Table Of Contents
interface fastethernet
To select a particular Fast Ethernet interface for configuration, use the interface fastethernet global configuration command.
Cisco 4500 and 4700 series
interface fastethernet number
Cisco 7200 series
interface fastethernet slot/port
Cisco 7500 series
interface fastethernet slot/port-adapter/port
Syntax Description
Defaults
Standard Advanced Research Projects Agency (ARPA) encapsulation is configured.
Command Modes
Global configuration
Command History
11.2
This command was introduced.
11.3
Default encapsulation type changed to ARPA.
Examples
The following example configures Fast Ethernet interface 0 for standard ARPA encapsulation (the default setting) on a Cisco 4500 or 4700 series routers:
interface fastethernet 0Related Commands
show interfaces fastethernet
Displays information about the FastEthernet interfaces.
interface group-async
To create a group interface that will serve as master, to which asynchronous interfaces can be associated as members, use the interface group-async global configuration command. Use the no form of the command to restore the default.
interface group-async unit-number
no interface group-async unit-number
Syntax Description
Defaults
No interfaces are designated as group masters.
Command Modes
Global configuration
Usage Guidelines
Using the interface group-async command, you create a single asynchronous interface to which other interfaces are associated as members using the group-range command. This one-to-many configuration allows you to configure all associated member interfaces by entering one command on the group master interface, rather than entering this command on each individual interface. You can create multiple group masters on a device; however, each member interface can only be associated with one group.
Examples
The following example defines asynchronous group master interface 0:
interface group-async 0Related Commands
interface port-channel
To specify a Fast EtherChannel and enter interface configuration mode, use the interface port-channel global configuration command.
interface port-channel channel-number
Syntax Description
Defaults
No Fast EtherChannel is specified.
Command Modes
Global configuration
Command History
Usage Guidelines
The Fast EtherChannel feature allows multiple Fast Ethernet point-to-point links to be bundled into one logical link to provide bidirectional bandwidth of up to 800 Mbps. Fast EthernetChannel can be configured between Cisco 7000 (with RSP7000 and RSP7000CI) and Cisco 7500 series routers or between a Cisco 7000 (with RSP7000 and RSP7000CI) or Cisco 7500 series router and a Catalyst 5000 switch.
You can configure the port-channel interface as you would do to any Fast Ethernet interface.
After you create a port-channel interface, you assign Fast Ethernet interfaces (up to four) to it. For information on how to assign a Fast Ethernet interface to a port-channel interface, refer to the channel-group interface configuration command.
CautionThe port-channel interface is the routed interface. Do not enable Layer 3 addresses on the physical Fast Ethernet interfaces. Do not assign bridge groups on the physical Fast Ethernet interfaces because it creates loops. Also, you must disable spanning tree.
Caution
Note
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Examples
The following example creates a port-channel interface with a channel group number of 1 and adds three Fast Ethernet interfaces to port-channel 1:
Router(config)# interface port-channel 1Router(config-if)# ip address 1.1.1.10 255.255.255.0Router(config)# interface fastethernet 1/0/0Router(config-if)# channel-group 1Router(config)# interface fastethernet 4/0/0Router(config-if)# channel-group 1Router(config)# interface fastethernet 5/0/0Router(config-if)# channel-group 1Related Commands
interface vg-anylan
Use the interface vg-anylan global configuration command to specify the interface on a 100VG-AnyLAN port adapter and enter interface configuration mode on Cisco 7200 series routers and Cisco 7500 series routers.
interface vg-anylan slot/port-adapter/port VIP Cards in Cisco 7500 Series Routers
interface vg-anylan slot/port Cisco 7200 Series Routers
Syntax Description
Defaults
No interfaces are specified.
Command Modes
Global configuration
Command History
Usage Guidelines
The 100VG-AnyLAN port adapter provides a single interface port that is compatible with and specified by IEEE 802.12. The 100VG-AnyLAN port adapter provides 100 Mbps over Category 3 or Category 5 unshielded twisted-pair (UTP) cable with RJ-45 terminators, and supports IEEE 802.3 Ethernet packets.
You configure the 100VG-AnyLAN port adapter as you would any Ethernet or Fast Ethernet interface. The 100VG-AnyLAN port adapter can be monitored with the IEEE 802.12 Interface MIB.
Examples
The following example specifies the 100VG-AnyLAN port adapter in the first port adapter in slot 1:
interface vg-anylan 1/0/0Related Commands
international bit
To set the E3 international bit in the G.751 frame used by the PA-E3 port adapter, use the international bit interface configuration command. To return to the default international bit, use the no form of this command.
international bit {0 | 1} {0 | 1}
no international bit
Syntax Description
0 | 1
Specifies the value of the first international bit in the G.751 frame.
0 | 1
Specifies the value of the second international bit in the G.751 frame.
Defaults
0 0 international bit
Command Modes
Interface configuration
Command History
Usage Guidelines
The international bit command sets bits 6 and 8, respectively, of set II in the E3 frame.
To verify the international bit configured on the interface, use the show controller serial EXEC command.
Examples
The following example sets the international bit to 1 1 on the PA-E3 port adapter in slot 1, port-adapter slot 0, interface 0:
interface serial 1/0/0international bit 1 1Related Commands
national bit
Sets the E3 national bit in the G.751 frame used by the PA-E3 port adapter.
show controllers serial
Displays information that is specific to the interface hardware.
invert data
To invert the data stream, use the invert data interface configuration command. This command applies only to the Cisco 7000 series routers with the RSP7000 and RSP7000CI, Cisco 7200 series routers, and Cisco 7500 series routers. Use the no form of this command to disable inverting the data stream.
invert data
no invert data
Syntax Description
This command has no arguments or keywords.
Defaults
Data is not inverted.
Command Modes
Interface configuration
Command History
Usage Guidelines
T1 Line without B8ZS Encoding
If the interface on the PA-8T and PA-4T+ synchronous serial port adapters and the PA-T3 and PA-2T3 synchronous serial port adapters is used to drive a dedicated T1 line that does not have B8ZS encoding (a method to avoid 15 zeros), the data stream must be inverted (both TXD and RXD) either in the connecting CSU/DSU or the interface.
Inverting is a method of avoiding excessive zeroes that is superseded by the use of B8ZS encryption. This option could be needed for use with legacy equipment that supports this option. By inverting the HDLC data stream, the HDLC zero insertion algorithm becomes a ones insertion algorithm that satisfies the T1 requirements. Be careful not to invert data both on the interface and on the CSU/DSU as two data inversions will cancel each other out.
AMI Line Coding
If the interface on the CT3IP uses AMI line coding, you must also invert the data on the T1 channel. For more information, see the t1 linecode controller configuration command.
Examples
The following example inverts data on serial interface 3/1/0:
interface serial 3/1/0invert dataRelated Commands
t1 linecode
Specifies the type of linecoding used by the T1 channels on the CT3IP in Cisco 7500 series routers.
invert rxclock
To configure UIO serial port 0 or 1 on the Cisco MC3810 when the cable connected is DCE type, use the invert rxclock interface configuration command. The command inverts the phase of the RX clock on the UIO serial interface, which does not use the T1/E1 interface. To disable the phase inversion, use the no form of this command.
invert rxclock
no invert rxclock
Syntax Description
This command has no arguments or keywords.
Defaults
Receive clock signal is not inverted.
Command Modes
Interface configuration
Command History
Examples
The following example inverts the clock signal on serial interface 1:
interface serial 1invert rxclockinvert-transmit-clock
The invert txclock command replaces this command. Refer to the description of invert txclock for information on the transmit clock signal.
invert txclock
To invert the transmit (TX) clock signal, use the invert txclock interface configuration command. To return the TX clock signal to its initial state, use the no form of this command.
invert txclock
no invert txclock
Syntax Description
This command has no arguments or keywords.
Defaults
Transmit clock signal is not inverted.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
11.3
This command was modified to change the command from invert-transmit-clock to invert txclock.
Usage Guidelines
Delays between the SCTE clock and data transmission indicate that the transmit clock signal might not be appropriate for the interface rate and length of cable being used. Different ends of the wire can have variances that differ slightly.The invert txclock command compensates for these variances. This command replaces the invert-transmit-clock command.
Systems that use long cables or cables that are not transmitting the TxC signal (transmit echoed clock line, also known as TXCE or SCTE clock) can experience high error rates when operating at the higher transmission speeds. For example, if a PA-8T synchronous serial port adapter is reporting a high number of error packets, a phase shift might be the problem. Inverting the clock might correct this shift.
When a PA-8T or PA-4T+ port adapter interface is DTE, the invert txclock command inverts the TxC signal it received from the remote DCE. When the PA-8T or PA-4T+ port adapter interface is DCE, this command changes the signal back to its original phase.
Examples
The following example inverts the clock signal on serial interface 3/0:
interface serial 3/0invert txclockkeepalive
To set the keepalive timer for a specific interface, use the keepalive interface configuration command. To turn off keepalives entirely, use the no form of this command.
keepalive [seconds]
no keepalive [seconds]
Syntax Description
Defaults
10 seconds
Command Modes
Interface configuration
Command History
Usage Guidelines
You can configure the keepalive interval, which is the frequency at which the Cisco IOS software sends messages to itself (Ethernet and Token Ring) or to the other end (serial), to ensure a network interface is alive. The interval in previous software versions was 10 seconds; it is now adjustable in 1-second increments down to 1 second. An interface is declared down after three update intervals have passed without receiving a keepalive packet.
Setting the keepalive timer to a low value is very useful for rapidly detecting Ethernet interface failures (transceiver cable disconnecting, cable unterminated, and so on).
A typical serial line failure involves losing Carrier Detect (CD) signal. Because this sort of failure is typically noticed within a few milliseconds, adjusting the keepalive timer for quicker routing recovery is generally not useful.
Note
Examples
The following example sets the keepalive interval to 3 seconds:
interface ethernet 0keepalive 3lex burned-in-address
To set the burned-in MAC address for a LAN Extender interface, use the lex burned-in-address interface configuration command. To clear the burned-in MAC address, use the no form of this command.
lex burned-in-address ieee-address
no lex burned-in-address
Syntax Description
Defaults
No burned-in MAC address is set.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command only on a LAN Extender interface that is not currently active (not bound to a serial interface).
Examples
The following example sets the burned-in MAC address on LAN Extender interface 0:
interface serial 4encapsulation pppinterface lex 0lex burned-in-address 0000.0c00.0001ip address 131.108.172.21 255.255.255.0lex input-address-list
To assign an access list that filters on MAC addresses, use the lex input-address-list interface configuration command. To remove an access list from the interface, use the no form of this command.
lex input-address-list access-list-number
no lex input-address-list
Syntax Description
access-list-number
Number of the access list you assigned with the access-list global configuration command. It can be a number from 700 to 799.
Defaults
No access lists are preassigned to a LAN Extender interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
The no lex input-address-list command first appeared in Cisco IOS Release 10.0.
Use the lex input-address-list command to filter the packets that are allowed to pass from the LAN Extender to the core router. The access list filters packets based on the source MAC address.
The LAN Extender interface does not process MAC-address masks. Therefore, you should omit the mask from the access-list commands.
For LAN Extender interfaces, an implicit permit everything entry is automatically defined at the end of an access list. Note that this default differs from other access lists, which have an implicit deny everything entry at the end of each access list.
Examples
The following example applies access list 710 to LAN Extender interface 0. This access list denies all packets from MAC address 0800.0214.2776 and permits all other packets.
access-list 710 deny 0800.0214.2776interface lex 0lex input-address-list 710Related Commands
access-list
Configures the access list mechanism for filtering frames by protocol type or vendor code.
lex input-type-list
Use the lex input-type-list interface configuration command to assign an access list that filters Ethernet packets by type code. To remove an access list from the interface, use the no form of this command.
lex input-type-list access-list-number
no lex input-type-list
Syntax Description
access-list-number
Number of the access list you assigned with the access-list global configuration command. It can be a number in the range 200 to 299.
Defaults
No access lists are preassigned to a LAN Extender interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
Filtering is done on the LAN Extender chassis.
The LAN Extender interface does not process masks. Therefore, you should omit the mask from the access-list commands.
For LAN Extender interfaces, an implicit permit everything entry is automatically defined at the end of an access list. Note that this default differs from other access lists, which have an implicit deny everything entry at the end of each access list.
Examples
The following example applies access list 220 to LAN Extender interface 0. This access list denies all AppleTalk packets (packets with a type field of 0x809B) and permits all other packets.
access-list 220 deny 0x809B 0x0000interface lex 0lex input-type-list 220Related Commands
access-list
Configures the access list mechanism for filtering frames by protocol type or vendor code.
lex priority-group
Use the lex priority-group interface configuration command to activate priority output queuing on the LAN Extender. To disable priority output queuing, use the no form of this command.
lex priority-group group
no lex priority-group
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
To define queuing priorities, use the priority-list protocol global configuration command. Note that you can use only the following forms of this command:
priority-list list protocol protocol {high | medium | normal | low}
priority-list list protocol bridge {high | medium | normal | low} list list-number
If you specify a protocol that does not have an assigned Ethernet type code, such as x25, stun, or pad, it is ignored and will not participate in priority output queuing.
Examples
The following example activates priority output queuing on LAN Extender interface 0:
priority-list 5 protocol bridge medium list 701lex interface 0lex priority-group 5Related Commands
priority-list protocol
Establishes queueing priorities based on the protocol type.
lex retry-count
Use the lex retry-count interface configuration command to define the number of times to resend commands to the LAN Extender chassis. To return to the default value, use the no form of this command.
lex retry-count number
no lex retry-count [number]
Syntax Description
number
Number of times to retry sending commands to the LAN Extender. It can be a number in the range 0 to 100.
Defaults
10
Command Modes
Interface configuration
Command History
Usage Guidelines
After the router has sent a command the specified number of times without receiving an acknowledgment from the LAN Extender, it stops sending the command altogether.
Examples
The following example resends commands 20 times to the LAN Extender:
lex interface 0lex retry-count 20Related Commands
lex timeout
Defines the amount of time to wait for a response from the LAN Extender.
lex timeout
Use the lex timeout interface configuration command to define the amount of time to wait for a response from the LAN Extender. To return to the default time, use the no form of this command.
lex timeout milliseconds
no lex timeout [milliseconds]
Syntax Description
milliseconds
Time, in milliseconds, to wait for a response from the LAN Extender before resending the command. It can be a number in the range 500 to 60000.
Defaults
2000 milliseconds (2 seconds)
Command Modes
Interface configuration
Command History
Usage Guidelines
The lex timeout command defines the amount of time that the router waits to receive an acknowledgment after having sent a command to the LAN Extender.
Examples
The following example causes unacknowledged packets to be resent at 4-second intervals:
lex interface 0lex timeout 4000Related Commands
lex retry-count
Defines the number of times to resend commands to the LAN Extender chassis.
linecode
Use the linecode controller configuration command to select the line-code type for T1 or E1 line.
linecode {ami | b8zs | hdb3}
Syntax Description
Defaults
AMI is the default for T1 lines.
High-density bipolar 3 is the default for E1 lines.
