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Cisco IOS Interface Command Reference, Release 12.1
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About the Cisco IOS Software Documentation
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Using Cisco IOS Software
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Interface Commands - Introduction
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Interface Commands (access-list - cut-through)
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Interface Commands (dce-terminal-timing enable - interface)
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Interface Commands (interface fastethernet - loopback line)
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Interface Commands (loopback remote - service-module t1 remote-loopback)
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Interface Commands (service-module t1 timeslots - show hub)
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Interface Commands (show interfaces - show interfaces vg-anylan)
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Interface Commands (show pas caim - tx-queue-limit)
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Index
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Table Of Contents
half-duplex controlled-carrier
dce-terminal-timing enable
To prevent phase shifting of the data with respect to the clock when running the line at high speeds and long distances, use the dce-terminal-timing enable interface configuration command. If SCTE terminal timing is not available from the DTE, use no form of this command, which causes the DCE to use its own clock instead of SCTE from the DTE.
dce-terminal-timing enable
no dce-terminal-timing enable
Syntax Description
This command has no arguments or keywords.
Defaults
DCE uses its own clock.
Command Modes
Interface configuration
Command History
Usage Guidelines
On the Cisco 4000 router, you can specify the serial Network Interface Module timing signal configuration. When the board is operating as a DCE and the DTE provides terminal timing (SCTE or TT), the dce-terminal-timing enable command causes the DCE to use SCTE from the DTE.
Examples
The following example prevents phase shifting of the data with respect to the clock:
Router(config)# interface serial 0Router(config-if)# dce-terminal-timing enabledefault (interface)
To reset the configuration of an interface back to its default values, use the default command in global configuration mode.
default interface-type interface-number
Syntax Description
Defaults
Existing interface configuration values are not reset.
Command Modes
Global configuration
Command History
Usage Guidelines
The default command is a general-purpose command that is not limited to interfaces; it resets defaults based on the command name that follows it. Use the default (interface) command when you need to remove any configuration for a specified interface and reset the interface to its default values.
Examples
The following example demonstrates how to reset serial interface 0 to its default values.
Router(config)# default serial 0Related Commands
delay
To set a delay value for an interface, use the delay interface configuration command. To restore the default delay value, use the no form of this command.
delay tens-of-microseconds
no delay
Syntax Description
tens-of-microseconds
Integer that specifies the delay in tens of microseconds for an interface or network segment. To see the default delay, use the show interfaces command.
Defaults
Default delay values may be displayed with the EXEC command show interfaces.
Command Modes
Interface configuration
Command History
Examples
The following example sets a 30,000-microsecond delay on serial interface 3:
Router(config)# interface serial 3Router(config-if)# delay 3000Related Commands
show interfaces
Displays the statistical information specific to a serial interface.
description (controller)
To add a description to an E1 or T1 controller or the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the description controller configuration command. To remove the description, use the no form of this command.
description string
no description
Syntax Description
string
Comment or a description (up to 80 characters) to help you remember what is attached to the interface.
Defaults
No description is added.
Command Modes
Controller configuration
Command History
10.3
This command was introduced.
11.3
This command was modified to include the CT3IP controller.
Usage Guidelines
The description command is meant solely as a comment to be put in the configuration to help you remember what certain controllers are used for. The description affects the CT3IP and MIP interfaces only and appears in the output of the show controller t3, show controller e1, show controller t1, and more system:running-config EXEC commands.
Examples
The following example describes a 3174 controller:
Router(config)# controller t1Router(config-controller)# description 3174 Controller for test labRelated Commands
down-when-looped
To configure an interface to inform the system it is down when loopback is detected, use the down-when-looped interface configuration command.
down-when-looped
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is valid for HDLC or PPP encapsulation on serial and HSSI interfaces.
There is not a no form of this command.
Backup Interfaces
When an interface has a backup interface configured, it is often desirable that the backup interface be enabled when the primary interface is either down or in loopback. By default, the backup is only enabled if the primary interface is down. By using the down-when-looped command, the backup interface will also be enabled if the primary interface is in loopback.
Testing an Interface with the Loopback Command
If testing an interface with the loopback command, or by placing the DCE into loopback, down-when-looped should not be configured; otherwise, packets will not be transmitted out the interface that is being tested.
