-
Cisco IOS Interface and Hardware Component Command Reference, Release 12.3
-
Introduction
-
Interface and Hardware Component Commands: A through C
-
Interface and Hardware Component Commands: D through H
-
Interface and Hardware Component Commands: I through L
-
Interface and Hardware Component Commands: M through R
-
Interface and Hardware Component Commands: scramble through show aps
-
Interface and Hardware Component Commands: show compress through show hub
-
Interface and Hardware Component Commands: show interfaces through syscon source-interface
-
Interface and Hardware Component Commands: T through Z
-
Table Of Contents
transmit-buffers backing-store
t1
To create a logical T1 controller from each of the specified time slots of the T3 line, use the t1 command in controller configuration mode. To delete the defined logical controller, use the no form of this command.
t1 ds1 controller
no t1 ds1 controller
Syntax Description
Defaults
No default behavior or values.
Command Modes
Controller configuration
Command History
Usage Guidelines
The purpose of this command is to convert the collection of the 28 T1 controllers comprising the T3 controller into individual T1 controllers that the system can use. In other words, the Cisco AS5800 access server cannot pass data until a T1 controller is configured (using the controller command), and you cannot configure a T1 controller until it has been created using the t1 command.
Examples
The following example shows how to configure a logical T1 controller at T1 time slot 1 for the T3 controller located in shelf 1, slot 4, port 0. Note that you have to enter the command from controller configuration mode.
Router(config)# controller t3 1/4/0Router(config-controller)# t1 1 controllerRouter(config-controller)# endRelated Commands
controller
Configures a T1 and other types of controller and enters controller configuration mode.
controller t3
Configures a T3 controller.
t1 bert
To enable or disable a bit error rate tester (BERT) test pattern for a T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 bert command in controller configuration mode. To disable a BERT test pattern, use the no form of this command.
t1 channel bert pattern {0s | 1s | 2^15 | 2^20 | 2^23} interval minutes
no t1 channel bert pattern {0s | 1s | 2^15 | 2^20 | 2^23} interval minutes
Syntax Description
Defaults
No BERT test is performed.
Command Modes
Controller configuration
Command History
Usage Guidelines
The BERT test patterns from the CT3IP are framed test patterns (that is, the test patterns are inserted into the payload of the framed T1 signal).
To view the BERT results, use the show controller t3 or show controller t3 brief EXEC commands. The BERT results include the following information:
•
Type of test pattern selected
•
•
•
•
•
When the T1 channel has a BERT test running, the line state is DOWN. Also, when the BERT test is running and the Status field is Not Sync, the information in the total bit errors field is not valid. When the BERT test is done, the Status field is not relevant.
The t1 bert command is not written to NVRAM because it is only used for testing the T1 channel for a short predefined interval and for avoiding accidentally saving the command, which could cause the interface not to come up the next time the router reboots.
Note
numbering schemes for T1 channels within channelized T3 equipment.Examples
The following example shows how to run a BERT test pattern of all zeros for 30 minutes on T1 channel 6 on the CT3IP in slot 9:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 6 bert pattern 0s interval 30Related Commands
show controllers t3
Displays the hardware and software driver information for a T3 controller.
t1 clock source
To specify where the clock source is obtained for use by each T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 clock source command in controller configuration mode.
t1 channel clock source {internal | line}
Syntax Description
channel
Number between 1 and 28 that indicates the T1 channel.
internal
Specifies that the internal clock source is used. This is the default.
line
Specifies that the network clock source is used.
Defaults
Internal
Command Modes
Controller configuration
Command History
Usage Guidelines
If you do not specify the t1 clock source command, the default clock source of internal is used by all the T1s on the CT3IP.
You can also set the clock source for the CT3IP by using the clock source (CT3IP) controller configuration command.
Note
numbering schemes for T1 channels within channelized T3 equipment.This command does not have a no form.