Command Modes
Controller configuration
Command History
Usage Guidelines
Use this command in configurations where the router or access server must communicate with T1 fractional data lines. The T1 service provider determines which line-code type, either ami or b8zs, is required for your T1 circuit. Likewise, the E1 service provider determines which line-code type, either ami or hdb3, is required for your E1 circuit.
Examples
The following example specifies B8ZS as the line-code type:
linecode b8zslink-test
To reenable the link-test function on a port on an Ethernet hub of a Cisco 2505 or Cisco 2507, use the link-test hub configuration command. Use the no form of this command to disable this feature if a pre-10BaseT twisted-pair device not implementing link test is connected to the hub port.
link-test
no link-test
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Hub configuration
Command History
Usage Guidelines
This command applies to a port on an Ethernet hub only. Disable this feature if a 10BaseT twisted-pair device at the other end of the hub does not implement the link test function.
Examples
The following example disables the link test function on hub 0, ports 1 through 3:
hub ethernet 0 1 3no link-testRelated Commands
hub
Enables and configures a port on an Ethernet hub of a Cisco 2505 or Cisco 2507.
local-lnm
To enable Lanoptics Hub Networking Management of a PCbus Token Ring interface, use the local-lnm interface configuration command. Use the no form of this command to disable Lanoptics Hub Networking Management.
local-lnm
no local-lnm
Syntax Description
This command has no arguments or keywords.
Defaults
Management is not enabled.
Command Modes
Interface configuration
Command History
Usage Guidelines
The Token Ring interface on the AccessPro PC card can be managed by a remote LAN manager over the PCbus interface. At present, the Lanoptics Hub Networking Management software running on an IBM compatible PC is supported.
Examples
The following example enables Lanoptics Hub Networking Management:
local-lnmlogging event
To enable notification of interface, subinterface, and Frame Relay data link connection identifier (DLCI) data link status changes, use the logging event command in interface configuration mode. To disable notification, use the no form of this command.
logging event {dlci-status-change | link-status | subif-link-status}
no logging event {dlci-status-change | link-status | subif-link-status}
Syntax Description
Defaults
For system images, notification of interface, subinterface, and Frame Relay DLCI data link status changes is enabled by default.
For boot images, notification of Frame Relay subinterface and DLCI data link status changes is disabled by default. Notification of interface data link status changes is enabled by default.
Command Modes
Interface configuration
Command History
Examples
The following example shows how to enable notification of subinterface link status changes:
Router(config-if)# logging event subif-link-statusThe following are examples of Frame Relay DLCI and subinterface status change notification messages filtered by the logging event command:
00:16:22: %FR-5-DLCICHANGE: Inteface Serial3/0/0:1 - DLCI 105 state changed to INACTIVE00:16:22: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial3/0/0:1.5, changed state to downloopback (interface)
To diagnose equipment malfunctions between interface and device, use the loopback (interface) configuration command. The no form of this command disables the test.
loopback
no loopback
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
On HSSI serial interface cards, the loopback function configures a two-way internal and external loop on the HSA applique of the specific interface.
On MCI and SCI serial interface cards, the loopback functions when a CSU/DSU or equivalent device is attached to the router or access server. The loopback command loops the packets through the CSU/DSU to configure a CSU loop, when the device supports this feature.
On the MCI and MEC Ethernet cards, the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
On the CSC-FCI FDDI card, the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
On all Token Ring interface cards (except the 4-megabit CSC-R card), the interface receives back every packet it sends when the loopback command is enabled. Loopback operation has the additional effect of disconnecting network server functionality from the network.
Note
To show interfaces currently in loopback operation, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on Ethernet interface 4:
interface ethernet 4 loopbackRelated Commands
down-when-looped
Configures an interface to inform the system it is down when loopback is detected.
show interfaces loopback
Displays information about the loopback interface.
loopback (E3/T3 interface)
To loop the serial interface on a PA-E3 or a PA-T3 port adapter, use the loopback (E3/T3 interface) configuration command. To remove the loopback, use the no form of this command.