Examples
The following example configures interface serial 0 for HDLC encapsulation. It is then configured to let the system know that it is down when in loopback mode.
Router(config)# interface serial0Router(config-if)# encapsulation hdlcRouter(config-if)# down-when-loopedRelated Commands
backup interface
Configures an interface as a secondary or dial backup interface.
Diagnoses equipment malfunctions between an interface and a device.
dsu bandwidth
To specify the maximum allowable bandwidth used by the PA-E3 port adapter and PA-T3 port adapter, use the dsu bandwidth interface configuration command. To return to the default bandwidth, use the no form of this command.
dsu bandwidth kbps
no dsu bandwidth
Syntax Description
kbps
Maximum bandwidth in the range of 22 kbps to 44736 kbps. The default values are:
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34010 kbps for PA-E3
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Defaults
34010 kbps for PA-E3
44736 kbps for PA-T3
Command Modes
Interface configuration
Command History
Usage Guidelines
The local interface configuration must match the remote interface configuration. For example, if you reduce the maximum bandwidth to 16000 on the local port, you must also do the same on the remote port.
The dsu bandwidth command reduces the bandwidth by padding the E3 and T3 frame.
To verify the data service unit (DSU) bandwidth configured on the interface, use the show controllers serial EXEC command.
Examples
The following example sets the DSU bandwidth to 16000 kbps on interface 1/0/0:
Router(config)# interface serial 1/0/0Router(config-if)# dsu bandwidth 16000Related Commands
dsu mode
To specify the interoperability mode used by a PA-E3 port adapter or PA-T3 port adapter, use the dsu mode interface configuration command. To return to the default mode, use the no form of this command.
dsu mode {0 | 1 | 2}
no dsu mode
Syntax Description
Defaults
0
Command Modes
Interface configuration
Command History
Usage Guidelines
The local interface configuration must match the remote interface configuration. For example, if you define the data service unit (DSU) interoperability mode as 1 on the local port, you must also do the same on the remote port.
You must know what type of DSU is connected to the remote port to determine if it interoperates with a PA-E3 port adapter or a PA-T3 port adapter. Use mode 0 to connect a PA-E3 port adapter to another PA-E3 port adapter or to a Digital Link DSU (DL3100). Use mode 0 to connect a PA-T3 port adapter to another PA-T3 port adapter or to a Digital Link DSU (DL3100). Use mode 1 to connect a PA-E3 port adapter or a PA-T3 port adapter to a Kentrox DSU. Use mode 2 to connect a PA-T3 port adapter to a Larscom DSU. The dsu mode command enables and improves interoperability with other DSUs.
The dsu mode command enables and improves interoperability with other DSUs.
To verify the DSU mode configured on the interface, use the show controller serial EXEC command.
Examples
The following example sets the DSU mode to 1 on interface 1/0/0:
Router(config)# interface serial 1/0/0Router(config-if)# dsu mode 1Related Commands
dte-invert-txc
On the Cisco 4000 series, you can specify the serial Network Processor Module timing signal configuration. When the board is operating as a DTE, use the dte-invert-txc interface configuration command to invert the TXC clock signal received from the DCE. If the DCE accepts SCTE from the DTE, use the no form of this command.
dte-invert-txc
no dte-invert-txc
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command if the DCE cannot receive SCTE from the DTE, the data is running at high speeds, and the transmission line is long. This prevents phase shifting of the data with respect to the clock.
On the Cisco 4000 series, you can specify the serial Network Processor Module timing signal configuration. When the board is operating as a DTE, the dte-invert-txc command inverts the TXC clock signal it gets from the DCE that the DTE uses to transmit data.
If the DCE accepts SCTE from the DTE, use no dte-invert-txc.
Examples
The following example inverts the TXC on serial interface 0:
Router(config)# interface serial 0Router(config-if)# dte-invert-txcduplex
To configure duplex operation on an interface, use the duplex interface configuration command. To return the system to half-duplex mode, the system default, use the no form of this command.
duplex {full | half | auto}
no duplex
Syntax Description
Defaults
Half-duplex mode
Command Modes
Interface configuration
Command History
Usage Guidelines
To use the auto-negotiation capability (that is, detect speed and duplex modes automatically), you must set both speed and duplex to auto. Setting speed to autonegotiates speed only, and setting duplex to autonegotiates duplex only.