Examples
The following example shows how to set the clock source to line T1 6 and T1 8 on the CT3IP:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 6 clock source lineRouter(config-controller)# t1 8 clock source lineRelated Commands
clock source (CT3IP)
Specifies where the clock source is obtained for use by the CT3IP in Cisco 7500 series routers.
t1 external
To specify that a T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers is used as an external port so that the T1 channel can be further multiplexed on the Multichannel Interface Processor (MIP) or other multiplexing equipment, use the t1 external command in controller configuration mode. To remove a T1 as an external port, use the no form of this command.
t1 external channel [cablelength feet] [linecode [ami | b8zs]]
no t1 external channel
Syntax Description
Defaults
No external T1 is specified.
The default cable length is 133 feet.
The default line coding is B8ZS.Command Modes
Controller configuration
Command History
Usage Guidelines
The first three T1 channels (1, 2, and 3) of the CT3IP can be broken out to the DSUP-15 connectors on the CPT3IP so that the T1 channel can be further demultiplexed by the MIP on the same router or on another router.
After you configure the external T1 channel, you can continue configuring it as a channelized T1 (also referred to as a fractional T1) from the MIP. All channelized T1 commands might not be applicable to the T1 interface. After you configure the channelized T1 on the MIP, you can continue configuring it as you would a normal serial interface. All serial interface commands might not be applicable to the T1 interface.
The line coding on the T1 channel and the MIP must be the same. Because the default line coding format on the T1 channel is B8ZS and the default line coding on the MIP is AMI, you must change the line coding on the MIP or on the T1 so that they match.
To determine if the external device connected to the external T1 port is configured and cabled correctly before configuring an external port, use the show controllers t3 command and locate the line Ext1... in the display output. The line status can be one of the following:
•
•
•
Note
numbering schemes for T1 channels within channelized T3 equipment.
Note
following ranges: 0 to 133, 134 to 266, 267 to 399, 400 to 533, and 534 to 655. For example,
entering 150 feet uses the 134 to 266 range. If you later change the cable length to 200 feet, there
is no change because 200 is within the 134 to 266 range. However, if you change the cable length to
399, the 267 to 399 range is used. The actual number you enter is stored in the configuration file.Examples
The following example shows how to configure T1 1 on the CT3IP as an external port using AMI line coding and a cable length of 300 feet:
Router(config)# controllers t3 9/0/0Router(config-controller)# t1 external 1 cablelength 300 linecode amiRelated Commands
show controllers t3
Displays the hardware and software driver information for a T3 controller.
t1 fdl ansi
To enable the 1-second transmission of the remote performance reports via the Facility Data Link (FDL) per ANSI T1.403 for a T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 fdl ansi command in controller configuration mode. To disable the performance report, use the no form of this command.
t1 channel fdl ansi
no t1 channel fdl ansi
Syntax Description
Defaults
Disabled
Command Modes
Controller configuration
Command History
Usage Guidelines
The t1 fdl ansi command can be used only if the T1 framing type is Extended Super Frame (ESF).
To display the remote performance report information, use the show controllers t3 remote performance command.
Note
numbering schemes for T1 channels within channelized T3 equipment.Examples
The following example shows how to generate the performance reports for T1 channel 8 on the CT3IP:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 8 fdl ansiRelated Commands
show controllers t3
Displays the hardware and software driver information for a T3 controller.
t1 framing
To specify the type of framing used by the T1 channels on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 framing command in controller configuration mode.
t1 channel framing {esf | sf}
Syntax Description
Defaults
Extended Super Frame (ESF)
Command Modes
Controller configuration
Command History
Usage Guidelines
If you do not specify the t1 framing command, the default ESF is used.
Note
numbering schemes for T1 channels within channelized T3 equipment.This command does not have a no form.
Examples
The following example shows how to set the framing for the T1 6 and T1 8 on the CT3IP to Super Frame:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 6 framing sfRouter(config-controller)# t1 8 framing sft1 linecode
To specify the type of line coding used by the T1 channels on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 linecode command in controller configuration mode.
t1 channel linecode [ami | b8zs]
Syntax Description
Defaults
B8ZS
Command Modes
Controller configuration
Command History
Usage Guidelines
If you do not specify the t1 linecode command, the default B8ZS is used.