PA-E3 port adapter
loopback {dte | local | network {line | payload}}
no loopback
PA-T3 port adapter
loopback {dte | local | network {line | payload} | remote}
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
To verify that a loopback is configured on the interface, use the show interface serial or show interfaces loopback EXEC command.
Examples
The following example configures the serial interface located in slot 3/0/0 for a local loopback:
interface serial 3/0/0loopback localRelated Commands
show controllers serial
Displays information that is specific to the interface hardware.
loopback (T1 interface)
To loop individual T1 channels on the Channelized T3 Interface Processor (CT3IP) in Cisco 7000 series routers with the RSP7000 and RSP7000CI and in Cisco 7500 series routers, use the loopback (T1 interface) configuration command. Use the no form of this command to remove the loopback.
loopback [local | network {line | payload} | remote {line {fdl {ansi | bellcore} | inband} | payload [fdl] [ansi]}]
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
To better diagnose T1 provisioning problems, you can place the remote CSU or remote SmartJack into loopback. The loopback remote line fdl interface configuration command allows you to place either the CSU or the SmartJack into loopback:
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When both are configured, transmission of LOF indication (yellow alarm) takes priority over transmission of some FDL messages.
If the remote loopback appears not to be working, use the show cont t3 command to determine if the given T1 is currently attempting to transmit a LOF indication (yellow alarm):
Router# show controllers t3 0/0/0:2T3 0/0/0 is up.CT3 H/W Version: 5, CT3 ROM Version: 1.2, CT3 F/W Version: 2.5.9Mx H/W version: 2, Mx ucode ver: 1.34T1 2 is down, speed: 1536 kbs, non-inverted datatimeslots: 1-24FDL per AT&T 54016 spec.Transmitter is sending LOF Indication.Receiver is getting AIS.If the transmitter is sending a LOF indication, as in the previous example, stop the transmission of the LOF indication (yellow alarm) with the no t1 yellow generation configuration command as shown in the following example:
Router(config)# controllers t3 0/0/0Router(config-controll)# no t1 2 yellow generationRouter(config-controll)# ^DTo verify that the transmission of the LOF indication (yellow alarm) has stopped, use the show cont t3 command:
Router# show cont t3 0/0/0:2T3 0/0/0 is up.CT3 H/W Version: 5, CT3 ROM Version: 1.2, CT3 F/W Version: 2.5.9Mx H/W version: 2, Mx ucode ver: 1.34T1 2 is down, speed: 1536 kbs, non-inverted datatimeslots: 1-24FDL per AT&T 54016 spec.Receiver is getting AIS.Framing is ESF, Line Code is B8ZS, Clock Source is Internal.Yellow Alarm Generation is disabledThen retry the remote loopback command. When diagnosis is complete, remember to re-enable the LOF indication (yellow alarm).
You can also loopback all the T1 channels by using the loopback (CT3IP) interface configuration command.
Examples
The following example configures T1 channel 5 for a local loopback:
interface serial 3/0/0:5loopback localRelated Commands
loopback (T3 controller)
Loops the entire T3 (all 28 T1 channels) on the CT3IP in Cisco 7500 series routers.
loopback (T3 controller)
To loop the entire T3 (all 28 T1 channels) on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the loopback (T3 controller) configuration command. Use the no form of this command to remove the loopback.
loopback [local | network | remote]
no loopback
Syntax Description
Defaults
Disabled
Command Modes
Controller configuration
Command History
Usage Guidelines
Use this command for troubleshooting purposes.
You can also loopback each T1 channel by using the loopback (T1 interface) configuration command.
For more information, refer to the "Troubleshoot the T3 and T1 Channels" section in the "Configuring Serial Interfaces" chapter of the Cisco IOS Interface Configuration Guide.