Table 9 describes the access server's performance for different combinations of the duplex and speed modes. The specified duplex command configured with the specified speed command produces the resulting system action.
For the Cisco AS5300, the duplex {full | half | auto} command syntax replaces the following two earlier duplex commands:
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•
You will get the following error messages if you try to use these commands on a Cisco AS5300:
Router(config)# interface fastethernet 0Router(config-if)# full-duplexPlease use duplex command to configure duplex modeRouter(config-if)#Router(config-if)# half-duplexPlease use duplex command to configure duplex modeExamples
The following example shows the different duplex configuration options you can configure on a Cisco AS5300:
Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# interface fastethernet 0Router(config-if)# duplex ?auto Enable AUTO duplex configurationfull Force full duplex operationhalf Force half-duplex operationRelated Commands
e2-clockrate
To configure the serial0 interface for E2 (8 Mhz full duplex) and to shut down the other three serial interfaces (1 to 3), use the e2-clockrate privileged EXEC command. To disable the full duplex E2, use the no form of this command.
e2-clockrate
no e2-clockrate
Syntax Description
There are no arguments or keywords used with this command.
Defaults
No default behavior or values.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
The e2-clockrate privileged EXEC command is an interface configuration command and is seen only with interface serial0. When this command is used, serial interface 0 supports speeds up to E2 (8 MHz full duplex) and the other three serial interfaces (1 to 3) are put in "shutdown" state. Also, running this command displays the warning message, "Serial interface 0 is configured to support E2 rates and serial ports "1-3" are moved to shutdown state."
Examples
The following example shows sample display output for the e2-clockrate EXEC command.
Router(config-if)# e2-clockrateInterface Serial 0 is configured to support clockrates up to E2 (8Mbps)Interfaces serial 1-3 will not be operationalRelated Commands
Configures the clock rate for the hardware connections on serial interfaces such as NIMs and interface processors to an acceptable bit rate.
early-token-release
To enable early token release on Token Ring interfaces, use the early-token-release interface configuration command. To disable this feature, use the no form of the command.
early-token-release
no early-token-release
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Early token release is a method whereby the Token Ring interfaces can release the token back onto the ring immediately after transmitting, rather than waiting for the frame to return. This feature helps increase the total bandwidth of the Token Ring.
The Token Ring Interface Processor (TRIP) on the Cisco 7500 series routers and the Token Ring adapters on the Cisco 7200 series routers all support early token release.
Examples
The following example enables the use of early token release on Token Ring interface 1:
Router(config)# interface tokenring 1Router(config-if)# early-token-releaseOn the Cisco 7500 series, to enable the use of early token release on your Token Ring interface processor in slot 4 on port 1, issue the following configuration commands:
Router(config)# interface tokenring 4/1Router(config-if)# early-token-releaseencapsulation
To set the encapsulation method used by the interface, use the encapsulation interface configuration command.
encapsulation encapsulation-type
Syntax Description
Defaults
The default depends on the type of interface. For example, synchronous serial interfaces default to HDLC and asynchronous interfaces default to SLIP.
Command Modes
Interface configuration
Command History
Usage Guidelines
To use SLIP or PPP, the router or access server 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.
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, "PPP Internet Protocol Control Protocol (IPCP)," 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 Services Commands" in the Networking Protocols Command Reference, Part 1 and the chapter "Configuring IP Services" 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
There is not a no form of this command.
Examples
The following example resets HDLC serial encapsulation on serial interface 1:
Router(config)# interface serial 1Router(config-if)# encapsulation hdlcThe following example enables PPP encapsulation on serial interface 0:
Router(config)# interface serial 0Router(config-if)# encapsulation pppIn the following example, async interface 1 is configured for PPP encapsulation.
Router# configConfiguring from terminal, memory, or network [terminal]?Enter configuration commands, one per line. End with CNTL/Z.Router(config)# interface async 1Router(config-if)# encapsulation pppRelated Commands
fddi burst-count
To allow the FCI card to preallocate buffers to handle bursty FDDI traffic (for example, NFS bursty traffic), use the fddi burst-count interface configuration command. To revert to the default value, use the no form of this command.
fddi burst-count number
no fddi burst-count
Syntax Description
Defaults
3 buffers
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies to the FCI card only.
Note
Examples
The following example sets the number of buffers to 5:
Router(config)# interface fddi 0Router(config-if)# fddi burst-count 5fddi c-min
To set the C-Min timer on the PCM, use the fddi c-min interface configuration command. To revert to the default value, use the no form of this command.
fddi c-min microseconds
no fddi c-min
Syntax Description
Defaults
1600 microseconds
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies to the processor CMT only. You need extensive knowledge of the PCM state machine to tune this timer. Use this command when you run into PCM interoperability problems.
Examples
The following example sets the C-Min timer to 2000 microseconds:
Router(config)# interface fddi 0Router(config-if)# fddi c-min 2000Related Commands
fddi cmt-signal-bits
To control the information transmitted during the connection management (CMT) signaling phase, use the fddi cmt-signal-bits interface configuration command.
fddi cmt-signal-bits signal-bits [phy-a | phy-b]
Syntax Description
signal-bits
A hexadecimal number preceded by 0x; for example, 0x208. The FDDI standard defines 10 bits of signaling information that must be transmitted, as follows:
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•
•
•
•
•
•
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phy-a
(Optional) Selects Physical Sublayer A. The default is 0x008 (hexadecimal) or 00 0000 1000 (binary). Bits 1 and 2 are set to 00 to select Physical A. Bit 3 is set to 1 to indicate "accept any connection."
phy-b
(Optional) Selects Physical Sublayer B. The default is 0x20c (hexadecimal) or 10 0000 1100 (binary). Bits 1 and 2 are set to 10 to select Physical B. Bit 3 is set to 1 to indicate "accept any connection." Bit 9 is set to 1 to select MAC on output. The normal data flow on FDDI is input on Physical A and output on Physical B.
Defaults
The default signal bits for the phy-a and phy-b keywords are as follows:
•
•
Command Modes
Interface configuration
Command History
Usage Guidelines
If neither the phy-a nor phy-b keyword is specified, the signal bits apply to both physical connections.
Caution
Table 10 lists the physical types.
Table 10 FDDI Physical Type Bit Specifications
0
0
Physical A
1
0
Physical B
0
1
Physical S
1
1
Physical M
Table 11 lists the duration bits.
There is not a no form of this command.
Examples
The following example sets the CMT signaling phase to signal bits 0x208 on both physical connections:
Router(config)# interface fddi 0Router(config-if)# fddi cmt-signal-bits 208fddi duplicate-address-check
To turn on the duplicate address detection capability on the FDDI, use the fddi duplicate-address-check interface configuration command. To disable this feature, use the no form of this command.
fddi duplicate-address-check
no fddi duplicate-address-check
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
If you use this command, the Cisco IOS software will detect a duplicate address if multiple stations are sharing the same MAC address. If the software finds a duplicate address, it will shut down the interface.
Examples
The following example enables duplicate address checking on the FDDI:
Router(config)# interface fddi 0Router(config-if)# fddi duplicate-address-checkfddi encapsulate
To specify encapsulating bridge mode on the CSC-C2/FCIT interface card, use the fddi encapsulate interface configuration command. To turn off encapsulation bridging and return the FCIT interface to its translational, nonencapsulating mode, use the no form of this command.
fddi encapsulate
no fddi encapsulate
Syntax Description
This command has no arguments or keywords.
Defaults
The FDDI interface by default uses the SNAP encapsulation format defined in RFC 1042, "Standard for the Transmission of IP Datagrams Over IEEE 802 Networks." It is not necessary to define an encapsulation method for this interface when using the CSC-FCI interface card.
Command Modes
Interface configuration
Command History
Usage Guidelines
The no fddi encapsulate command applies only to CSC-C2/FCIT interfaces, because the CSC-FCI interfaces are always in encapsulating bridge mode. The CSC-C2/FCIT interface card fully supports transparent and translational bridging for the following configurations:
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•
•
The command fddi encapsulate puts the CSC-C2/FCIT interface into encapsulation mode when doing bridging. In transparent mode, the FCIT interface interoperates with earlier versions of the CSC-FCI encapsulating interfaces when performing bridging functions on the same ring.
