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Table of Contents

SLIP and PPP Configuration Commands

SLIP and PPP Configuration Commands

Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP) define methods of sending IP packets over standard EIA/TIA-232 asynchronous serial lines with minimum line speeds of 1200 baud. This chapter describes the commands used to configure your router to enable SLIP and PPP on asynchronous interfaces.

Using SLIP or PPP encapsulation over asynchronous lines is an inexpensive way of connecting PCs to a network. SLIP and PPP over asynchronous dial-up modems allow a home computer to be connected to a network without the cost of a leased line. Dial-up SLIP and PPP links can also be used for remote sites that need only occasional remote node or backup connectivity. Both public-domain and vendor-supported SLIP and PPP implementations are available for a variety of computer applications.

Use the commands in this chapter to configure SLIP and PPP on your router. For configuration information and examples, refer to the Access Services Configuration Guide.

See the chapter "Making Connections to Network Devices" in the Access Services Configuration Guide for information about SLIP and PPP user-level EXEC connection commands.


Note Some commands previously documented in this chapter have been replaced by new commands. Although these continue to perform their normal functions in the current release, support for these commands will cease in future releases.

async default ip address

The peer default ip address command replaces the async default ip address command.

Refer to the description of the peer default ip address command for more information.

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

async default routing

To enable RIP, OSPF, and IGRP routing protocols on an asynchronous interfaces when using the /routing argument with the ppp and slip EXEC commands, use the async default routing interface command. To disable this function, use the no form of this command.

async default routing
no async default routing

Syntax Description

This command has no arguments or keywords.

Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

For asynchronous interfaces in interactive mode, the async default routing command causes the ppp and slip EXEC commands to be interpreted as though the /route argument had been included in the command. For asynchronous interfaces in dedicated mode, the async default routing command turns on the use of routing protocols on the line. Without the async default routing command, there is no way to enable the use of routing protocols automatically on a dedicated asynchronous interface.

Example

The following example enables the use of routing protocols on asynchronous interface 4. In this example, asynchronous interface 4 is dedicated for asynchronous use.

interface async 4
 ip address 191.191.191.191 255.255.255.0
 async default routing
 async mode dedicated
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

async dynamic routing
async mode dedicated
async mode interactive
ppp
+
slip +

async dynamic address

To specify dynamic asynchronous addressing, use the async dynamic address interface configuration command. To disable dynamic addressing, use the no form of this command.

async dynamic address
no async dynamic address

Syntax Description

This command has no arguments or keywords.

Default

Dynamic addressing is disabled.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

You can control whether addressing is dynamic (the user specifies the address at the EXEC level when making the connection), or whether default addressing is used (the address is forced by the system). If you specify dynamic addressing, the router must be in interactive mode and the user will enter the address at the EXEC level.

It is common to configure an asynchronous interface to have a default address and to allow dynamic addressing. With this configuration, the choice between the default address or a dynamic addressing is made by the user when they enter the slip or ppp EXEC command. If the user enters an address, it is used, and if the user enters the default keyword, the default address is used.

Example

The following example shows dynamic addressing assigned to async interface 6.

Interface ethernet 0
 ip address 10.0.0.1 255.0.0.0
interface async 6
 async dynamic address
Related Command

peer default ip address

async dynamic routing

To allow the use of routing protocols on an interface, use the async dynamic routing interface configuration command. To disable the use of routing protocols, use the no form of this command.

async dynamic routing
no async dynamic routing

Syntax Description

This command has no arguments or keywords.

Default

Dynamic routing is disabled.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

The use of routing protocols is further controlled by the use of the /routing keyword in the slip and ppp EXEC command. Refer to the chapter "Making Connections to Network Devices" in the Access Services Configuration Guide for more information about making SLIP and PPP connections.

Example

The following example shows how to enable asynchronous routing on async interface 6. The ip tcp header-compression passive command enables Van Jacobson TCP header compression and prevents transmission of compressed packets until a compressed packet arrives from the asynchronous link.

interface async 6
 async dynamic routing
 async dynamic address
 async default ip address 10.11.14.2
 ip tcp header-compression passive
 ip unnumbered ethernet 0
Related Commands

async dynamic address
ip tcp header-compression

async mode dedicated

To place a line into dedicated asynchronous mode using SLIP or PPP encapsulation, use the async mode dedicated interface configuration command. To return the line to interactive mode, use the no form of this command.

async mode dedicated
no async mode

Syntax Description

This command has no arguments or keywords.

Default

Asynchronous mode is disabled.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

With dedicated asynchronous network mode, the interface will use either SLIP or PPP encapsulation, depending on which encapsulation method is configured for the interface. An EXEC prompt does not appear, and the router is not available for normal interactive use.

If you configure a line for dedicated mode, you will not be able to use the async dynamic address command, because there is no user prompt.

Example

The following example assigns an IP address to an asynchronous line and places the line into network mode. Setting the stop bits to 1 enhances performance.

interface async 4
async default ip address 172.31.7.51
async mode dedicated
encapsulation slip
line 20 
location Joe's computer
stopbits 1
speed 115200
Related Command

async mode interactive

async mode interactive

To return a line that has been placed into dedicated asynchronous network mode to interactive mode, thereby enabling the slip and ppp EXEC commands, use the async mode interactive interface configuration command. To prevent users from implementing SLIP and PPP at the EXEC level, use the no form of this command.

async mode interactive
no async mode

Syntax Description

This command has no arguments or keywords.

Default

Asynchronous mode is disabled.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Interactive mode enables the slip and ppp EXEC commands. In dedicated mode, there is no user EXEC level. The user does not enter any commands, and a connection is automatically established when the user logs on, according to the configuration.

Example

The following example places async interface 6 into interactive asynchronous mode:

interface async 6
 async default ip address 172.31.7.51
 async mode interactive
 ip unnumbered ethernet 0
Related Command

async mode dedicated

async-bootp

To support the extended BOOTP request specified in RFC 1084, and to specify information that will be sent in response to BOOTP requests, use the async-bootp global configuration command. To clear the list, use the no form of this command.

async-bootp tag [:hostname] data
no async-bootp tag [:hostname] data

Syntax Description
tag Item being requested; expressed as filename, integer, or IP dotted decimal address. See Table 45 for possible values.
:hostname (Optional) This entry applies only to the specified host. The argument can be either an IP address or a logical host name.
data List of IP addresses entered in dotted decimal notation or as logical host names, a number, or a quoted string.


Table 45: Supported Extended BOOTP Requests
Keyword and Argument Pair Use
bootfile Server boot file from which to download the boot program. Use the optional :hostname and data arguments to specify the host or hosts.
subnet-mask mask Dotted decimal address specifying the network and local subnetwork mask (as defined by RFC 950).
time-offset offset A signed 32-bit integer specifying the time offset of the local subnetwork in seconds from Coordinated Universal Time.
gateway address Dotted decimal address specifying the IP addresses of gateways for this subnetwork. A preferred gateway should be listed first.
time-server address Dotted decimal address specifying the IP address of time servers (as defined by RFC 868).
ien116-server address Dotted decimal address specifying the IP address of name servers (as defined by IEN 116).
nbns-server address Dotted decimal address specifying the IP address of Windows NT servers.
dns-server address Dotted decimal address specifying the IP address of Domain Name Servers (as defined by RFC 1034).
log-server address Dotted decimal address specifying the IP address of an MIT-LCS UDP log server.
quote-server address Dotted decimal address specifying the IP address of Quote of the Day servers (as defined in RFC 865).
lpr-server address Dotted decimal address specifying the IP address of Berkeley UNIX Version 4 BSD servers.
impress-server address Dotted decimal address specifying the IP address of Impress network image servers.
rlp-server address Dotted decimal address specifying the IP address of Resource Location Protocol (RLP) servers (as defined in RFC 887).
hostname name Name of the client (which might or might not be domain qualified, depending upon the site).
bootfile-size value Two-octet value specifying the number of 512 octet (byte) blocks in the default boot file.
Default

If no extended BOOTP commands are entered, the software generates a gateway and subnet mask appropriate for the local network.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

Each of the tag keyword-argument pairs is a field that can be filled in and sent in response to BOOTP requests from clients.

BOOTP supports the extended BOOTP requests specified in RFC 1084 and works for both SLIP and PPP encapsulation.

Use the show async bootp EXEC command to list the configured parameters. BOOTP works for both SLIP and PPP.

Examples

The following example specifies different boot files: one for a PC and one for a Macintosh. With this configuration, a BOOTP request from the host on 192.168.31.1 results in a reply listing the boot filename as pcboot. A BOOTP request from the host named mac results in a reply listing the boot filename as macboot.

async-bootp bootfile :192.168.31.1 "pcboot"
async-bootp bootfile :mac "macboot"

The following example specifies a subnet mask of 255.255.0.0:

async-bootp subnet-mask 255.255.0.0

The following example specifies a negative time offset of the local subnetwork of -3600 seconds:

async-bootp time-offset -3600

The following example specifies the IP address of a time server:

async-bootp time-server 192.168.31.1
Related Command

service old-slip-prompts

clear line

To return a line to its idle state, enter the clear line privileged EXEC command at the system prompt.

clear line line-number
Syntax Description
line-number Asynchronous line port number assigned with the interface async command.
Command Mode

Privileged EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Normally, this command returns the line to its conventional function as a terminal line, with the interface left in a "down" state.

Example

The following example shows how to use the clear line command to return serial interface 5 to its idle state:

clear line 5

encapsulation

To configure SLIP or PPP encapsulation as the default on an asynchronous interface, use the encapsulation interface configuration command. To disable encapsulation, use the no form of this command.

encapsulation {slip | ppp}
no encapsulation
{slip | ppp}
Syntax Description
slip Specifies SLIP encapsulation for an interface configured for dedicated asynchronous mode or DDR.
ppp Specifies PPP encapsulation for an interface configured for dedicated asynchronous mode or DDR.
Default

SLIP encapsulation is enabled by default.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

On lines configured for interactive use, encapsulation is selected by the user when they establish a connection with the slip or ppp EXEC command.

IP Control Protocol (IPCP) is the part of PPP that brings up and configures IP links. After devices at both ends of a connection communicate and bring up PPP, they bring up the control protocol for each network protocol that they intend to run over the PPP link such as IP or IPX. If you have problems passing IP packets and the show interface command shows that line is up, use the negotiations command to see if and where the negotiations are failing. You might have different versions of software running, or different versions of PPP, in which case you might need to upgrade your software or turn off PPP option negotiations. All IPCP options as listed in RFC 1332 are supported on asynchronous lines. Only Option 2, TCP/IP header compression, is supported on synchronous interfaces.

PPP echo requests are used as keepalive packets to detect line failure. The no keepalive command can be used to disable echo requests. For more information about the no keepalive command, refer to the chapter "IP Routing Protocols Commands" later in the Networking Protocols Command Reference, Part 1 and the chapter "Configuring IP Routing Protocols" in the Networking Protocols Configuration Guide, Part 1.

In order to use SLIP or PPP, the Cisco IOS software must be configured with an IP routing protocol or with the ip host-routing command. This configuration is done automatically if you are using old-style slip address commands. However, you must configure it manually if you configure SLIP or PPP via the interface async command.


Note Disable software flow control on SLIP and PPP lines.
Example

In the following example, async interface 1 is configured for PPP encapsulation.

walrus# config
Configuring from terminal, memory, or network [terminal]?
Enter configuration commands, one per line. End with CNTL/Z.
tarmac(config)# interface async 1
tarmac(config-if)# encapsulation ppp
Related Command

A dagger (+) indicates that the command is documented outside this chapter.

keepalive +

hold-queue

To limit the size of the IP output queue, use the hold-queue interface configuration command. To return the output queue to the default size, use the no form of this command.

hold-queue packets
no hold-queue

Syntax Description
packets Maximum number of packets. The range of values is 0 through 65535.
Default

10 packets (default for asynchronous interfaces only)

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0. The no hold-queue command first appeared in Cisco IOS Release 11.1.

The default of 10 packets allows the Cisco IOS software to queue a number of back-to-back routing updates. This is the default for asynchronous interfaces only; other media types have different defaults.

The hold queue stores packets received from the network that are waiting to be sent to the client. It is recommended that the queue size not exceed ten packets on asynchronous interfaces. For most other interfaces, queue length should not exceed 100.

Example

The following example changes the packet queue length of a line to five packets:

interface async 2
 async default ip address 172.31.7.5
 hold-queue 5

interface

To specify the interface you want to configure, use the interface global configuration command. To clear the interface configuration, use the no form of this command.

interface type number
no interface

Syntax Description
type Interface type.
number Interface number. See Table 46 for a list of interface numbers by router model.


Table 46: Interface Numbers by Access Server Model
Access Server Model Interface Number
Cisco 1001 1 to 2
Cisco 2509 or 2510 1 to 8
Cisco 2511 or 2512 1 to 16
AS5100 1 to 48
Default

No interface is specified by default; you must specify an interface to configure it.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.0.

Example

The following example specifies async interface 1:

interface async 1

ip access-group

To configure an access list to be used for packets transmitted to and from the asynchronous host, use the ip access-group interface configuration command. To disable control over packets transmitted to or from an asynchronous host, use the no form of this command.

ip access-group access-list-number {in | out}
no ip access-group access-list-number

Syntax Description
access-list-number Assigned IP access list number.
in Defines access control on packets transmitted from the asynchronous host.
out Defines access control on packets being sent to the asynchronous host.
Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

With this command in effect, the IP destination address of each packet is run through the access list for acceptability and dropped or passed.

Example

The following example assumes that users are restricted to certain servers designated as SLIP or PPP servers, but that normal terminal users can access anything on the local network:

! access list for normal connections
access-list 1 permit 172.16.0.0 0.0.255.255
!
! access list for SLIP packets.
access-list 2 permit 172.16.42.55
access-list 2 permit 172.16.111.1
access-list 2 permit 172.16.55.99
!
! Specify the access list
interface async 6
async dynamic address
ip access-group 1 out
ip access-group 2 in

ip address

To set IP addresses for an interface, use the ip address interface configuration command. To remove the specified addresses, use the no form of this command.

ip address address mask [secondary]
no ip address address mask [secondary]

Syntax Description
address IP address.
mask Network mask for the associated IP network.
secondary (Optional) Specifies additional IP addresses.
Default

No IP addresses are specified.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

The subnet mask must be the same for all interfaces connected to subnets of the same network. Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) Mask Request message. The Cisco IOS software responds to this request with an ICMP Mask Reply message.

You can disable IP processing on a particular interface by removing its IP address with the no ip address interface configuration command. If the router detects another host using one of its IP addresses, it will print an error message on the console.

Example

In the example that follows, 172.16.1.27 is the primary address and 192.168.7.17 and 192.168.8.17 are secondary addresses for async interface 1:

interface async 1
ip address 172.16.1.27 255.255.255.0
ip address 192.168.7.17 255.255.255.0 secondary
ip address 192.168.8.17 255.255.255.0 secondary

ip mtu

To specify the size of the largest Internet packet, use the ip mtu interface configuration command. To return to the default MTU size of 1500 bytes, use the no form of this command.

ip mtu bytes
no ip mtu

Syntax Description
bytes Maximum number of bytes. The range of values is 64 to 1000000.
Default

1500 bytes

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Example

The following example sets the packet MTU size to 200 bytes:

interface async 5
 async default ip address 172.31.7.5
 ip mtu 200

ip tcp header-compression

To configure Van Jacobson TCP header compression on the asynchronous link, use the ip tcp header-compression line configuration command. To disable header compression, use the no form of this command.

ip tcp header-compression [on | off | passive]
no ip tcp header-compression

Syntax Description
on (Optional) Turns header compression on.
off (Optional) Turns header compression off.
passive (Optional) On SLIP lines, prevents transmission of compressed packets until a compressed packet arrives from the asynchronous link, unless a user specifies SLIP on the command line. For PPP, this option functions the same as the on option.
Default

Header compression is on.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Header compression data areas are initialized to handle up to 16 simultaneous TCP connections. Currently, you cannot change this number. You can only turn header compression on or off or use the passive keyword.

On lines configured for PPP encapsulation, the keywords passive and on cause the same behavior because, before attempting header compression, PPP automatically negotiates whether it is available at each end of the connection.

There are two ways to implement header compression when the line is configured for ip tcp header-compression passive:

If a line is configured for passive header compression and you use the slip or ppp EXEC command to enter asynchronous mode, you will see that the interface is set to match compression status used by the host at the other end of the asynchronous line.

