# ppp authentication chap MIS-access
RP/0/RP0/CPU0:router(config-if)# end
Uncommitted changes found, commit them? [yes]: yes
 
   

The following example shows how to configure serial interface 0/3/0/0/0:0 to allow two additional retries after an initial authentication failure (for a total of three failed authentication attempts):

RP/0/RP0/CPU0:router# configuration
RP/0/RP0/CPU0:router(config)# interface serial 0/3/0/0/0:0
RP/0/RP0/CPU0:router(config-if)# encapsulation ppp
RP/0/RP0/CPU0:router(config-if)# ppp authentication chap
RP/0/RP0/CPU0:router(config-if)# ppp max-bad-auth 3
RP/0/RP0/CPU0:router(config-if)# end
Uncommitted changes found, commit them? [yes]: yes
 
   

Additional References

The following sections provide references related to T3/E3 and T1/E1 controllers and serial interfaces.

Related Documents

Related Topic
Document Title

Cisco IOS XR master command reference

Cisco IOS XR Master Commands List

Cisco IOS XR interface configuration commands

Cisco IOS XR Interface and Hardware Component Command Reference

Initial system bootup and configuration information for a router using Cisco IOS XR software

Cisco IOS XR Getting Started Guide

Cisco IOS XR AAA services configuration information

Cisco IOS XR System Security Configuration Guide and
Cisco IOS XR System Security Command Reference


Standards

Standards
Title

ANSI T1.617 Annex D

ITU Q.933 Annex A


MIBs

MIBs
MIBs Link

To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml


RFCs

RFCs
Title

RFC 1294

Multiprotocol Interconnect Over Frame Relay

RFC 1315

Management Information Base for Frame Relay DTEs

RFC 1490

Multiprotocol Interconnect Over Frame Relay

RFC 1586

Guidelines for Running OSPF Over Frame Relay Networks

RFC 1604

Definitions of Managed Objects for Frame Relay Service

RFC 2115

Management Information Base for Frame Relay DTEs Using SMIv2

RFC 2390

Inverse Address Resolution Protocol

RFC 2427

Multiprotocol Interconnect Over Frame Relay

RFC 2954

Definitions of Managed Objects for Frame Relay Service


Technical Assistance

Description
Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport