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Cisco IOS Wide-Area Networking Command Reference, Release 12.3 T
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Introduction
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Wide-Area Networking Commands: A through B
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Wide-Area Networking Commands: C
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Wide-Area Networking Commands: D through E
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Wide-Area Networking Commands: frame-relay adaptive-shaping through frame-relay lmi-type
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Wide-Area Networking Commands: frame-relay local-dlci through fr-atm connect dlci
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Wide-Area Networking Commands: H through L
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Wide-Area Networking Commands: M through R \r\n
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Wide-Area Networking Commands: scrambling cell-payload through show dxi pvc
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Wide-Area Networking Commands: show frame-relay through show vc-group
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Wide-Area Networking Commands: show x25 through svc
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Wide-Area Networking Commands: T through x25 nvc
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Wide-Area Networking Commands: x25 ops through xot access-group
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Table Of Contents
ima differential-delay-maximum
inarp (Frame Relay VC-bundle-member)
hello
To configure the interval used to exchange hello keepalive packets in a Layer 2 control channel, use the hello command in L2TP class configuration mode. To disable the sending of hello keepalive packets, use the no form of this command.
hello seconds
no hello seconds
Syntax Description
Defaults
60 seconds
Command Modes
L2TP class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
You can configure different values with the hello command on the router at each end of a Layer 2 control channel.
Examples
The following example sets an interval of 120 seconds between sendings of hello keepalive messages in pseudowires that have been configured using the L2TP class configuration named "l2tp class1":
Router(config)# l2tp-class l2tp-class1Router(config-l2tp-class)# hello 120Related Commands
l2tp-class
Creates a template of L2TP control plane configuration settings that can be inherited by different pseudowire classes and enters L2TP class configuration mode.
hidden
To hide the attribute-value pair (AVP) values in Layer 2 Tunneling Protocol (L2TP) control messages, use the hidden command in L2TP class configuration mode. To unhide AVPs, use the no form of this command.
hidden
no hidden
Syntax Description
This command has no arguments or keywords.
Defaults
L2TP AVP hiding is disabled.
Command Modes
L2TP class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Use the hidden command to provide additional security for the exchange of control messages between provider edge routers in a Layer 2 Tunnel Protocol Version 3 (L2TPv3) control channel. Because username and password information is exchanged between devices in clear text, it is useful to encrypt L2TP AVP values with the hidden command.
Examples
The following example enables AVP hiding and encrypts AVPs in control messages in L2TPv3 pseudowires that have been configured using the L2TP class configuration named "l2tp class1":
Router(config)# l2tp-class l2tp-class1Router(config-l2tp-class)# hiddenRelated Commands
l2tp-class
Creates a template of L2TP control plane configuration settings that can be inherited by different pseudowire classes and enters L2TP class configuration mode.
hostname (L2TP)
To configure the host name that the router will use to identify itself during Layer 2 Tunnel Protocol Version 3 (L2TPv3) authentication, use the hostname command in L2TP class configuration mode. To remove the host name, use the no form of this command.
hostname name
no hostname name
Syntax Description
Defaults
No host name is specified for L2TPv3 authentication.
Command Modes
L2TP class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
If you do not use the hostname command, the host name of the router is used for L2TPv3 authentication.
Examples
The following example configures the host name "yb2" for a provider edge router used at one end of an L2TPv3 control channel in an L2TPv3 pseudowire that has been configured using the L2TP class configuration named "l2tp class1":
Router(config)# l2tp-class l2tp-class1Router(config-l2tp-class)# hostname yb2Related Commands
idle-timeout
To configure the idle timeout parameter for tearing down an ATM switched virtual circuit (SVC) connection, use the idle-timeout command in the appropriate command mode. To disable the timeout parameter, use the no form of this command.
idle-timeout seconds [minimum-rate]
no idle-timeout seconds [minimum-rate]
Syntax Description
Defaults
The default idle timeout is 300 seconds.
The default minimum rate is 0 kbps.Command Modes
Interface-ATM-VC configuration (for ATM permanent virtual circuits [PVCs] or SVCs)
VC-class configuration (for virtual circuit [VC] classes)Command History
Usage Guidelines
If within the idle timeout period, both the input and output traffic rates are below the minimum-rate, the SVC connection is torn down. The input and output traffic rates are set using the ubr, ubr+, or vbr-nrt command.
If the idle-timeout command is not explicitly configured on an ATM SVC, the SVC inherits the following default configuration (listed in order of next highest precedence):
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Configuration of the idle-timeout command in a VC class assigned to the SVC itself.
•
•
•
Examples
The following example configures an ATM SVC connection inactive after an idle period of 300 seconds. The SVC connection is also configured so that it is considered inactive if the traffic rate is less than 5 kbps.
idle-timeout 300 5Related Commands
ilmi manage
To enable Integrated Local Management Interface (ILMI) management on an ATM permanent virtual circuit (PVC), use the ilmi manage command in the appropriate command mode. To disable ILMI management, use the no form of this command.
ilmi manage
no ilmi manage
Syntax Description
This command has no arguments or keywords.
Defaults
ILMI management is disabled.
Command Modes
Interface-ATM-VC configuration (for an ATM PVC)
VC-class configuration (for a virtual circuit [VC] class)
PVC range configuration (for an ATM PVC range)
PVC-in-range configuration (for an individual PVC within a PVC range)Command History
11.3 T
This command was introduced.
12.1(5)T
This command was made available in PVC range and PVC-in-range configuration modes.
Usage Guidelines
If the ilmi manage command is not explicitly configured on an ATM PVC, the PVC inherits the following default configuration (listed in order of precedence):
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•
•
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Examples
The following example enables ILMI management on the ATM PVC with VPI 0 and VCI 60. The ILMI PVC is assigned the name routerA and the VPI and VCI are 0 and 16, respectively.
interface atm 0/0pvc routerA 0/16 ilmiexitinterface atm 0/0.1 multipointpvc 0/60ilmi manageima active-links-minimum
To set the minimum number of links that must be operating in order for an ATM inverse multiplexing over ATM (IMA) group to remain in service, use the ima active-links-minimum interface configuration command. To remove the current configuration and set the value to the default, use the no form of this command.
ima active-links-minimum number
no ima active-links-minimum number
Syntax Description
Defaults
Links: 1
Command Modes
Interface configuration
Command History
Usage Guidelines
The minimum number of links that should be active for continued group operation depends upon the applications you are using and the speeds they require. ATM frame size and the number of links in a group affect the overhead required by ATM.
Examples
The following example specifies that two links in IMA group 2 must be operational in order for the group to remain in service:
interface atm 0/ima2ima active-links-minimum 2Related Commands
ima clock-mode
To set the transmit clock mode for an ATM inverse multiplexing over ATM (IMA) group, use the ima clock-mode command in interface configuration mode. To remove the current configuration, use the no form of this command.
ima clock-mode {common port | independent}
no ima clock-mode
Syntax Description
Defaults
The default value is common. If no port is specified, the system automatically chooses an active link to provide clocking.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command controls the clock for the IMA group as a whole. If all the links in the group share a clock source, use the common keyword. If all the links use different clock sources, use the independent clock source keyword.
When the common keyword is set, the clock source ATM interface configuration command for the common link determines clocking for all the links in the group.When the independent keyword is set, the clock source ATM interface configuration command is used under each interface to determine clocking individually.
Because the system automatically chooses a replacement for the common link when it fails, any link in an IMA group potentially can provide the recovered transmit clock. For this reason, even when the common keyword is set with a specific link stipulated by the port value, you should use the ATM interface configuration clock source command to make sure that the clock source is configured correctly on each interface in the IMA group.
Examples
The following example specifies that the links in IMA group 2 use a common clock source on link 0:
interface atm0/ima2ima clock-mode common 0Related Commands
ima differential-delay-maximum
To specify the maximum differential delay among the active links in an inverse multiplexing over ATM (IMA) group, use the ima differential-delay-maximum command in interface configuration mode. To restore the default setting, use the no form of this command.
ima differential-delay-maximum milliseconds
no ima differential-delay-maximum milliseconds
Syntax Description
Defaults
25 milliseconds
Command Modes
Interface configuration
Command History
Usage Guidelines
This command helps control latency in ATM-layer traffic by setting a limit on how much latency the slowest link in the group is allowed to introduce (a slower link has a longer propagation delay—for example, due to a longer path through the network or less accurate physical layer clocking—than other links). Setting a high value allows a slow link to continue operating as part of the group, although such a setting means there is added delay to links across the group. A low setting may result in less latency for traffic across the group than a high setting, but it can mean that the system takes a slow link out of operation, reducing total bandwidth.
When a link has been removed from service, it is automatically placed back in service when it meets the delay differential standard. If a link delay exceeds the specified maximum, the link is dropped; otherwise, the IMA feature adjusts for differences in delays so that all links in a group are aligned and carry ATM-layer traffic.
Examples
The following example specifies that the links in IMA group 2 have a maximum differential delay of 50 ms:
interface atm0/ima2ima differential-delay-maximum 50Related Commands
show ima interface atm
Provides information about all configured IMA groups or a specific IMA group.
ima frame-length
To specify the number of cells in inverse multiplexing over ATM (IMA) frames, use the ima frame-length interface configuration command. To remove the current setting and restore the default value, use the no form of this command.
ima frame-length {32 | 64 | 128 | 256}
no ima frame-length {32 | 64 | 128 | 256}
Syntax Description
32
Specifies a value of 32 cells.
64
Specifies a value of 64 cells.
128
Specifies a value of 128 cells.
256
Specifies a value of 256 cells.
Defaults
The default value is 128 cells in a frame.
Command Modes
Interface configuration
Command History
12.0(5)XE
This command was introduced.
12.0(7)XE1
Support for Cisco 7100 series routers added.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
IMA frames are numbered sequentially, and each contains an IMA Control Protocol (ICP) cell at a specific position.
Frame length can affect performance because the greater the total number of frames required to communicate a given number of cells, the greater the overhead for header and other control cells. In addition, shorter frame lengths might diminish performance when translated ATM-Frame Relay interworking occurs.
Examples
On Cisco 7100 and 7200 series routers, the following example specifies that the links in IMA group 2 have a frame length of 64 cells:
interface atm 1/ima2ima frame-length 64ima test
To specify an interface and test pattern for verifying connectivity of all links in an inverse multiplexing over ATM (IMA) group, use the ima test command in interface configuration mode. To stop the test, use the no form of this .
ima test [link port] [pattern pattern-id]
no ima test [link port] [pattern pattern-id]
Syntax Description
Defaults
There is no default for the port value. The default value for pattern-id is 106 (0x6A).
Command Modes
Interface configuration
Command History
Usage Guidelines
To verify link and group connectivity, the pattern is sent from the specified link and looped back from the receiving end across all links belonging to the group as defined at the remote end. Verifying link and group connectivity can help troubleshoot physical link connectivity or configuration problems at the remote end. The local end verifies that the pattern is returned on all links belonging to the group at the local end, and testing is continuous. An IMA control protocol (ICP) cell in each frame identifies the pattern.
When a link is not transmitting or receiving a pattern correctly, the command reports the link number where the problem exists.
Examples
The following example configures link 4 to send test pattern 56:
interface atm 0/ima 2ima test link 2 pattern 56Related Commands
show ima interface atm
Provides information about all configured IMA groups or a specific IMA group.
ima-group
To define physical links as inverse multiplexing over ATM (IMA) group members, use the ima-group command in interface configuration mode for each group member. To remove the port from the group, use the no form of this command.
ima-group group-number
no ima-group group-number
Syntax Description
group-number
Specifies an IMA group number from 0 to 3. IMA groups can span multiple ports on a port adapter but cannot span port adapters.
Defaults
Physical links are not included in IMA groups.
Command Modes
Interface configuration
Command History
Usage Guidelines
When the configuration is first performed or when the group number is changed, the interface is automatically disabled, moved to the new group, and then enabled.
Examples
The following example makes interface 1 on the ATM module in slot 0 a member of IMA group 2:
interface atm0/1ima-group 2Related Commands
inarp
To configure the Inverse Address Resolution Protocol (ARP) time period for an ATM permanent virtual circuit (PVC), virtual circuit (VC) class, or VC bundle, use the inarp command in the appropriate command mode. To restore the default Inverse ARP time period behavior, use the no form of this command.
inarp minutes
no inarp minutes
Syntax Description
Defaults
minutes: 15 minutes.
Command Modes
Interface-ATM-VC configuration (for an ATM PVC)
VC-class configuration (for a VC class)
Bundle configuration (for a VC bundle)
PVC range configuration (for an ATM PVC range)
PVC-in-range configuration (for an individual PVC within a PVC range)Command History
Usage Guidelines
This command is supported for aal5snap encapsulation only when Inverse ARP is enabled. Refer to the encapsulation command for configuring aal5snap encapsulation and the protocol command for enabling Inverse ARP.
If the inarp command is not explicitly configured on an ATM PVC, the PVC inherits the following default configuration (listed in order of precedence):
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•
•
•
Note
For ATM VC bundle management, the Inverse ARP parameter can only be enabled at the bundle level and applied to all VC members of the bundle—that is, it cannot be enabled in bundle-vc configuration mode for individual VC bundle members. To use this command in bundle configuration mode, first enter the bundle command to create the bundle and enter bundle configuration mode.
Examples
The following example sets the Inverse ARP time period to 10 minutes:
inarp 10Related Commands
inarp (Frame Relay VC-bundle-member)
To override the default permanent virtual circuit (PVC) bundle member used for Inverse Address Resolution Protocol (ARP) and specify a different PVC bundle member to handle the Inverse ARP packets, use the inarp command in Frame Relay VC-bundle-member configuration mode. To disable Inverse ARP on the PVC bundle member, use the no form of this command.
inarp
no inarp
Syntax Description
This command has no arguments or keywords.
Defaults
Inverse ARP is handled by the PVC that handles precedence or EXP level 6 or DSCP level 63.
Command Modes
Frame Relay VC-bundle-member configuration
Command History
Usage Guidelines
In each Frame Relay PVC bundle, Inverse ARP by default is handled by the PVC that handles precedence or EXP level 6 or DSCP level 63. In the default case, if the PVC handling Inverse ARP traffic goes down, the Inverse ARP packets are diverted to the PVC that has been configured to handle the bumped traffic for precedence level 6 or DSCP level 63.
Inverse ARP packets arriving on PVCs that are not configured to handle Inverse ARP will be dropped.
If you override the default packet service levels and enable Inverse ARP on a PVC that handles a different precedence or DSCP level, and that PVC goes down, the Inverse ARP packets will be dropped even if another PVC accepts the bumped traffic from the failed PVC.
If the inarp command is entered on two different PVC bundle members, Inverse ARP traffic will be handled by the second entry.
Examples
The following example shows Inverse ARP enabled on PVC 250, which handles DSCP level 60:
interface serial 1/4.1 multipointframe-relay vc-bundle MP-4-dynamicmatch dscppvc 100dscp otherpvc 250dscp 60inarpRelated Commands
interface atm
To configure an ATM interface and enter interface configuration mode, use the interface atm command in global configuration mode.
interface atm interface-number[.subinterface-number {mpls | multipoint | point-to-point}]
Syntax Description
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
10.0
This command was introduced.
12.1(3)T
New optional subinterface types were introduced.
Usage Guidelines
The interface atm command enables you to define a subinterface for a specified type of ATM interface. The subinterface for the ATM interface is created the first time this command is issued with a specified subinterface number.
Examples
For physical ATM interface 3/0, the following command creates an ATM MPLS subinterface having subinterface number 1:
Router# interface atm 3/0.1 mplsRelated Commands
interface atm ima
To configure an inverse multiplexing over ATM (IMA) group, use the interface atm ima global configuration command.
interface atm slot/imagroup-number
Syntax Description
Defaults
By default there are no IMA groups, only individual ATM links.
Command Modes
Global configuration
Command History
Usage Guidelines
If the group does not exist when the command is issued, the command automatically creates the group.
When a port is configured for IMA functionality, it no longer operates as an individual ATM link.
Specifying ATM links as members of a group by using the ima group interface command does not enable the group. You must use the interface atm ima command to create the group.
Examples
The following example configures IMA group 0 on the module in slot 1:
interface atm 1/ima0 ip address 10.18.16.121 255.255.255.192Related Commands
interface cbr
To specify the T1 or E1 constant bit rate interface on an ATM-CES port adapter, and to enter interface configuration mode, use the interface cbr command in global configuration mode.
interface cbr slot/port
Syntax Description
Defaults
No default behavior or values
Command Modes
Global configuration
Command History
Usage Guidelines
The ATM-CES port adapter has four T1 (1.544 Mbps) or four E1 (2.048 Mbps) ports (75- or 120-ohm) that can support both structured (N x 64 kbps) and unstructured ATM Forum-compliant circuit emulation services (CES), and one port that supports an OC-3 (155 Mbps) single-mode intermediate reach interface or a T3 (45 Mbps) or E3 (34 Mbps) standards-based ATM interface.
Examples
The following example specifies the first T1 or E1 port on the ATM-CES port adapter in slot 1:
interface cbr 1/0Related Commands
show ces interface cbr
Displays detailed CBR port information.
show interface cbr
Displays the information about the CBR interface on the ATM-CES port adapter.
interface fr-atm
To create a Frame Relay-ATM Interworking interface on the Cisco MC3810 and to enter Frame Relay-ATM Interworking configuration mode, use the interface fr-atm global configuration command. To delete the Frame Relay-ATM Interworking interface, use the no form of this command.
interface fr-atm number
no interface fr-atm number
Syntax Description
Defaults
Frame Relay-ATM Interworking interface 20 is configured by default.
Command Modes
Global configuration
Command History
Usage Guidelines
This command applies to Frame Relay-ATM Interworking on the Cisco MC3810 only.
Use the interface fr-atm command to enter Frame Relay-ATM interworking interface configuration mode. When you issue this command for the first time, an interface number is created dynamically. You can configure up to 21 Frame Relay-ATM interworking interfaces.
Note
Examples
The following example configures Frame Relay-ATM Interworking interface number 20:
interface fr-atm 20Related Commands
fr-atm connect dlci
Maps a Frame Relay DLCI to an ATM virtual circuit descriptor for FRF.5 Frame Relay-ATM internetworking.
interface mfr
To configure a multilink Frame Relay bundle interface, use the interface mfr command in global configuration mode. To remove the bundle interface, use the no form of this command.
interface mfr number
no interface mfr number
Syntax Description
Defaults
A bundle interface is not configured.
Frame Relay encapsulation is the default encapsulation type for multilink Frame Relay bundle interfaces.Command Modes
Global configuration
Command History
Usage Guidelines
A bundle interface is a virtual interface that serves as the Frame Relay data link and performs the same functions as a physical interface. The bundle is made up of physical serial links, called bundle links. The bundle links within a bundle function as one physical link and one pool of bandwidth. Functionality that you want to apply to the bundle links must be configured on the bundle interface.
The no interface mfr command will work only if all bundle links have been removed from the bundle by using the no encapsulation frame-relay mfr command.
Examples
The following example shows the configuration of a bundle interface called "mfr0". The bundle identification (BID) name "BUNDLE-A" is assigned to the bundle. Serial interfaces 0 and 1 are assigned to the bundle as bundle links.
interface mfr0frame-relay multilink bid BUNDLE-A!interface serial0encapsulation frame-relay mfr0!interface serial1encapsulation frame-relay mfr0Related Commands
interface serial multipoint
To define a logical subinterface on a serial interface to support multiple logical IP subnetworks over Switched Multimegabit Data Service (SMDS), use the interface serial multipoint interface configuration command.
interface serial {interface | slot/port}.subinterface multipoint
Syntax Description
Defaults
This command has no default values.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command only for routers that need knowledge of multiple IP networks. Other routers can be configured with information only about their own networks. A period must be used to separate the interface or slot/port from the subinterface.
Examples
The following example configures serial interface 2 with multipoint logical subinterface 1:
interface serial 2.1 multipointThe following example configures slot 2 port 0 with multipoint logical subinterface 1:
interface serial 2/0.1 multipointRelated Commands
ip dfbit set
To enable the Don't Fragment (DF) bit in the outer Layer 2 header, use the ip dfbit set command in pseudowire class configuration mode. To disable the DF bit setting, use the no form of this command.
ip dfbit set
no ip dfbit set
Syntax Description
This command has no arguments or keywords.
Defaults
For Cisco 12000 series Internet routers, the DF bit is on by default.
For other platforms, the DF bit is off by default.
Command Modes
Pseudowire class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Use this command to set the DF bit on if, for performance reasons, you do not want tunneled packet reassembly to be performed on the router.
Note
Examples
The following example shows how to enable the DF bit in the outer Layer 2 header in pseudowires that were created from the pseudowire class named "ether-pw":
Router(config)# pseudowire-class ether-pwRouter(config-pw)# ip dfbit setRelated Commands
ip pmtu (L2TP)
Enables the discovery of a PMTU for Layer 2 traffic.
pseudowire-class
Specifies the name of an L2TP pseudowire class and enters pseudowire class configuration mode.
ip local interface
To configure the IP address of the provider edge (PE) router interface to be used as the source IP address for sending tunneled packets, use the ip local interface command in pseudowire class configuration mode. To remove the IP address, use the no form of this command.
ip local interface interface-name
no ip local interface interface-name
Syntax Description
interface-name
Name of the PE interface whose IP address is used as the source IP address for sending tunneled packets over a Layer 2 pseudowire.
Defaults
No IP address is configured.
Command Modes
Pseudowire class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Use the same local interface name for all pseudowire classes configured between a pair of PE routers. It is highly recommended that you configure a loopback interface with this command. If you do not configure a loopback interface, the router will choose the "best available local address," which could be any IP address configured on a core-facing interface. This configuration could prevent a control channel from being established.
Note
Note
Examples
The following example shows how to configure the IP address of the local Ethernet interface 0/0 as the source IP address for sending Ethernet packets through an L2TPv3 session:
Router(config)# pseudowire-class ether-pwRouter(config-pw)# ip local interface ethernet 0/0Related Commands
pseudowire-class
Specifies the name of an L2TP pseudowire class and enters pseudowire class configuration mode.
ip pmtu
To enable the discovery of a path maximum transmission unit (MTU) for Layer 2 traffic, use the ip pmtu command in VPDN group configuration mode or pseudowire class configuration mode. To disable path MTU discovery, use the no form of this command.
ip pmtu
no ip pmtu
Syntax Description
This command has no arguments or keywords.
Defaults
Path MTU discovery is disabled.
Command Modes
VPDN group configuration
Pseudowire class configurationCommand History
Usage Guidelines
When issued in VPDN group configuration mode, the ip pmtu command enables any Layer 2 Tunnel Protocol (L2TP) tunnel associated with the specified virtual private dial-up network (VPDN) group to participate in path MTU discovery.
When issued in pseudowire class configuration mode, the ip pmtu command enables any Layer 2 session derived from the specified pseudowire class configuration to participate in path MTU discovery.
Path MTU checks decrease switching performance; therefore this option is disabled by default.
The ip pmtu command enables the processing of Internet Control Message Protocol (ICMP) unreachable messages that indicate fragmentation errors in the IP backbone network carrying the tunneled traffic. The MTU of the Layer 2 session is updated according to the MTU information contained in the ICMP unreachable message.
The ip pmtu command also enables MTU checking for IP packets that are sent into a Layer 2 session with the Don't Fragment (DF) bit set. If an IP packet is larger than the MTU of the tunnel, the packet is dropped and an ICMP unreachable message is sent. If an IP packet is smaller than the MTU of the tunnel, the DF bit in the packet header is reflected from the inner IP header to the tunnel header.
Examples
The following example configures a VPDN group named "dial-in" on an L2TP network server and uses the ip pmtu command to specify that L2TP tunnels will participate in path MTU discovery:
vpdn-group dial-inaccept-dialinprotocol l2tpvirtual-template 1l2tp security crypto-profile l2tpno l2tp tunnel authenticationlcp renegotiation on-mismatchip pmtuThe following example shows how to enable the discovery of the path MTU for pseudowires that have been created from the pseudowire class named "ether-pw":
Router(config)# pseudowire-class ether-pwRouter(config-pw)# ip pmtuRelated Commands
ip dfbit set
Enables the DF bit in the outer Layer 2 tunnel header.
pseudowire-class
Specifies the name of an L2TP pseudowire class and enters pseudowire class configuration mode.
ip protocol
To configure the Layer 2 Tunnel Protocol (L2TP) or Universal Tunnel Interface (UTI) as the IP protocol used for tunneling packets in a Layer 2 pseudowire, use the ip protocol command in pseudowire class configuration mode. To remove the IP protocol configuration, use the no form of this command.
ip protocol {l2tp | uti | protocol-number}
no ip protocol {l2tp | uti | protocol-number}
Syntax Description
Defaults
The default IP protocol is L2TP.
Command Modes
Pseudowire class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Use the ip protocol command to ensure backward compatibility with routers running UTI. This command allows you to configure an L2TPv3 pseudowire between a router running L2TPv3 and a peer router running UTI.
Note
To configure L2TP as the IP protocol that is used to tunnel packets in an L2TPv3 pseudowire, you may enter 115, the IP protocol number assigned to L2TPv3, instead of l2tp in the ip protocol command.
To configure UTI as the IP protocol that is used to tunnel packets in an L2TPv3 pseudowire, you may enter 120, the IP protocol number assigned to UTI, instead of uti in the ip protocol command.
Note
Examples
The following example shows how to configure UTI as the IP protocol used to tunnel packets in an L2TPv3 pseudowire created from the pseudowire class named "ether-pw":
Router(config)# pseudowire-class ether-pwRouter(config-pw)# encapsulation l2tpv3Router(config-pw)# ip protocol utiRelated Commands
ip tcp adjust-mss
To adjust the maximum segment size (MSS) value of TCP SYN packets going through a router, use the ip tcp adjust-mss command in interface configuration mode. To return the MSS value to the default setting, use the no form of this command.
ip tcp adjust-mss max-segment-size
no ip tcp adjust-mss max-segment-size
Syntax Description
Defaults
If the ip tcp adjust-mss command is not configured, the MSS is determined by the originating host.
Command Modes
Interface configuration
Command History
12.2(4)T
This command was introduced.
12.2(8)T
This command was changed from ip adjust-mss to ip tcp adjust-mss.
Usage Guidelines
When a host (usually a PC) initiates a TCP session with a server, it negotiates the IP segment size by using the MSS option field in the TCP SYN packet. The value of the MSS field is determined by the maximum transmission unit (MTU) configuration on the host. The default MSS value for a PC is 1500 bytes.The PPP over Ethernet (PPPoE) standard supports a MTU of only 1492 bytes. The disparity between the host and PPPoE MTU size can cause the router in between the host and the server to drop 1500-byte packets and terminate TCP sessions over the PPPoE network. Even if the path MTU (which detects the correct MTU across the path) is enabled on the host, sessions may be dropped because system administrators sometimes disable the ICMP error messages that must be relayed from the host in order for path MTU to work.
The ip tcp adjust-mss command helps prevent TCP sessions from being dropped by adjusting the MSS value of the TCP SYN packets.
The ip tcp adjust-mss command is effective only for TCP connections passing through the router.
In most cases, the optimum value for the max-segment-size argument is 1452 bytes. This value plus the 20-byte IP header, the 20-byte TCP header, and the 8-byte PPPoE header add up to a 1500-byte packet that matches the MTU size for the Ethernet link.
If you are configuring the ip mtu command on the same interface as the ip tcp adjust-mss command, it is recommended that you use the following commands and values:
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Examples
The following example shows the configuration of a PPPoE client with the MSS value set to 1452:
vpdn enableno vpdn logging!vpdn-group 1request-dialinprotocol pppoe!interface Ethernet0ip address 192.168.100.1.255.255.255.0ip tcp adjust-mss 1452ip nat inside!interface ATM0no ip addressno atm ilmi-keepalivepvc 8/35pppoe client dial-pool-number 1!dsl equipment-type CPEdsl operating-mode GSHDSL symmetric annex Bdsl linerate AUTO!interface Dialer1ip address negotiatedip mtu 1492ip nat outsideencapsulation pppdialer pool 1dialer-group 1ppp authentication pap callinppp pap sent-username sohodyn password 7 141B1309000528!ip nat inside source list 101 Dialer1 overloadip route 0.0.0.0.0.0.0.0 Dialer1access-list permit ip 192.168.100.0.0.0.0.255 anyRelated Commands
ip tos (L2TP)
To configure the Type of Service (ToS) byte in the header of Layer 2 tunneled packets, use the ip tos command in pseudowire class configuration mode. To disable a configured ToS value or IP ToS reflection, use the no form of this command.
ip tos {value value | reflect}
no tos {value value | reflect}
Syntax Description
Defaults
The default ToS value is 0.
Command Modes
Pseudowire class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
The ip tos command allows you to manually configure the value of the ToS byte used in the headers of Layer 2 tunneled packets or to have the ToS value reflected from the IP header of the encapsulated packet.
Note
Note
In addition, you can configure both IP ToS reflection and a ToS priority level (from 0 to 255) for a pseudowire class. In this case, the ToS value in the tunnel header defaults to the value you specify with the ip tos value value command. IP packets received on the Layer 2 interface and encapsulated into the L2TPv3 session have their ToS byte reflected into the outer IP session, overriding the default value configured with the ip tos value value command.
Examples
In the following example, the ToS byte in the headers of tunneled packets in Layer 2 tunnels created from the pseudowire class named "ether-pw" will be reflected from the ToS value in the header of each encapsulated IP packet:
Router(config)# pseudowire-class ether-pwRouter(config-pw)# ip tos reflectRelated Commands
pseudowire-class
Specifies the name of an L2TP pseudowire class and enters pseudowire class configuration mode.
ip ttl
To configure the time-to-live (TTL) byte in the IP headers of Layer 2 tunneled packets, use the ip ttl command in pseudowire class configuration mode. To remove the configured TTL value, use the no form of this command.
ip ttl value
no ip ttl value
Syntax Description
value
Value of the TTL byte in the IP headers of L2TPv3 tunneled packets. The valid values range from 1 to 255. The default value is 255.
Defaults
value: 255
Command Modes
Pseudowire class configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Use this command to set the Don't Fragment (DF) bit on if, for performance reasons, you do not want tunneled packet reassembly to be performed on the router.