AMI Line Coding
If you select ami line coding for the T1 channel, you must also invert the data on the T1 channel by using the invert data interface command. This is required because the T1 channel is bundled into the T3 signal, so there are no local T1 line drivers and receivers associated with it. Therefore, the t1 channel linecode ami command does not modify local line driver settings. Rather, it advises the CT3IP what line code the remote T1 is using. The CT3IP uses this information solely for the purpose of determining whether or not to enable the pulse density enforcer for that T1 channel.
B8ZS Line Coding
When you select b8zs line coding, the pulse density enforcer is disabled. When you select ami line coding, the pulse density enforcer is enabled. To avoid having the pulse density enforcer corrupt data, the T1 channel should be configured for inverted data.
Note
numbering schemes for T1 channels within channelized T3 equipment.Examples
The following example shows how to set the line coding for T1 channel 16 on the CT3IP to AMI:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 16 linecode amiRouter(config-controller)# exitRouter(config)# interface serial 9/0/0:16Router(config-if)# invert dataRelated Commands
invert data
Inverts the data stream.
loopback remote (interface)
Loops packets through a CSU/DSU, over a DS3 link or a channelized T1 link, to the remote CSU/DSU and back.
t1 test
To break out a T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers to the test port for testing, use the t1 test command in controller configuration mode. To remove the T1 channel from the test port, use the no form of this command.
t1 test channel [cablelength feet] [linecode [ami | b8zs]]
no t1 test channel
Syntax Description
Defaults
No test port is configured.
The default cable length is 133 feet.
The default line coding is B8ZS.Command Modes
Controller configuration
Command History
Usage Guidelines
You can use the T1 test port available on the CT3IP to break out any of the 28 T1 channels for testing (for example, 24-hour bit error-rate tester (BERT )testing as is commonly done by telephone companies before a line is brought into service).
The T1 test port is also available as an external port. For more information on configuring an external port, see the t1 external controller configuration command.
To determine if the external device connected to the T1 test port is configured and cabled correctly before configuring a test port, use the show controllers t3 command and locate the line Ext1... in the display output. The line status can be one of the following:
•
•
•
Note
numbering schemes for T1 channels within channelized T3 equipment.
Note
following ranges: 0 to 133, 134 to 266, 267 to 399, 400 to 533, and 534 to 655. For example,
entering 150 feet uses the 134 to 266 range. If you later change the cable length to 200 feet, there is
no change because 200 is within the 134 to 266 range. However, if you change the cable length to
399, the 267 to 399 range is used. The actual number you enter is stored in the configuration file.Examples
The following example shows how to configure T1 6 on the CT3IP as a test port using the default cable length and line coding:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 test 6Related Commands
t1 timeslot
To specify the time slots and data rate used on each T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 timeslot command in controller configuration mode. To remove the configured T1 channel, use the no form of this command.
t1 channel timeslot range [speed {56 | 64}]
no t1 channel timeslot
Syntax Description
Defaults
No time slots are specified for the T1 channel.
The default data rate is 64 kbps.Command Modes
Controller configuration
Command History
Usage Guidelines
You must specify the time slots used by each T1 channel.
Note
Examples
The following example shows how to assign time slots 1 through 24 to T1 1 for full T1 bandwidth usage:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 1 timeslot 1-24The following example shows how to assign time slots 21 to 23 and 26 to 28 and a data rate of 56 kbps to T1 6 for fractional T1 bandwidth usage:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 6 timeslot 21-23,26-28 speed 56t1 yellow
To enable detection and generation of yellow alarms for a T1 channel on the Channelized T3 Interface Processor (CT3IP) in Cisco 7500 series routers, use the t1 yellow command in controller configuration mode. To disable the detection and generation of yellow alarms, use the no form of this command.
t1 channel yellow {detection | generation}
no t1 channel yellow {detection | generation}
Syntax Description
Defaults
Yellow alarms are detected and generated on the T1 channel.
Command Modes
Controller configuration
Command History
Usage Guidelines
If the T1 framing type is super frame (SF), you should consider disabling yellow alarm detection because the yellow alarm can be incorrectly detected with SF framing.
Note
Examples
The following example shows how to disable the yellow alarm detection on T1 channel 6 on the CT3IP:
Router(config)# controller t3 9/0/0Router(config-controller)# t1 6 framing sfRouter(config-controller)# no t1 6 yellow detectiontest aim eeprom
To test the data compression Advanced Interface Module (AIM) after it is installed in the Cisco 2600 series router, use the test aim eeprom command in privileged EXEC mode.
test aim eeprom
Syntax Description
This command has no arguments or keywords.
Defaults
No tests are performed on the data compression AIM card.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command does not have a no form.
Caution
This command is the AIM counterpart of the test pas eeprom command, which performs similar tasks for port modules.
Table 82 shows the questions asked of the user when the test aim eeprom command is entered, and the recommended user responses.
Table 82 Questions and Responses for test aim eeprom Command
There is a danger that you can erase all bytes in the entire EEPROM. Though it is good to have a diagnostic tool that allows you to read and write data, there is a danger that lost data will make the Advanced Interface Module (AIM) card fail.
During your session with the test dialog, you have access to the following commands:
Examples
The following example displays the test aim eeprom command user dialog:
Router# test aim eepromAIM Slot [0]: 0Use NMC93C46 ID EEPROM [y]: yAIM Slot 0 eeprom (? for help)[?]: ?d - dump eeprom contentse - erase all locations (to 1)p - primitive accessq - exit eeprom testz - zero eeprom'c' rules of radix type-in and display apply.AIM Slot 0 eeprom (? for help)[?]:test interface fastethernet
To test the Fast Ethernet interface by causing the interface to ping itself, use the test interface fastethernet command in user EXEC or privileged EXEC mode.
test interface fastethernet number
Syntax Description
Command Modes
User EXEC
Privileged EXECCommand History
Usage Guidelines
This command sends pings from the specified interface to itself. Unlike the ping command, the test interface fastethernet command does not require the use of an IP address.
Examples
The following example shows how to test a Fast Ethernet interface on a Cisco 4500 router:
Router# test interface fastethernet 0Related Commands
test service-module
To perform self-tests on an integrated CSU/DSU serial interface module, such as a 4-wire, 56/64 kbps CSU/DSU, use the test service-module command in privileged EXEC mode.
test service-module interface-type interface-number
Syntax Description
Command Modes
Privileged EXEC
Command History
Usage Guidelines
The following tests are performed on the CSU/DSU:
•
•
•
•
•
These self-tests are also performed at power on.
This command cannot be used if a DTE loopback, line loopback, or remote loopback is in progress.
Data transmission is interrupted for 5 seconds when you issue this command. To view the output of the most recent self-tests, use the show service-module command.
This command does not have a no form.
Examples
The following example shows how to perform a self-test on serial interface 0:
Router# test service-module serial 0SERVICE_MODULE(0): Performing service-module self testSERVICE_MODULE(0): self test finished: PassedRelated Commands
timeslot
To enable framed mode on a serial interface on a G.703 E1 port adapter, an FSIP, or an E1-G.703/G.704 serial port adapter, use the timeslot command in interface configuration mode. To restore the interface to unframed mode, use the no form of this command or set the start slot to 0.
timeslot start-slot stop-slot
no timeslot
Syntax Description
Defaults
The default G.703 E1 interface is not configured for framed mode.
Command Modes
Interface configuration
Command History
10.3
This command was introduced.
11.1 CA
This command was modified to include the E1-G.703/G.704 serial port adapter and Cisco 7200 series routers.
Usage Guidelines
Framed mode allows you to specify a bandwidth for the interface by designating some of the 32 time slots for data and reserving the others for framing (timing). Unframed mode, also known as clear channel, does not reserve any time slots for framing.
This command applies to Cisco 4000, 7000, 7200, and 7500 series routers. G.703 E1 interfaces have two modes of operation, framed and unframed. When in framed mode, the range from start-slot to stop-slot gives the number of 64-kbps slots in use. There are thirty-two 64-kbps slots available.
In framed mode, timeslot 16 is not used for data. To use timeslot 16 for data, use the ts16 interface configuration command.
Examples
The following example shows how to enable framed mode on a serial interface on a G.703 E1 port adapter or an E1-G.703/G.704 port adapter:
Router(config)# interface serial 3/0Router(config-if)# timeslot 1-3Related Commands
Controls the use of timeslot 16 for data on a G.703 E1 interface or on an E1-G703/G.704 serial port adapter.
transmit-buffers backing-store
To buffer short-term traffic bursts that exceed the bandwidth of the output interface, use the transmit-buffers backing-store command in interface configuration mode. To disable this function, use the no form of this command.
transmit-buffers backing-store
no transmit-buffers backing-store
Syntax Description
This command has no arguments or keywords.
Defaults
The default is off, unless weighted fair queueing is enabled on the interface. If weighted fair queueing is enabled on the interface, the transmit-buffers backing-store command is enabled by default.
Command Modes
Interface configuration
Command History
Usage Guidelines
If the transmit-buffers backing-store command is enabled and a full hardware transmit queue is encountered, packets are swapped out of the original memory device (MEMD) into a system buffer in DRAM. If the transmit-buffers backing-store command is not enabled and the output hold queue is full, packets are dropped instead of being copied if a full hardware transmit queue is encountered. In both cases, the original MEMD buffer is freed so that it can be reused for other input packets.
To preserve packet order, the router checks the output hold queue and outputs previously queued packets first.
Examples
The following example shows how to enable the transmit-buffers backing-store command on a FDDI interface:
Router(config)# interface fddi 3/0Router(config-if)# transmit-buffers backing-storeRelated Commands
transmit-clock-internal
To enable the internally generated clock on a serial interface on a Cisco 7200 series or Cisco 7500 series router when a DTE does not return a transmit clock, use the transmit-clock-internal command in interface configuration mode. To disable the internally generated clock, use the no form of this command.
transmit-clock-internal
no transmit-clock-internal
Syntax Description
This command has no arguments or keywords.
Defaults
The internally generated clock is disabled.
Command Modes
Interface configuration
Command History
Examples
The following example shows how to enable the internally generated clock on serial interface 3/0 on a Cisco 7200 series or Cisco 7500 series router:
Router(config)# interface serial 3/0Router(config-if)# transmit-clock-internaltransmitter-delay
To specify a minimum dead-time after transmitting a packet, use the transmitter-delay command in interface configuration mode. To restore the default, use the no form of this command.
transmitter-delay delay
no transmitter-delay
Syntax Description
Defaults
0 flags or microseconds
Command Modes
Interface configuration
Command History
Usage Guidelines
This command is especially useful for serial interfaces that can send back-to-back data packets over serial interfaces faster than some hosts can receive them.
The transmitter delay feature is implemented for the following Token Ring cards: CSC-R16, CSC-R16M, CSC-1R, CSC-2R, and CSC-CTR. For the first four cards, the command syntax is the same as the existing command and specifies the number of microseconds to delay between sending frames that are generated by the router. Transmitter delay for the CSC-CTR uses the same syntax, but specifies a relative time interval to delay between transmission of all frames.
Examples
The following example shows how to specify a delay of 300 microseconds on serial interface 0:
Router(config)# interface serial 0Router(config-if)# transmitter-delay 300ts16
To control the use of time slot 16 for data on a G.703 E1 interface or on an E1-G.703/G.704 serial port adapter, use the ts16 command in interface configuration mode. To restore the default, use the no form of this command.
ts16
no ts16
Syntax Description
This command has no arguments or keywords.
Defaults
Time slot 16 is used for signaling.
Command Modes
Interface configuration
Command History
10.3
This command was introduced.
11.1 CA
This command was implemented on the E1-G.703/G.704 serial port adapter and Cisco 7200 series routers.
Usage Guidelines
This command applies to Cisco 4000, 7000, 7200, and 7500 series routers. By default, time slot 16 is used for signaling. Use this command to configure time slot 16 to be used for data. When in framed mode, in order to get all possible subframes or time slots, you must use the ts16 command.
Examples
The following example shows how to configure time slot 16 to be used for data on a G.703 E1 interface or an E1-G.703/G.704 serial port adapter:
Router(config-if)# ts16Related Commands
Enables framed mode serial interface on a G.703 E1 port adapter, an FSIP, or an E1-G.703/G.704 serial port adapter.
tunnel checksum
To enable encapsulator-to-decapsulator checksumming of packets on a tunnel interface, use the tunnel checksum command in interface configuration mode. To disable checksumming, use the no form of this command.
tunnel checksum
no tunnel checksum
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command currently applies to generic routing encapsulation (GRE) only. Some passenger protocols rely on media checksums to provide data integrity. By default, the tunnel does not guarantee packet integrity. By enabling end-to-end checksums, the routers will drop corrupted packets.
Examples
The following example shows how to enable encapsulator-to-decapsulator checksumming of packets for all protocols on the tunnel interface:
Router(config-if)# tunnel checksumtunnel destination
To specify the destination for a tunnel interface, use the tunnel destination command in interface configuration mode. To remove the destination, use the no form of this command.
tunnel destination {host-name | ip-address}
no tunnel destination
Syntax Description
host-name
Name of the host destination.
ip-address
IP address of the host destination expressed in dotted decimal notation.
Defaults
No tunnel interface destination is specified.
Command Modes
Interface configuration
Command History
Usage Guidelines
You cannot have two tunnels using the same encapsulation mode with exactly the same source and destination address. The work around is to create a loopback interface and source packets off of the loopback interface. Refer to the Cisco IOS AppleTalk, DECnet, ISO CLNS, and Novell IPX Configuration Guide for more information on AppleTalk Cayman tunneling.
Examples
The following example shows how to configure the tunnel destination address for Cayman tunneling:
Router(config)# interface tunnel0Router(config-if)# tunnel source ethernet0Router(config-if)# tunnel destination 10.108.164.19Router(config-if)# tunnel mode caymanThe following example shows how to configure the tunnel destination address for GRE (generic routing encapsulation) tunneling:
Router(config)# interface tunnel0Router(config-if)# appletalk cable-range 4160-4160 4160.19Router(config-if)# appletalk zone EngineeringRouter(config-if)# tunnel source ethernet0Router(config-if)# tunnel destination 10.108.164.19Router(config-if)# tunnel mode gre ipRelated Commands
tunnel key
To enable an ID key for a tunnel interface, use the tunnel key command in interface configuration mode. To remove the ID key, use the no form of this command.
tunnel key key-number
no tunnel key
Syntax Description
Defaults
No tunnel ID keys are enabled.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command currently applies to generic route encapsulation (GRE) only. Tunnel ID keys can be used as a form of weak security to prevent improper configuration or injection of packets from a foreign source.
Note
process-switched. You must configure the no ip mroute-cache command in interface configuration
mode on the interface if an ID key is configured. This note applies only to Cisco IOS Release 12.0 and
earlier releases.
Note
for security purposes.Examples
The following example shows how to set the tunnel ID key to 3:
Router(config-if)# tunnel key 3tunnel mode
To set the encapsulation mode for the tunnel interface, use the tunnel mode command in interface configuration mode. To restore the default mode, use the no form of this command.
tunnel mode {aurp | cayman | dvmrp | eon | gre | gre multipoint | ipip [decapsulate-any] | iptalk | mpls | nos}
no tunnel mode
Syntax Description
Defaults
GRE tunneling
Command Modes
Interface configuration
Command History
Usage Guidelines
Source and Destination Address
You cannot have two tunnels that use the same encapsulation mode with exactly the same source and destination address. The work around is to create a loopback interface and source packets off of the loopback interface.
Cayman Tunneling
Designed by Cayman Systems, Cayman tunneling implements tunneling to enable Cisco routers to interoperate with Cayman GatorBoxes. With Cayman tunneling, you can establish tunnels between two routers or between a Cisco router and a GatorBox. When using Cayman tunneling, you must not configure the tunnel with an AppleTalk network address.
DVMRP
Use DVMRP when a router connects to an mrouted router to run DVMRP over a tunnel. You must configure Protocol Independent Multicast (PIM) and an IP address on a DVMRP tunnel.
GRE with AppleTalk
GRE tunneling can be done between Cisco routers only. When using GRE tunneling for AppleTalk, you configure the tunnel with an AppleTalk network address. Using the AppleTalk network address you can ping the other end of the tunnel to check the connection.
Multipoint GRE
After enabling mGRE tunneling, you can enable the tunnel protection command, which allows you to associate the mGRE tunnel with an IP Security (IPSec) profile. Combining mGRE tunnels and IPSec encryption allows a single mGRE interface to support multiple IPSec tunnels, thereby simplifying the size and complexity of the configuration.
Note
Examples
Cayman Tunneling
The following example shows how to enable Cayman tunneling:
Router(config)# interface tunnel 0Router(config-if)# tunnel source ethernet 0Router(config-if)# tunnel destination 10.108.164.19Router(config-if)# tunnel mode caymanGRE Tunneling
The following example shows how to enable GRE tunneling:
Router(config)# interface tunnel 0Router(config-if)# appletalk cable-range 4160-4160 4160.19Router(config-if)# appletalk zone EngineeringRouter(config-if)# tunnel source ethernet0Router(config-if)# tunnel destination 10.108.164.19Router(config-if)# tunnel mode greMultipoint GRE Tunneling
The following example shows how to enable mGRE tunneling:
interface Tunnel0bandwidth 1000ip address 10.0.0.1 255.255.255.0! Ensures longer packets are fragmented before they are encrypted; otherwise, the ! receiving router would have to do the reassembly.ip mtu 1416! Turns off split horizon on the mGRE tunnel interface; otherwise, EIGRP will not ! advertise routes that are learned via the mGRE interface back out that interface.no ip split-horizon eigrp 1no ip next-hop-self eigrp 1delay 1000! Sets IPSec peer address to Ethernet interface's public address.tunnel source Ethernet0tunnel mode gre multipoint! The following line must match on all nodes that want to use this mGRE tunnel.tunnel key 100000tunnel protection ipsec profile vpnprofRelated Commands
tunnel path-mtu-discovery
To enable Path MTU Discovery (PMTUD) on a generic routing encapsulation (GRE) or IP-in-IP tunnel interface, use the tunnel path-mtu-discovery command in interface configuration mode. To disable PMTUD on a tunnel interface, use the no form of this command.
tunnel path-mtu-discovery [age-timer {aging-mins | infinite} | min-mtu mtu-bytes]
no tunnel path-mtu-discovery
Syntax Description
Defaults
Path MTU Discovery is disabled for a tunnel interface.
Command Modes
Interface configuration
Command History
12.0(5)WC5
This command was introduced.
12.0(7)T3
This command was integrated into Cisco IOS Release 12.0(7)T3.
12.2(13)T
The min-mtu keyword and mtu-bytes argument were added.
Usage Guidelines
When PMTUD (RFC 1191) is enabled on a tunnel interface, the router performs PMTUD processing for the GRE (or IP-in-IP) tunnel IP packets. The router always performs PMTUD processing on the original data IP packets that enter the tunnel. When PMTUD is enabled, no packet fragmentation occurs on the encapsulated packets that travel through the tunnel. Without packet fragmentation, there is a better throughput of TCP connections, and this makes PMTUD a method for maximizing the use of available bandwidth in the network between the endpoints of a tunnel interface.
After PMTUD is enabled, the Don't Fragment (DF) bit of the IP packet header that is forwarded into the tunnel is copied to the IP header of the external IP packets. The external IP packet is the encapsulating IP packet. Adding the DF bit allows the PMTUD mechanism to work on the tunnel path of the tunnel. The tunnel endpoint listens for Internet Control Message Protocol (ICMP) unreachable too-big messages and modifies the IP MTU of the tunnel interface, if required.
When the aging timer is configured, the tunnel code resets the tunnel MTU after the aging timer expires. After the tunnel MTU is reset, a set of full-size packets with the DF bit set is required to trigger the tunnel PMTUD and lower the tunnel MTU. At least two packets are dropped each time the tunnel MTU changes.
When PMTUD is disabled, the DF bit of an external (encapsulated) IP packet is set to zero even if the encapsulated packet has a DF bit set to one.
The min-mtu argument sets a low limit on the MTU that can be learned via the PMTUD process. Any ICMP signaling received specifying an MTU less than the minimum MTU configured will be ignored. This feature can be used to prevent a denial of service attack from any node that can send a specially crafted ICMP message to the router, specifying a very small MTU. For more information, see "Crafted ICMP Messages Can Cause Denial of Service" at the following URL:
http://www.cisco.com/en/US/products/products_security_advisory09186a0080436587.shtml
Note
using PMTUD over firewall connections.PMTUD works only on GRE and IP-in-IP tunnel interfaces.
