Console Port, Telnet, and SSH Handling

This chapter covers the following topics:

Console Port Overview for the Cisco ASR 1000 Series Routers

The console port on the Cisco ASR 1000 Series Router is an EIA/TIA-232 asynchronous, serial connection with no flow control and an RJ-45 connector. The console port is used to access the router and is located on the front panel of the Route Processor (RP).

For information on accessing the router using the console port, see the “Accessing the CLI Using a Directly-Connected Console” section on page 3-2 .

Console Port Handling Overview

Users using the console port to access the router are automatically directed to the IOS command-line interface, by default.

If a user is trying to access the router through the console port and sends a break signal (a break signal can be sent by entering Ctrl-C or Ctrl-Shift-6 , or by entering the send break command at the Telnet prompt ) before connecting to the IOS command-line interface, the user is directed into a diagnostic mode by default if the nonRPIOS subpackages can be accessed.

These settings can be changed by configuring a transport map for the console port and applying that transport map to the console interface.

Telnet and SSH Overview for the Cisco ASR 1000 Series Routers

Telnet and Secure Shell (SSH) on the Cisco ASR 1000 Series Routers can be configured and handled like Telnet and SSH on other Cisco platforms. For information on traditional Telnet, see the line command in the Cisco IOS Terminal Services Command Reference guide located at: http://www.cisco.com/en/US/docs/ios/12_2/termserv/command/reference/trflosho.html#wp1029818.

For information on configuring traditional SSH, see the “Configuring Secure Shell” chapter of the Cisco IOS Security Configuration Guide located at: http://www.cisco.com/en/US/docs/ios/12_2/security/configuration/guide/scfssh.html .

The Cisco ASR 1000 Series Routers also introduces persistent Telnet and persistent SSH. Persistent Telnet and persistent SSH allow network administrators to more clearly define the treatment of incoming traffic when users access the router through the Management Ethernet port using Telnet or SSH. Notably, persistent Telnet and persistent SSH provide more robust network access by allowing the router to be configured to be accessible through the Ethernet Management port using Telnet or SSH even when the IOS process has failed.

Persistent Telnet and Persistent SSH Overview

In traditional Cisco routers, accessing the router using Telnet or SSH is not possible in the event of an IOS failure. When Cisco IOS fails on a traditional Cisco router, the only method of accessing the router is through the console port. Similarly, if all active IOS processes have failed on a Cisco ASR 1000 Series Router that is not using persistent Telnet or persistent SSH, the only method of accessing the router is through the console port.

With persistent Telnet and persistent SSH, however, users can configure a transport map that defines the treatment of incoming Telnet or SSH traffic on the Management Ethernet interface.

See the Configuring Persistent Telnet and the Configuring Persistent SSH for information on the various other options that are configurable using persistent Telnet or persistent SSH transport maps.

Configuring a Console Port Transport Map

This task describes how to configure a transport map for a console port interface on the Cisco ASR 1000 Series Router.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. transport-map type console transport-map-name
  4. connection wait [allow interruptible | none ]
  5. exit
  6. transport type console console-line-number input transport-map-name

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure  terminal

Enters global configuration mode.

Step 3

transport-map type console transport-map-name

Example:


Router(config)# transport-map  type  console  consolehandler

Creates and names a transport map for handling console connections, and enter transport map configuration mode.

Step 4

connection wait [allow interruptible | none ]

Example:


Router(config-tmap)# connection  wait  none

Example:

Specifies how a console connection will be handled using this transport map:

  • allow interruptible —The console connection waits for an IOS vty line to become available, and also allows user to enter diagnostic mode by interrupting a console connection waiting for the IOS vty line to become available. This is the default setting.
Note 
Users can interrupt a waiting connection by entering Ctrl-C or Ctrl-Shift-6 .
  • none —The console connection immediately enters diagnostic mode.
Step 5

exit

Example:


Router(config-tmap)# exit

Exits transport map configuration mode to re-enter global configuration mode.

Step 6

transport type console console-line-number input transport-map-name

Example:

Example:


Router(config)# transport  type  console  0  input  consolehandler

Applies the settings defined in the transport map to the console interface.

The transport-map-name for this command must match the transport-map-name defined in the transport-map type console comm and.

Examples

In the following example, a transport map to set console port access policies is created and attached to console port 0: 


Router(config)# transport-map type console consolehandler
Router(config-tmap)# connection wait allow interruptible
Router(config-tmap)# exit
Router(config)# transport type console 0 input consolehandler

Configuring Persistent Telnet

This task describes how to configure persistent Telnet on the Cisco ASR 1000 Series Routers.