Examples
The following example shows how to set the TTL byte to 100 in the IP header of Layer 2 tunneled packets in pseudowires that were created from the pseudowire class named "ether-pw":
Router(config)# pseudowire-class ether-pwRouter(config-pw)# ip ttl 100Related Commands
pseudowire-class
Specifies the name of an L2TP pseudowire class and enters pseudowire class configuration mode.
keepalive (LMI)
To enable the Local Management Interface (LMI) mechanism for serial lines using Frame Relay encapsulation, use the keepalive interface configuration command. To disable this capability, use the no form of this command.
keepalive number
no keepalive
Syntax Description
Defaults
10 seconds
Command Modes
Interface configuration
Command History
Usage Guidelines
The keepalive command enables the keepalive sequence, which is part of the LMI protocol.
Note
Examples
The following example sets the keepalive timer on the server for a period that is two or three seconds faster (has a shorter interval) than the interval set on the keepalive timer of the Frame Relay switch. The difference in keepalive intervals ensures proper synchronization between the Cisco server and the Frame Relay switch.
interface serial 3keepalive 8Related Commands
frame-relay lmi-t392dce
Sets the polling verification timer on a DCE or NNI interface.
l2tp cookie local
To configure the size of the cookie field used in the Layer 2 Tunnel Protocol Version 3 (L2TPv3) headers of incoming packets received from the remote provider edge (PE) peer router, use the l2tp cookie local command in xconnect configuration mode. To remove the configured cookie field parameters, use the no form of this command.
l2tp cookie local size low-value [high-value]
no l2tp cookie local size low-value [high-value]
Syntax Description
Defaults
No cookie value is included in the header of L2TP packets.
Command Modes
Xconnect configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
The l2tp cookie local command specifies the values that the peer PE router includes in the cookie field in L2TPv3 headers of the packets it sends to the local PE router through an L2TPv3 session. These values are required in a static L2TPv3 session.
The cookie field is an optional part of an L2TPv3 header with a length of either 4 or 8 bytes. If you specify an 8-byte length, you must also enter a value for the high-value argument.
Note
Examples
The following example shows how to configure the cookie field of 4 bytes starting at 54321 for the L2TPv3 headers in incoming tunneled packets that were sent from the remote PE peer:
Router(config)# interface Ethernet 0/0Router(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pwRouter(config-if-xconn)# l2tp cookie local 4 54321Related Commands
l2tp cookie remote
To configure the size of the cookie field used in the Layer 2 Tunnel Protocol Version 3 (L2TPv3) headers of outgoing packets sent from the local provider edge (PE) peer router, use the l2tp cookie remote command in xconnect configuration mode. To remove the configured cookie field parameters, use the no form of this command.
l2tp cookie remote size low-value [high-value]
no l2tp cookie remote size low-value [high-value]
Syntax Description
Defaults
No cookie value is included in the header of L2TP packets.
Command Modes
Xconnect configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
The l2tp cookie remote command specifies the values that the local PE router includes in the cookie field in L2TPv3 headers of the packets it sends to the remote PE router through an L2TPv3 session. These values are required in a static L2TPv3 session.
The cookie field is an optional part of an L2TPv3 header with a length of either 4 or 8 bytes. If you specify an 8-byte length, you must also enter a value for the high-value argument.
Examples
The following example shows how to configure the cookie field of 4 bytes starting at 12345 for the L2TPv3 headers in outgoing tunneled packets sent to the remote PE peer:
Router(config)# interface Ethernet 0/0Router(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pwRouter(config-if-xconn)# l2tp cookie remote 4 12345Related Commands
l2tp hello
To specify the use of a hello keepalive setting contained in a specified Layer 2 Tunneling Protocol class configuration for a static Layer 2 Tunnel Protocol Version 3 (L2TPv3) session, use the l2tp hello command in xconnect configuration mode. To disable the sending of hello keepalive messages, use the no form of this command.
l2tp hello l2tp-class-name
no l2tp hello l2tp-class-name
Syntax Description
l2tp-class-name
Specifies the L2TP class configuration in which the hello keepalive interval to be used for the L2TPv3 session is stored.
Defaults
No hello keepalive messages are sent.
Command Modes
Xconnect configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
Because a static L2TPv3 session does not use a control plane to dynamically negotiate control channel parameters, you must use the l2tp hello command to specify an L2TP class configuration that contains the interval for sending hello keepalive messages.
Examples
The following example shows how to configure the time interval for hello keepalive messages stored in the L2TP class configuration named "l2tp-default"s for an Ethernet interface using the configuration settings stored in the pseudowire class named "ether-pw":
Router(config)# interface Ethernet 0/0Router(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pwRouter(config-if-xconn)# l2tp hello lt2p-defaultsRelated Commands
l2tp id
To configure the identifiers used by the local and remote provider edge (PE) routers at each end of a Layer 2 Tunnel Protocol Version 3 (L2TPv3) session, use the l2tp id command in xconnect configuration mode. To remove the configured identifiers for local and remote sessions, use the no form of this command.
l2tp id local-session-ID remote-session-ID
no l2tp id local-session-ID remote-session-ID
Syntax Description
local-session-ID
The identifier used by the local PE router as its local session identifier.
remote-session-ID
The identifier used by the remote PE router as its local session identifier.
Defaults
No session identifiers are configured.
Command Modes
Xconnect configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
The xconnect configuration that binds an attachment circuit to an L2TPv3 pseudowire is not complete without configured values for the local-session-ID and remote-session-ID arguments.
Examples
The following example shows how to configure the identifiers named "222" for the local PE router and "111" for the remote peer in an L2TPv3 session bound to an Ethernet circuit using the L2TPv3 configuration settings stored in the pseudowire class named" ether-pw":
Router(config)# interface Ethernet 0/0Router(config-if)# xconnect 10.0.3.201 123 encapsulation l2tpv3 manual pw-class ether-pwRouter(config-if-xconn)# l2tp id 222 111Related Commands
l2tp-class
To create a template of Layer 2 Tunnel Protocol (L2TP) control plane configuration settings that can be inherited by different pseudowire classes and to enter L2TP class configuration mode, use the l2tp-class command in global configuration mode.
l2tp-class [l2tp-class-name]
Syntax Description
l2tp-class-name
(Optional) Name of the L2TP class. The name argument must be specified if you want to configure multiple sets of L2TP control parameters.
Defaults
No L2TP classes are defined.
Command Modes
Global configuration
Command History
12.0(23)S
This command was introduced.