Examples
The following example configures the CT3IP for a local loopback:
controller t3 3/0/0loopback localRelated Commands
Loops packets through a CSU/DSU, over a DS3 link or a channelized T1 link, to the remote CSU/DSU and back.
loopback applique
To configure an internal loop on the HSSI applique, use the loopback applique interface configuration command. To remove the loop, use the no form of this command.
loopback applique
no loopback applique
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command loops the packets within the applique, to provide a way to test communication within the router or access server. It is useful for sending pings to yourself to check functionality of the applique.
To show interfaces currently in loopback operation, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the HSSI applique:
interface serial 1 loopback appliqueRelated Commands
loopback dte
To loop packets back to the DTE from the CSU/DSU, when the device supports this feature, use the loopback dte interface configuration command. To remove the loop, use the no form of this command.
loopback dte
no loopback dte
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is useful for testing the DTE-to-DCE cable.
This command is used to test the performance of the integrated CSU/DSU. Packets are looped from within the CSU/DSU back to the serial interface of the router. Send a test ping to see if the packets successfully looped back. To cancel the loopback test, use the no loopback dte command.
When using the 4-wire 56/64-kbps CSU/DSU module, an out-of-service signal is transmitted to the remote CSU/DSU.
To show interfaces currently in loopback operation, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the DTE interface:
router(config)# interface serial 0router(config-if)# loopback dterouter(config-if)#Related Commands
loopback line
Use the loopback line interface configuration command, to loop packets completely through the CSU/DSU to configure the CSU loop. To remove the loop, use the no form of this command.
loopback line [payload]
no loopback line [payload]
Syntax Description
payload
(Optional) Configures a loopback point at the DSU and loops back data to the network on an integrated CSU/DSU.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is useful for testing the DCE device (CSU/DSU) itself. When the loopback line command is configured on the 2-wire 56-kbps CSU/DSU module or the 4-wire 56/64-kbps CSU/DSU modules, the network data loops back at the CSU and the router data loops back at the DSU. If the CSU/DSU is configured for switched mode, you must have an established connection to perform a payload-line loopback. To loop the received data through the minimum amount of CSU/DSU circuitry, issue the loopback line command.
When you issue the loopback line payload command on an integrated CSU/DSU module, the router cannot transmit data through the serial interface for the duration of the loopback. Choosing the DSU as a loopback point loops the received-network data through the maximum amount of CSU/DSU circuitry. Data is not looped back to the serial interface. An active connection is required when operating in switched mode for payload loopbacks.
If you enable the loopback line command on the fractional T1/T1 module, the CSU/DSU performs a full-bandwidth loopback through the CSU portion of the module and data transmission through the serial interface is interrupted for the duration of the loopback. No reframing or corrections of bipolar violation errors or cyclic redundancy check (CRC) errors are performed. When you configure the loopback line payload command on the FT1/T1 module, the CSU/DSU performs a loopback through the DSU portion of the module. The loopback line payload command reframes the data link, regenerates the signal, and corrects bipolar violations and Extended Super Frame CRC errors.
When performing a T1-line loopback with Extended Super Frame, communication over the facilities data link is interrupted, but performance statistics are still updated. To show interfaces currently in loopback operation, use the show service-module EXEC command.
To show interfaces currently in loopback operation on other routers, use the show interfaces loopback EXEC command.
Examples
The following example configures the loopback test on the DCE device:
interface serial 1 loopback lineThe following example shows how to configure a payload loopback on a Cisco 2524 or 2525 router:
Router1(config-if)#loopback line payloadLoopback in progressRouter1(config-if)#no loopback lineThe following example shows the output on a Cisco 2524 or 2525 router when you loop a packet in switched mode without an active connection:
Router1(config-if)#service-module 56k network-type switchedRouter1(config-if)#loopback line payloadNeed active connection for this type of loopback% Service module configuration command failed: WRONG FORMAT.Related Commands
Guest