Server> slip 10.0.0.1
Password:
Entering SLIP mode.
Interface IP address is 10.0.0.1, MTU is 1500 bytes
Header compression will match your system.

The message "Header compression will match your system" indicates that the interface is set to match the compression status used by the host at the other end of the asynchronous line. If the line was configured to have header compression on, this line would read "Header compression is On." Refer to the chapter "Making Connections to Network Devices" in the Access Services Configuration Guide for more information about making SLIP and PPP connections.

Example

The following example illustrates how to enable Van Jacobson TCP header compression. The passive keyword prevents transmission of compressed packets until a compressed packet arrives from the IP link. Notice that asynchronous routing and dynamic addressing are also enabled.

interface async 6
 async dynamic routing
 async dynamic address
 ip tcp header-compression passive
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

ppp +
slip +
slip default +
slip /compressed +



ip unnumbered

To conserve network resources, use the ip unnumbered line configuration command. To disable unnumbered interfaces, use the no form of this command.

ip unnumbered type number
no ip unnumbered

Syntax Description
type Interface type.
number Interface number.
Default

Disabled

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

You must use either the ip address or ip unnumbered command to provide the local address for an interface.

Unnumbered interfaces do not have an address. Network resources are conserved because fewer network numbers are used and routing tables are smaller.

Whenever the unnumbered interface generates a packet (for example, a routing update), it uses the address of the specified interface as the source address of the IP packet. It also uses the address of the specified interface to determine which routing processes are sending updates over the unnumbered interface. Restrictions include the following:

Example

The following example shows how to configure async interface 6 as unnumbered:

interface async 6
 ip unnumbered ethernet 0
Related Command

ip address

ipx compression cipx

To enable compression of IPX packet headers in a PPP session, use the ipx compression cipx interface configuration command. To disable compression of IPX packet headers in a PPP session, use the no form of this command.

ipx compression cipx number-of-slots
no ipx compression cipx

Syntax Description
number-of-slots Number of stored IPX headers allowed. The range is from 10 to 256. The default is 16.

A slot is similar to a table entry for a complete IPX header. When a packet is received, the receiver stores the complete IPX header in a slot and tells the destination which slot it used. As subsequent CIPX packets are sent, the receiver uses the slot number field to determine which complete IPX header to associate with the CIPX packet before passing the packet up to IPX.

Default

No compression of IPX packets during a PPP session.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

This interface configuration command enables IPX header compression on PPP links.

Example

The following example enables IPX header compression for PPP:

Router(config-if)# encapsulation ppp
Router(config-if)# ipx compression enable 128
Related Command

show ipx compression

ipx ppp-client

To enable a non-routing IPX client to connect to an asynchronous interface, the interface must be associated with a loopback interface configured to run IPX. To permit such connections, use the ipx ppp-client interface configuration command. To disable a non-routing IPX client, use the no form of this command.

ipx ppp-client loopback number
no vty-async

Syntax Description
loopback Loopback interface configured with a unique IPX network number.
number Number of the loopback interface.
Default

IPX client connections are not permitted over PPP.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

This command enables IPX clients to log into the router from a device running a virtual terminal protocol, then issue the PPP command at the EXEC prompt to connect to a remote device.

You must first configure a loopback interface with a unique IPX network number. The loopback interface is then assigned to an asynchronous interface, which permits IPX clients to connect to the asynchronous interface.

Example

The following example shows the process of configuring IPX to run over PPP on asynchronous interface 3:

Router(config)# ipx routing 0000.0c07.b509
Router(config)# interface loopback0
Router(config-if)# no ip address
Router(config-if)# ipx network 544
Router(config-if)# ipx sap-interval 2000
Router(config-if)# exit
Router(config)# interface ethernet0
Router(config-if)# ip address 172.21.14.64
Router(config-if)# ipx network AC150E00
Router(config-if)# ipx encapsulation SAP
Router(config-if)# exit
Router(config)# interface async 3
Router(config-if)# ip unnumbered ethernet0 
Router(config-if)# encapsulation ppp
Router(config-if)# async mode interactive 
Router(config-if)# async default ip address 172.18.1.128
Router(config-if)# ipx ppp-client loopback0
Router(config-if)# ipx sap-interval 0 
Related Commands

interface loopback
ipx network

netbios nbf

To enable the NetBIOS Frames Protocol (NBF) on an interface, use the netbios nbf interface configuration command. To disable NetBIOS Frames Protocol support on an interface, use the no form of this command.

netbios nbf
no netbios nbf

Syntax Description

This command has no arguments or keywords.

Default

Disabled.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

Example

The following example enables NetBIOS Frames Protocol on asynchronous interface 1 (connected to remote access client using a NetBEUI application) and Ethernet interface 0 (connected to the remote router):

interface async 1
 netbios nbf
interface ethernet 0
 netbios nbf
Related Commands

A dagger (+) indicates that the command is documented outside this publication.

netbios name-cache +
show netbios cache
show nbf sessions

peer default ip address

Use the peer default ip address interface configuration command to specify an IP address, an address from a specific IP address pool, or an address from the DHCP mechanism to be returned to a remote peer connecting to this interface. This command sets the address used on the remote (PC) side. Use the no form of this command to disable a prior peer IP address pooling configuration on an interface.

To remove the default address from your configuration, use the no form of this command.

peer default ip address {ip-address | dhcp | pool [poolname]}
no peer default ip address

Syntax Description
ip-address Specific IP address to be assigned to a remote peer dialing in to this interface. To prevent the assignment of duplicate IP addresses on two or more interfaces, this form of the command cannot be applied to a dialer rotary group nor to an ISDN interface.
dhcp Retrieve an IP address from the DHCP server.
pool Use the Global Default Mechanism as defined by the ip address-pool command unless the optional poolname is supplied.
poolname (Optional) Name of a local address pool created using the ip local pool command. The router retrieves an address from this pool regardless of the Global Default Mechanism setting.
Default

pool

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.0.

This command applies to point-to-point interfaces that support the PPP or SLIP encapsulation.


Note This command replaces the async default ip address command.

This command allows an administrator to configure all possible address pooling mechanisms on a interface-by-interface basis. The peer default ip address command can be used to override the Global Default Mechanism defined by the ip address-pool command on an interface-by-interface basis.

For all interfaces not configured with a peer default IP address mechanism (equivalent to selecting the peer default ip address pool command), the router uses the Global Default Mechanism that is defined by the ip address-pool command.

If you select the peer default ip address pool poolname command, then the router uses the locally configured pool on this interface and does not follow the Global Default Mechanism.

If you select the peer default ip address ip-address form of this command, the specified IP address is assigned to any peer connecting to this interface and any Global Default Mechanism is overridden for this interface.

If you select the peer default ip address dhcp form of this command, the DHCP proxy-client mechanism is used by default on this interface and any Global Default Mechanism is overridden for this interface.

Example

The following example specifies address 192.31.7.51 for async interface 6:

line 20
 speed 115200
interface async 6
 peer default ip address 192.31.7.51
Related Command

async dynamic address

ppp callback

To enable a PPP client to dial into an asynchronous interface and request a callback, use the ppp callback interface configuration command.

ppp callback {accept | initiate}
Syntax Description
accept Accept callback requests from RFC1570-compliant PPP clients on the interface.
initiate Initiate a callback to non-RFC1570-compliant PPP clients dialing in an asynchronous interface.
Default

Callback requests are not accepted on asynchronous interfaces.

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.0.

This command enables the Cisco IOS software to accept callback requests entering asynchronous interfaces configured for PPP callback. PPP callback can only be initiated if the interface is configured for authentication using CHAP or PAP.

Examples

The following example accepts a callback request from an RFC-compliant PPP client:

ppp callback accept

The following example accepts a callback request from a non-RFC-compliant PPP client:

ppp callback initiate
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

arap callback +
autoselect ppp
callback-forced-wait
+
ppp authentication
username
+

service old-slip-prompts

To provide backward compatibility for client software scripts expecting SLIP and PPP dialogs to be formatted with software release 9.1 or earlier, use the service old-slip-prompts global configuration command. Use the no form of this command to disable this function.

service old-slip-prompts
no service old-slip-prompts

Syntax Description

This command has no arguments or keywords.

Default

The prompts and information transmitted by SLIP and PPP are formatted with the current release of Cisco IOS.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

Example

The following example shows the output of a SLIP command after service old-slip-prompts is enabled.

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# service old-slip-prompts
Router(config)# exit
Router# slip
IP address or hostname: 2.2.2.2
Entering SLIP mode.
Your IP address is 2.2.2.2. MTU is 1500 bytes

show async bootp

To display the parameters that have been configured for extended BOOTP requests, use the show async bootp privileged EXEC command.

show async bootp
Syntax Description

This command has no arguments or keywords.

Command Mode

Privileged EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Sample Display

The following is sample output from the show async bootp command.

sloth# show async bootp
The following extended data will be sent in BOOTP responses:
bootfile (for address 192.168.31.1) "pcboot"
bootfile (for address 172.16.1.110) "dirtboot"
subnet-mask 255.255.0.0
time-offset -3600
time-server 192.168.31.1

Table 47 describes significant fields shown in the display.


Table 47: Show Async BOOTP Field Descriptions
Field Description
bootfile... "pcboot" Indicates that the boot file for address 192.168.31.1 is named pcboot.
subnet-mask 255.255.0.0 Specifies the subnet mask.
time-offset -3600 Indicates that the local time is one hour (3600 seconds) earlier than Coordinated Universal Time (UTC).
time-server 192.168.31.1 Indicates the address of the time server for the network.

show async status

To display the status of activity on all lines configured for asynchronous support, use the show async status privileged EXEC command.

show async status
Syntax Description

This command has no arguments or keywords.

Command Mode

Privileged EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

The display resulting from this command shows all asynchronous sessions, whether they are using SLIP or PPP encapsulation.

Sample Display

The following is sample output from the show async status command:

Router# show async status
Async protocol statistics:
  Rcvd: 5448 packets, 7682760 bytes
        1 format errors, 0 checksum errors, 0 overrun, 0 no buffer
  Sent: 5455 packets, 7682676 bytes, 0 dropped
 Tty           Local           Remote Qd InPack OutPac Inerr  Drops  MTU Qsz
   1     192.168.7.84         Dynamic  0      0      0     0      0 1500  10
*  3     192.168.7.98            None  0   5448   5455     1      0 1500  10

Table 48 describes significant fields shown in the display.


Table 48: Asynchronous Statistics Display Field Descriptions
Field Description
Rcvd Statistics on packets received.
5448 packets Packets received.
7682760 bytes Total number of bytes.
1 format errors Spurious characters received when a packet start delimiter is expected.
0 checksum errors Count of checksum errors.
0 overrun Number of giants received.
0 no buffer Number of packets received when no buffer was available.
Sent Statistics on packets sent.
5455 packets Packets sent.
7682676 bytes Total number of bytes.
0 dropped Number of packets dropped.
Tty Line number.
* Line currently in use.
Local Local IP address on the link.
Remote Remote IP address on the link; "Dynamic" indicates that a remote address is allowed but has not been specified; "None" indicates that no remote address is assigned or being used.
Qd Number of packets on hold queue (Qsz is the maximum).
InPack Number of packets received.
OutPac Number of packets sent.
Inerr Number of total input errors; sum of format errors, checksum errors, overruns and no buffers.
Drops Number of packets received that would not fit on the hold queue.
MTU Current maximum transmission unit size.
Qsz Current output hold queue size.

show ipx compression

To show the current status and statistics of IPX header compression during PPP sessions, use the show ipx compression EXEC command.

show ipx compression detail int-spec
Syntax Description
detail Shows detailed link-state database information for NLSP.
int-spec Interface type, as listed in Table 49.