Use the show interfaces tunnel command to verify the tunnel PMTUD parameters.
Examples
The following example shows how to enable tunnel PMTUD:
Router(config)# interface tunnel 0Router(config-if)# tunnel path-mtu-discoveryRelated Commands
interface
Configures an interface and enters interface configuration mode.
show interfaces tunnel
Displays information about the specified tunnel interface.
tunnel sequence-datagrams
To configure a tunnel interface to drop datagrams that arrive out of order, use the tunnel sequence-datagrams command in interface configuration mode. To disable this function, use the no form of this command.
tunnel sequence-datagrams
no tunnel sequence-datagrams
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
This command currently applies to generic routing encapsulation (GRE) only. This command is useful when carrying passenger protocols that behave poorly when they receive packets out of order (for example, LLC2-based protocols).
Examples
The following example shows how to configure the tunnel to drop datagrams that arrive out of order:
Router(config-if)# tunnel sequence-datagramstunnel source
To set the source address for a tunnel interface, use the tunnel source command in interface configuration mode. To remove the source address, use the no form of this command.
tunnel source {ip-address | interface-type interface-number}
no tunnel source
Syntax Description
Defaults
No tunnel interface source address is set.
Command Modes
Interface configuration
Command History
Usage Guidelines
The source address is either an explicitly defined IP address or the IP address assigned to the specified interface.
You cannot have two tunnels using the same encapsulation mode with exactly the same source and destination address. The workaround is to create a loopback interface and source packets off of the loopback interface.
When using tunnels to Cayman boxes, you must set the tunnel source command to an explicit IP address on the same subnet as the Cayman box, not the tunnel itself.
Examples
The following example shows how to set a tunnel source address for Cayman tunneling:
Router(config)# interface tunnel0Router(config-if)# tunnel source ethernet0Router(config-if)# tunnel destination 131.108.164.19Router(config-if)# tunnel mode caymanThe following example shows how to set a tunnel source address for GRE (generic routing encapsulation) tunneling:
Router(config)# interface tunnel0Router(config-if)# appletalk cable-range 4160-4160 4160.19Router(config-if)# appletalk zone EngineeringRouter(config-if)# tunnel source ethernet0Router(config-if)# tunnel destination 131.108.164.19Router(config-if)# tunnel mode gre ipRelated Commands
tx-queue-limit
To control the number of transmit buffers available to a specified interface on the multiport communications interface (MCI) and serial communications interface (SCI) cards, use the tx-queue-limit command in interface configuration mode.
tx-queue-limit number
Syntax Description
Defaults
Defaults depend on the total transmit buffer pool size and the traffic patterns of all the interfaces on the card. Defaults and specified limits are displayed with the show controllers mci command.
Command Modes
Interface configuration
Command History
Usage Guidelines
This command should be used only under the guidance of a technical support representative.
This command does not have a no form.
Examples
The following example shows how to set the maximum number of transmit buffers on the interface to 5:
Router(config)# interface ethernet 0Router(config-if)# tx-queue-limit 5Related Commands
yellow
To enable generation and detection of yellow alarms, use the yellow command in interface configuration mode.
yellow {generation | detection}
Syntax Description
generation
Enables or disables generation of yellow alarms.
detection
Enables or disables detection of yellow alarms.
Defaults
Yellow alarm generation and detection are enabled.
Command Modes
Interface configuration
Command History
12.0(5)XE
This command was introduced.
12.0(7)XE1
This command was implemented on Cisco 7100 series routers.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
Use this command to generate and detect yellow alarms. If the received signal is lost the yellow alarm can be generated to indicate a frame loss event. Generation of a yellow alarm will ensure that the alarm is sent to the remote end of the link. When the remote end is transmitting a yellow alarm, detection must be enabled to detect the alarm condition.
Examples
The following example shows how to enable generation and detection of yellow alarms on a Cisco 7500 series router:
Router(config)# interface atm 3/1/0Router(config-if)# yellow generationRouter(config-if)# yellow detection