12.3(2)T
This command was integrated into Cisco IOS Release 12.3(2)T.
Usage Guidelines
The l2tp-class l2tp-class-name command allows you to configure an L2TP class template that consists of configuration settings used by different pseudowire classes. An L2TP class includes the following configuration settings:
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The l2tp-class command enters L2TP class configuration mode, where L2TP control plane parameters are configured.
You must use the same L2TP class in the pseudowire configuration at both ends of a Layer 2 control channel.
Examples
The following example shows how to enter L2TP class configuration mode to create an L2TP class configuration template for the class named "ether-pw":
Router(config)# l2tp-class ether-pwRouter(config-l2tp-class)#Related Commands
lapb interface-outage
To specify the period for which a link will remain connected, even if a brief hardware outage occurs (partial Link Access Procedure, Balanced [LAPB] T3 timer functionality), use the lapb interface-outage interface configuration command.
lapb interface-outage milliseconds
Syntax Description
milliseconds
Number of milliseconds (ms) a hardware outage can last without the protocol disconnecting the service.
Defaults
0 ms, which disables this feature.
Command Modes
Interface configuration
Command History
Usage Guidelines
If a hardware outage lasts longer than the LAPB hardware outage period you select, normal protocol operations will occur. The link will be declared down, and when it is restored, a link setup will be initiated.
Examples
The following example sets the interface outage period to 100 ms. The link remains connected for outages equal to or shorter than that period.
encapsulation lapb dte iplapb interface-outage 100Related Commands
lapb k
To specify the maximum permissible number of outstanding frames, called the window size, use the lapb k interface configuration command.
lapb k window-size
Syntax Description
window-size
Frame count. It can be a value from 1 to the modulo size minus 1 (the maximum is 7 if the modulo size is 8; it is 127 if the modulo size is 128).
Defaults
7 frames
Command Modes
Interface configuration
Command History
Usage Guidelines
If the window size is changed while the protocol is up, the new value takes effect only when the protocol is reset. You will be informed that the new value will not take effect immediately.
When using the Link Access Procedure, Balanced (LAPB) modulo 128 mode (extended mode), you must increase the window parameter k to send a larger number of frames before acknowledgment is required. This increase is the basis for the router's ability to achieve greater throughput on high-speed links that have a low error rate.
This configured value must match the value configured in the peer X.25 switch. Nonmatching values will cause repeated LAPB reject (REJ) frames.
Examples
The following example sets the LAPB window size (the k parameter) to 10 frames:
interface serial 0lapb modulolapb k 10Related Commands
lapb modulo
Specifies the LAPB basic (modulo 8) or extended (modulo 128) protocol mode.
lapb modulo
To specify the Link Access Procedure, Balanced (LAPB) basic (modulo 8) or extended (modulo 128) protocol mode, use the lapb modulo interface configuration command.
lapb modulo modulus
Syntax Description
modulus
Either 8 or 128. The value 8 specifies LAPB's basic mode; the value 128 specifies LAPB's extended mode.
Defaults
Modulo 8
Command Modes
Interface configuration
Command History
Usage Guidelines
The modulo parameter determines which of LAPB's two modes is to be used. The modulo values derive from the fact that basic mode numbers information frames between 0 and 7, whereas extended mode numbers them between 0 and 127. Basic mode is widely available and is sufficient for most links. Extended mode is an optional LAPB feature that may achieve greater throughput on high-speed links that have a low error rate.
The LAPB operating mode may be set on X.25 links as well as LAPB links. The X.25 modulo is independent of the LAPB layer modulo. Both ends of a link must use the same LAPB mode.
When using modulo 128 mode, you must increase the window parameter k to send a larger number of frames before acknowledgment is required. This increase is the basis for the router's ability to achieve greater throughput on high-speed links that have a low error rate.
If the modulo value is changed while the protocol is up, the new value takes effect only when the protocol is reset. You will be informed that the new value will not take effect immediately.
Examples
The following example configures a high-speed X.25 link to use LAPB's extended mode:
interface serial 1encapsulation x25lapb modulo 128lapb k 40clock rate 2000000Related Commands
lapb k
Specifies the maximum permissible number of outstanding frames, called the window size.
lapb n1
To specify the maximum number of bits a frame can hold (the Link Access Procedure, Balanced [LAPB] N1 parameter), use the lapb n1 interface configuration command.
lapb n1 bits
Syntax Description
bits
Maximum number of bits in multiples of eight. The minimum and maximum range is dynamically set. Use the question mark (?) to view the range.
Defaults
The largest (maximum) value available for the particular interface is the default. The Cisco IOS software dynamically calculates N1 whenever you change the maximum transmission unit (MTU), the L2/L3 modulo, or compression on a LAPB interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
The Cisco IOS software uses the following formula to determine the minimum N1 value:
(128 (default packet size) + LAPB overhead + X.25 overhead + 2 bytes of CRC) * 8
The Cisco IOS software uses the following formula to determine for the maximum N1 value:
(hardware MTU + LAPB overhead + X.25 overhead + 2 bytes of CRC) * 8
LAPB overhead is 2 bytes for modulo 8 and 3 bytes for modulo 128.
X.25 overhead is 3 bytes for modulo 8 and 4 bytes for modulo 128.
You need not set N1 to an exact value to support a particular X.25 data packet size. The N1 parameter prevents the processing of any huge frames that result from a "jabbering" interface, an unlikely event.
In addition, the various standards bodies specify that N1 be given in bits rather than bytes. While some equipment can be configured in bytes or will automatically adjust for some of the overhead information present, Cisco devices are configured using the true value, in bits, of N1.
You cannot set the N1 parameter to a value less than that required to support an X.25 data packet size of 128 bytes. All X.25 implementations must be able to support 128-byte data packets. Moreover, if you configure N1 to be less than 2104 bits, you receive a warning message that X.25 might have problems because some nondata packets can use up to 259 bytes.
You cannot set the N1 parameter to a value larger than the default unless the hardware MTU size is first increased.
The X.25 software accepts default packet sizes and calls that specify maximum packet sizes greater than those the LAPB layer supports, but negotiates the calls placed on the interface to the largest value that can be supported. For switched calls, the packet size negotiation takes place end-to-end through the router so the call will not have a maximum packet size that exceeds the capability of either of the two interfaces involved.