Table 49: Interface Specifications for Show IPX Compression Command
Keyword Description
Async Asynchronous interface.
Ethernet Ethernet IEEE 802.3 interface.
Null Null interface.
Serial WAN serial interface.
Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

Related Commands

A dagger (+) indicates that the command is documented outside this publication.

ipx compression cipx
show ipx interface
+

show line

Use the show line privileged EXEC command to display connection status for a line running in asynchronous mode.

show line [line-number]
Syntax Description
line-number (Optional) Particular line about which information will be displayed. If you do not specify a line number, information about all lines is displayed.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Sample Display

The following is sample output from the show line command:

mosey> show line

 Tty Typ    Tx/Rx    A Modem  Roty AccO AccI  Uses    Noise   Overruns
*  0 CTY             -    -      -    -    -     0        0        0/0
A  1 TTY  9600/9600  -    -      -    -    1     0        0        0/0
   2 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   3 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   4 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   5 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   6 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   7 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   8 TTY  9600/9600  -    -      -    -    -     0        0        0/0
   9 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  10 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  11 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  12 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  13 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  14 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  15 TTY  9600/9600  -    -      -    -    -     0        0        0/0
  16 TTY  9600/9600  -    -      -    -    -     0        0        0/0
* 17 VTY  9600/9600  -    -      -    -    -    18        0        0/0

Table 50 describes significant fields shown in the display.


Table 50: Show Line Field Descriptions
Task Description
(first character in line) The field preceding the number in the TTY field can be blank or contain one of the following characters:
*--The line is currently active, running a terminal-oriented protocol.
A--The line is currently active in asynchronous mode.
I--The line is free and can be used for asynchronous modes because it is
      configured for async mode interactive.

Tty

Indicates the absolute line number of the specified line.
Typ Type of line. Possible values follow:

  • CTY--Console

  • AUX--Auxiliary port

  • TTY--Asynchronous terminal port

  • VTY--Virtual terminal

  • LPT--Parallel printer

Tx/Rx

Transmit rate of the line (baud)/receive rate of the line (baud).
A Indicates whether or not autobaud has been configured for the line. A value of F indicates that autobaud has been configured; a hyphen (-) indicates that it has not been configured for the line.
Modem Types of modem signal that has been configured for the line. Possible values include:

  • callin

  • callout

  • cts-req

  • DTR-Act

  • inout

  • RIisCD

Roty

Rotary Group configured for this line.
AccO Output access list number configured for the specified line.
AccI Input access list number configured for the specified line.
Uses Number of connections established to or from this line since the system was restarted.
Noise Number of times noise has been detected on the line since the system restarted.
Overruns Hardware (UART) overruns/software buffer overflows, both defined as the number of overruns or overflows that have occurred on the specified line since the system was restarted. Hardware overruns are buffer overruns; the UART chip has received bits from the software faster than it can process them. A software overflow occurs when the software has received bits from the hardware faster than it can process them.

The following is sample output from the show line command when a line is specified:

Router> show line 1
 Tty Typ    Tx/Rx    A Modem  Roty AccO AccI  Uses    Noise Overruns
   1 TTY  9600/9600  -    -      -    -   10     0        0        0
Line 1, Location: "charnel console", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600, no parity, 2 stopbits, 8 databits
Status: Ready, Hardware XON/XOFF
Capabilities: none
Modem state: Ready
Special Chars: Escape  Hold  Stop  Start  Disconnect  Activation
                ^^x    none   -     -       none
Timeouts:      Idle EXEC    Idle Session   Modem Answer  Session   Dispatch
               0:10:00        never         0:00:15      not imp   not set
Session limit is not set.
Allowed transports are telnet lat rlogin.  Preferred is lat
No output characters are padded
Characters causing immediate data dispatching:
   Char    ASCII
Group codes:    0
Related Commands

async dynamic address
async dynamic routing
ip tcp header-compression


show nbf cache

Use the show nbf cache user level EXEC command to display NetBIOS name cache contents.

show nbf cache
Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

Sample Display

The following is sample output from the show line command:

scarlet> show nbf cache 
 HW Addr           Name        How     Idle   NetBIOS Packet Savings
1000.5a89.449a    IKBA         E0      6      0
0000.0000.0000    NANOO        async1  21     0

Table 51 describes significant fields shown in the display.


Table 51: Show nbf cache Field Descriptions
Field Description
HW Addr MAC address mapped to the NetBIOS name in this entry.
Name NetBIOS name mapped to the MAC address in this entry.
How Interface through which this information was learned.
Idle Period of time (in seconds) since this entry was last accessed. A hyphen in this column indicates a static entry in the NetBIOS name cache.
NetBIOS Packet Savings Number of packets to which local replies were made (thus preventing transmission of these packets over the network).
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

netbios access-list +
netbios input-access-filter +
netbios output-access-filter +
netbios name-cache +
netbios nbf
show nbf sessions

show nbf sessions

Use the show nbf sessions user level EXEC command to view NetBEUI connection information.

show nbf sessions
Syntax Description

This command has no arguments or keywords.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.1.