Caution
The following protocols have problems when bridged between Token Ring and other media: Novell IPX, DECnet Phase IV, AppleTalk, VINES, XNS, and IP. Further, the following protocols may have problems when bridged between FDDI and other media: Novell IPX and XNS. We recommend that these protocols be routed whenever possible.
Examples
The following example sets FDDI interface 1 on the CSC-C2/FCIT interface card to encapsulating bridge mode:
Router(config)# interface fddi 1Router(config-if)# fddi encapsulatefddi frames-per-token
To specify the maximum number of frames that the FDDI interface will transmit per token capture, use the fddi frames-per-token interface configuration command. To revert to the default values, use the no form of this command.
fddi frames-per-token number
no fddi frames-per-token
Syntax Description
number
Maximum number of frames to transmit per token capture. Valid values are from 1 to 10. The default is 3.
Defaults
3 frames
Command Modes
Interface configuration
Command History
Usage Guidelines
Changing the value will increase or decrease the maximum number of frames that the FDDI interface can transmit when it receives a token. Increasing the value does not necessarily mean more frames will be transmitted on each token capture. This is heavily dependent on the traffic load of the specific interface.
When the interface captures a token, it transmits all of the frames that are queued in the interface's transmit ring, up to a maximum value specified by the fddi frames-per-token command.
If there are no frames ready for transmission, the token is passed on, and no frames are transmitted. If there are less than the fddi frames-per-token value in the transmit ring, all frames in the transmit ring are transmitted before the token is passed on. If there are more than the fddi frames-per-token value in the transmit ring, the specified value is transmitted before the token is passed on. The remaining frames in the transmit ring remain queued until the token is captured again.
Examples
The following example shows how to configure the FDDI interface to transmit four frames per token capture:
! Show fddi frames-per-token command options4700(config-if)#fddi frames-per-token ?<1-10> Number of frames per token, default = 3! Specify 4 as the maximum number of frames to be transmitted per token4700(config-if)#fddi frames-per-token 4fddi smt-frames
To enable the SMT frame processing capability on the FDDI, use the fddi smt-frames interface configuration command. To disable this function and prevent the Cisco IOS software from generating or responding to SMT frames, use the no form of this command.
fddi smt-frames
no fddi smt-frames
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use the no form of this command to turn off SMT frame processing for diagnosing purposes. Use the fddi smt-frames command to reenable the feature.
Examples
The following example disables SMT frame processing:
Router(config)# interface fddi 0Router(config-if)# no fddi smt-framesfddi tb-min
To set the TB-Min timer in the physical connection management (PCM), use the fddi tb-min interface configuration command. To revert to the default value, use the no form of this command.
fddi tb-min milliseconds
no fddi tb-min
Syntax Description
milliseconds
Number that sets the TB-Min timer value. The range is 0 to 65,535 ms. The default is 100 ms.
Defaults
100 ms
Command Modes
Interface configuration
Command History
Usage Guidelines
This command applies to the processor CMT only. Use this command when you run into PCM interoperability problems.
Note
Examples
The following example sets the TB-Min timer to 200 ms:
Router(config)# interface fddi 0Router(config-if)# fddi tb-min 200Related Commands
fddi tl-min-time
To control the TL-Min time (the minimum time to transmit a Physical Sublayer, or PHY line state, before advancing to the next physical connection management [PCM] state, as defined by the X3T9.5 specification), use the fddi tl-min-time interface configuration command.
fddi tl-min-time microseconds
Syntax Description
Defaults
30 microseconds
Command Modes
Interface configuration
Command History
Usage Guidelines
Interoperability tests have shown that some implementations of the FDDI standard need more than 30 microseconds to sense a signal.
There is not a no form of this command.
Examples
The following example changes the TL-Min time from 30 microseconds to 100 microseconds:
Router(config)# interface fddi 0Router(config-if)# fddi tl-min-time 100The following example changes the TL-Min time from 30 microseconds to 100 microseconds on a Cisco 7500 series router:
Router(config)# interface fddi 3/0Router(config-if)# fddi tl-min-time 100Related Commands
fddi t-out
To set the t-out timer in the physical connection management (PCM), use the fddi t-out interface configuration command. To revert to the default value, use the no form o