Caution
Examples
The following example shows how to use the question mark (?) command to display the minimum and maximum N1 value. In this example, X.25 encapsulation has both the LAPB and X.25 modulo set to 8. Any violation of this N1 range results in an "Invalid input" error message.
router(config)# interface serial 1router(config-if)# lapb n1 ?<1080-12056> LAPB N1 parameter (bits; multiple of 8)The following example sets the N1 bits to 16440:
router(config)# interface serial 0router(config-if)# lapb n1 16440router(config-if)# mtu 2048Related Commands
lapb n2
To specify the maximum number of times a data frame can be sent (the Link Access Procedure, Balanced [LAPB] N2 parameter), use the lapb n2 interface configuration command.
lapb n2 tries
Syntax Description
Defaults
20 transmissions
Command Modes
Interface configuration
Command History
Examples
The following example sets the N2 tries to 50:
interface serial 0lapb n2 50Related Commands
lapb protocol
The lapb protocol command has been replaced by the [protocol | multi] option of the encapsulation lapb command. See the description of the [protocol | multi] option of the encapsulation lapb command earlier in this chapter for more information.
lapb t1
To set the retransmission timer period (the Link Access Procedure, Balanced [LAPB] T1 parameter), use the lapb t1 interface configuration command.
lapb t1 milliseconds
Syntax Description
Defaults
3000 ms
Command Modes
Interface configuration
Command History
Usage Guidelines
The retransmission timer determines how long a transmitted frame can remain unacknowledged before the LAPB software polls for an acknowledgment. The design of the LAPB protocol specifies that a frame is presumed to be lost if it is not acknowledged within T1; a T1 value that is too small may result in duplicated control information, which can severely disrupt service.
To determine an optimal value for the retransmission timer, use the ping privileged EXEC command to measure the round-trip time of a maximum-sized frame on the link. Multiply this time by a safety factor that takes into account the speed of the link, the link quality, and the distance. A typical safety factor is 1.5. Choosing a larger safety factor can result in slower data transfer if the line is noisy. However, this disadvantage is minor compared to the excessive retransmissions and effective bandwidth reduction caused by a timer setting that is too small.
Examples
The following example sets the T1 retransmission timer to 2000 ms:
interface serial 0lapb t1 2000Related Commands
lapb t2
To set the explicit acknowledge deferral timer (the Link Access Procedure, Balanced [LAPB] T2 parameter), use the lapb t2 interface configuration command.
lapb t2 milliseconds
Syntax Description
milliseconds
Time in milliseconds. It can be a value from 1 to 32000. Default is 0 ms (disabled) and the recommended setting.
Defaults
0 ms (disabled), which means that the software will send an acknowledgement as quickly as possible.
Command Modes
Interface configuration
Command History
Usage Guidelines
The explicit acknowledge deferral timer determines the time that the software waits before sending an explicit acknowledgement. The acknowledgement is piggybacked with the data, unless there is no data and then an explicit acknowledgement is sent when the timer expires.
Caution
Related Commands
lapb t4
To set the T4 idle timer, after which the Cisco IOS software sends out a Poll packet to determine whether the link has suffered an unsignaled failure, use the lapb t4 interface configuration command.
lapb t4 seconds
Syntax Description
Defaults
0 seconds
Command Modes
Interface configuration
Command History
Usage Guidelines
Any non-zero T4 duration must be greater than T1, the Link Access Procedure, Balanced (LAPB) retransmission timer period.
Examples
The following example will poll the other end of an active link if it has been 10 seconds since the last frame was received. If the far host has failed, the service will be declared down after n2 tries are timed out.
interface serial0encapsulation x25lapb t4 10Related Commands
logging event frame-relay x25
To enable notification of X.25 Annex G session status changes to be displayed on a console or system log, use the logging event frame-relay x25 command in interface configuration mode. To disable notification, use the no form of this command.
logging event frame-relay x25
no logging event frame-relay x25
Syntax Description
This command has no arguments or keywords.
Defaults
X.25 Annex G session status change notifications are not enabled.
Command Modes
Interface configuration
Command History
Examples
The following example shows how to enable notification of X.25 Annex G session status changes to be displayed on a console or system log using the logging event frame-relay x25 interface configuration command:
Router(config-if)# logging event frame-relay x25The following is an example of the Annex G status change notifications:
%X25-5-UPDOWN: Interface <interface> - DLCI <dlci number> X.25 packet layer changed state to DOWN%X25-5-UPDOWN: Interface <interface> - DLCI <dlci number> X25 packet layer changed state to UPloopback
To loop packets back to the interface for testing, use the loopback interface configuration command with or without an optional keyword. To remove the loopback, use the no form of this command.
Cisco 2600 and 3600 Series
loopback [line | local | payload | remote]
no loopback [line | local | payload | remote]
Cisco 7100, 7200, and 7500 Series
For T1 lines:
loopback {diagnostic | local {payload | line} | remote {iboc | esf {payload | line}}}
For E1 lines:
loopback {diagnostic | local {payload | line}}
no loopback
Syntax Description
Defaults
The line keyword is the default.
Loopback is disabled by default.Command Modes
Interface configuration
Command History
Usage Guidelines
You can use a loopback test on lines to detect and distinguish equipment malfunctions caused either by line and channel service unit/digital service unit (CSU/DSU) or by the interface. If correct data transmission is not possible when an interface is in loopback mode, the interface is the source of the problem.
The local loopback does not generate any packets automatically. Instead, the ping command is used.
Examples
The following example sets up local loopback diagnostics:
interface atm 1/0 loopback localloopback (ATM)
To configure the ATM interface into loopback mode, use the loopback interface configuration command. To remove the loopback, use the no form of this command.
loopback [cell | line | payload]
no loopback [cell | line | payload]
Syntax Description
Defaults
line
Command Modes
Interface configuration
Command History
11.0
This command was introduced.
11.1
The following keywords were removed:
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Usage Guidelines
This command is useful for testing because it loops all packets from the ATM interface back to the interface as well as directing the packets to the network.
Use the loopback line command to check that the PA-A3 port adapter is working by looping the receive data back to the transmit data.
Examples
The following example loops all packets back to the ATM interface:
interface atm 4/0loopbackRelated Commands