Sample Display

The following is sample output from the show nbf sessions command:

lefevre> show nbf session
Async6 NetBIOS Session Table: 
Srcnum   Destnum  Dest-Interface DestMAC
8        6         Ethernet0 00aa.005b.c17b
NetBIOS Global Session Table: 
Srcnum   Destnum   Dest-Interface DestMAC  Src-Interface SrcMac(I)
6        8         Async7 0000.0000.0000  Ethernet0 00aa.005b.c17b(95)
ADD_[GROUP]NAME_QUERY queuesize=0
STATUS_QUERY queuesize=0
STATUS_RESPONSE queuesize=0
NAME_QUERY queuesize=0
NAME_RECOGNIZED queuesize=0
SESSION_INITIALIZE queuesize=0
SESSION_INITIALIZE (pending) queuesize=0

Table 52 describes significant fields shown in the display.


Table 52: Show nbf sessions Field Descriptions
Field Description
Interface NetBIOS Session Table: Summarizes Async/ISDN interface NetBIOS connection information.
Srcnum, Destnum Source and destination connection numbers.
Dest-Interface, DestMAC Destination interface and MAC address.
Global NetBIOS Session Table: Summarizes LAN NetBIOS connection information.
Dest-Interface DestMAC Destination interface (Async7 in this case) and MAC address (0000.0000.0000 in this case).
Src-Interface SrcMac Source interface (Ethernet0 in this case) and MAC address (00aa.005b.c17b(95) in this case).
NetBIOS Datagram Queue Summary Summarizes NetBIOS pending datagram queues.
ADD_[GROUP]NAME_QUERY Add Group Name Query packets.
STATUS_QUERY Status query packets.
STATUS_RESPONSE Status Response packets.
NAME_QUERY Name Query packets.
NAME_RECOGNIZED Name Recognized packets.
SESSION_INITIALIZE (pending) NetBios session Initialize packets.
Related Commands

A dagger (+) indicates that the command is documented outside this publication.

netbios access-list +
netbios input-access-filter +
netbios output-access-filter
+
netbios name-cache
+
netbios nbf
show nbf cache

vty-async

To configure all virtual terminal lines on a router to support asynchronous protocol features, use the vty-async global configuration command. Use the no form of this command to disable asynchronous protocol features on virtual terminal lines.

vty-async
no vty-async

Syntax Description

This command has no arguments or keywords.

Default

Asynchronous protocol features are not enabled by default on virtual terminal lines.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

The vty-async command extends asynchronous protocol features from physical asynchronous interfaces to virtual terminal lines. Normally, SLIP and PPP can function only on asynchronous interfaces, not on virtual terminal lines. However, extending asynchronous functionality to virtual terminal lines permits you to run SLIP and PPP on these virtual asynchronous interfaces. One practical benefit is the ability to tunnel SLIP and PPP over X.25 PAD, thus extending remote node capability into the X.25 area. You can also tunnel SLIP and PPP over Telnet or LAT on virtual terminal lines. To tunnel SLIP and PPP over X.25, LAT, or Telnet, you use the protocol translation feature in the Cisco IOS software.

To tunnel SLIP or PPP inside X.25, LAT, or Telnet, you can use two-step protocol translation or one-step protocol translation, as follows:

Example

The following example enables asynchronous protocol features on virtual terminal lines:

vty-async
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

ppp +
slip +
translate +

vty-async dynamic-routing

To enable dynamic routing on all virtual asynchronous interfaces, use the vty-async dynamic-routing global configuration command. Use the no form of this command to disable asynchronous protocol features on virtual terminal lines and, therefore, disable routing on virtual terminal lines.

vty-async dynamic-routing
no vty-async

Syntax Description

This command has no arguments or keywords.

Default

Dynamic routing is not enabled on virtual asynchronous interfaces.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

This feature enables IP routing on virtual asynchronous interfaces. When you issue this command and a user later makes a connection to another host using SLIP or PPP, the user must specify /routing on the SLIP or PPP command line.

If you had not previously entered the vty-async command, the vty-async dynamic-routing command creates virtual asynchronous interfaces, then enables dynamic routing on them.

Example

The following example enables dynamic routing on virtual asynchronous interfaces:

vty-async dynamic-routing 
Related Command

async dynamic routing

vty-async header-compression

To compress the headers of all TCP packets on virtual asynchronous interfaces, use the vty-async header-compression global configuration command. Use the no form of this command to disable virtual asynchronous interfaces and header compression.

vty-async header-compression [passive]
no vty-async

Syntax Description
passive (Optional) Specifies that outgoing packets to be compressed only if TCP incoming packets on the same virtual asynchronous interface are compressed. For SLIP, if you do not specify this option, the Cisco IOS software will compress all traffic. The default is no compression. For PPP, the Cisco IOS software always negotiates header compression.
Default

Header compression is not enabled on virtual asynchronous interfaces.

Command Mode

Global Configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

This feature compresses the headers on TCP/IP packets on virtual asynchronous connections to reduce the size of the packets and to increase performance.This feature only compresses the TCP header, so it has no effect on UDP packets or other protocol headers. The TCP header compression technique, described fully in RFC 1144, is supported on virtual asynchronous interfaces using SLIP or PPP encapsulation. You must enable compression on both ends of a connection.

Example

The following example compresses outgoing TCP packets on virtual asynchronous interfaces only if incoming TCP packets are compressed:

vty-async header-compression passive
Related Command

async dynamic routing

vty-async ipx ppp-client loopback

To enable IPX-PPP on virtual terminal (VTY) lines, use the vty-async ipx ppp-client loopback global configuration command. Use the no form of this command to disable IPX-PPP sessions on VTYs.

vty-async ipx ppp-client loopback number
no vty-async

Syntax Description
number Number of the loopback interface configured for IPX to which the VTY lines are assigned.
Default

IPX over PPP is not enabled on VTY lines.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 11.0.

This command enables users to log into the router from a device running a virtual terminal protocol, then issue the PPP command at the EXEC prompt to connect to a remote device.

A loopback interface must already have been defined and an IPX network number must have been assigned to the loopback interface before the vty-async ipx ppp-client loopback command will permit IPX-PPP on VTY lines.

Example

The following example enables IPX over PPP on VTY lines:

Router(config)# ipx routing ramana
Router(config)# interface loopback0
Router(config-if)# ipx network 12345
Router(config-if)# exit
Router(config)# vty-async ipx ppp-client loopback0
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

interface loopback +
ipx network
+

vty-async keepalive

To change the frequency of keepalive packets on all virtual asynchronous interfaces, use the vty-async keepalive global configuration command. Use the no vty-async command to disable asynchronous protocol features on virtual terminal lines, or the vty-async keepalive 0 command to disable keepalive packets on virtual terminal lines.

vty-async keepalive seconds
no vty-async
vty-async keepalive 0

Syntax Description
seconds The frequency, in seconds, with which the Cisco IOS software sends keepalive messages to the other end of a virtual asynchronous interface. To disable keepalive packets, use a value of 0. The active keepalive interval is 1 through 32767 seconds.
Default

10 seconds

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

Use this command to change the frequency of keepalive updates on virtual asynchronous interfaces from the default of 10, or to disable keepalive updates. If you do not change from the default of 10, the keepalive interval does not appear in show running-config or show translate output.

A connection is declared down after three update intervals have passed without receiving a keepalive packet.

Examples

In the following example, the keepalive interval is set to 30 seconds.

vty-async keepalive 30

In the following example, the keepalive interval is set to 0 (off), and the sample output for show running-config is shown.

vty-async keepalive 0
Router# show running-config
no vty-async keepalive
Related Command

A dagger (+) indicates that the command is documented outside this chapter.

keepalive +

vty-async mtu

To set the maximum transmission unit (MTU) size on virtual asynchronous interfaces, use the vty-async mtu global configuration command. Use the no form of this command to disable asynchronous protocol features on virtual terminal lines.

vty-async mtu bytes
no vty-async

Syntax Description
bytes MTU size of IP packets that the virtual asynchronous interface can support. The default MTU is 1500 bytes, the minimum MTU is 64 bytes, and the maximum is 1,000,000 bytes.
Default

1500 bytes

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

Use this command to modify the maximum transmission unit (MTU) for packets on a virtual asynchronous interfaces. You might want to change to a smaller MTU size for IP packets transmitted on a virtual terminal line configured for asynchronous functions for any of the following reasons:

Do not change the MTU size unless the SLIP or PPP implementation running on the host at the other end of the virtual asynchronous interface supports reassembly of IP fragments. Because each fragment occupies a spot in the output queue, it might also be necessary to increase the size of the SLIP or PPP hold queue if your MTU size is such that you might have a high amount of packet fragments in the output queue.

Example

The following example sets the MTU for IP packets to 256 bytes:

vty-async mtu 256
Related Command

A dagger (+) indicates that the command is documented outside this chapter.

mtu +

vty-async ppp authentication

To enable PPP authentication on virtual asynchronous interfaces, use the vty-async ppp authentication {chap | pap} global configuration command. Use the no vty-async command to globally disable asynchronous protocol features on virtual terminal lines, or the no vty-async ppp authentication {chap | pap} command to disable PPP authentication.

vty-async ppp authentication {chap | pap}
no vty-async
no
vty-async ppp authentication {chap | pap}

Syntax Description
chap Enable CHAP on all virtual asynchronous interfaces.
pap Enable PAP on all virtual asynchronous interfaces.
Default

No CHAP or PAP authentication for PPP.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

This command configures the virtual asynchronous interface to either authenticate CHAP or PAP while running PPP. Once you have enabled CHAP or PAP, the local router requires a password from remote devices. If the remote device does not support CHAP or PAP, no traffic will be passed to that device.

Example

The following example enables CHAP authentication for PPP sessions on virtual asynchronous interfaces:

vty-async authentication ppp chap
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

ppp authentication chap +
ppp authentication pap
+
ppp use-tacacs
+
vty-async ppp use-tacacs

vty-async ppp use-tacacs

To enable TACACS authentication for PPP on virtual asynchronous interfaces, use the vty-async ppp global configuration command. Use the no form of this command to disable virtual asynchronous interfaces, or the no vty-async use-tacacs command to disable TACACS authentication on virtual asynchronous interfaces.

vty-async ppp use-tacacs
no vty-async
no
vty-async ppp use-tacacs

Syntax Description

This command has no arguments or keywords.

Default

TACACS for PPP is disabled.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.3.

This command requires the extended TACACS server.

Once you have enabled TACACS, the local router requires a password from remote devices.

This feature is useful when integrating TACACS with other authentication systems that require a clear-text version of a user's password. Such systems include one-time password systems and token card systems.

If the username and password are contained in the CHAP password, then the CHAP secret is not used by the router. Because most PPP clients require that a secret be specified, you can use any arbitrary string; the Cisco IOS software ignores it.

You cannot enable TACACS authentication for SLIP on asynchronous or virtual asynchronous interfaces.

Example

The example enables TACACS authentication for PPP sessions:

vty-async ppp use-tacacs
Related Commands

A dagger (+) indicates that the command is documented outside this chapter.

ppp use-tacacs +
vty-async ppp authentication

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