Before you begin

For a persistent Telnet connection to access an IOS vty line on the Cisco ASR 1000 Series Router, local login authentication must be configured for the vty line (the login command in line configuration mode). If local login authentication is not configured, users will not be able to access IOS using a Telnet connection into the Management Ethernet interface with an applied transport map.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. transport-map type persistent telnet transport-map-name
  4. connection wait [allow {interruptible }| none {disconnect }]
  5. transport interface gigabitethernet 0
  6. exit
  7. transport type persistent telnet input transport-map-name

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure  terminal

Enters global configuration mode.

Step 3

transport-map type persistent telnet transport-map-name

Example:


Router(config)# transport-map  type  persistent  telnet  telnethandler

Creates and names a transport map for handling persistent Telnet connections, and enters transport map configuration mode.

Step 4

connection wait [allow {interruptible }| none {disconnect }]

Example:


Router(config-tmap)# connection  wait  none

Example:

Specifies how a persistent Telnet connection will be handled using this transport map:

  • allow —The Telnet connection waits for an IOS vty line to become available, and exits the router if interrupted.
  • allow interruptible —The Telnet connection waits for the IOS vty line to become available, and also allows user to enter diagnostic mode by interrupting a Telnet connection waiting for the IOS vty line to become available. This is the default setting.
Note 
Users can interrupt a waiting connection by entering Ctrl-C or Ctrl-Shift-6 .
  • none —The Telnet connection immediately enters diagnostic mode.
  • none disconnect —The Telnet connection does not wait for the IOS vty line and does not enter diagnostic mode, so all Telnet connections are rejected if no vty line is immediately available in IOS.
Step 5

transport interface gigabitethernet 0

Example:


Router(config-tmap)# transport  interface  gigabitethernet  0

Applies the transport map settings to the Management Ethernet interface (interface gigabitethernet 0).

Persistent Telnet can only be applied to the Management Ethernet interface on the Cisco ASR 1000 Series Routers. This step must be taken before applying the transport map to the Management Ethernet interface.

Step 6

exit

Example:


Router(config-tmap)# exit

Exits transport map configuration mode to re-enter global configuration mode.

Step 7

transport type persistent telnet input transport-map-name

Example:

Example:


Router(config)# transport  type  persistent  telnet  input  telnethandler

Applies the settings defined in the transport map to the Management Ethernet interface.

The transport-map-name for this command must match the transport-map-name defined in the transport-map type persistent telnet comm and.

Examples

In the following example, a transport map that will make all Telnet connections wait for an IOS vty line to become available before connecting to the router, while also allowing the user to interrupt the process and enter diagnostic mode, is configured and applied to the Management Ethernet interface (interface gigabitethernet 0).

The transport map is then applied to the interface when the transport type persistent telnet input command is entered to enable persistent Telnet. 


Router(config)# transport-map type persistent telnet telnethandler
Router(config-tmap)# connection wait allow interruptible
Router(config-tmap)# transport interface gigabitethernet 0
Router(config-tmap)# exit
Router(config)# transport type persistent telnet input telnethandler

Configuring Persistent SSH

This task describes how to configure persistent SSH on the Cisco ASR 1000 Series Routers.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. transport-map type persistent ssh transport-map-name
  4. connection wait [allow {interruptible }| none {disconnect }]
  5. rsa keypair-name rsa-keypair-name
  6. authentication-retries number-of-retries
  7. time-out timeout-interval
  8. transport interface gigabitethernet 0
  9. exit
  10. transport type persistent ssh input transport-map-name

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Router> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.
Step 2

configure terminal

Example:


Router# configure  terminal

Enters global configuration mode.

Step 3

transport-map type persistent ssh transport-map-name

Example:


Router(config)# transport-map  type  persistent  ssh  sshhandler

Creates and names a transport map for handling persistent SSH connections, and enters transport map configuration mode.

Step 4

connection wait [allow {interruptible }| none {disconnect }]

Example:


Router(config-tmap)# connection  wait  allow  interruptible

Example:

Specifies how a persistent SSH connection will be handled using this transport map:

  • allow —The SSH connection waits for the vty line to become available, and exits the router if interrupted.
  • allow interruptible —The SSH connection waits for the vty line to become available, and also allows users to enter diagnostic mode by interrupting a SSH connection waiting for the vty line to become available. This is the default setting.
Note 
Users can interrupt a waiting connection by entering Ctrl-C or Ctrl-Shift-6 .
  • none —The SSH connection immediately enters diagnostic mode.
  • none disconnect —The SSH connection does not wait for the vty line from IOS and does not enter diagnostic mode, so all SSH connections are rejected if no vty line is immediately available.
Step 5

rsa keypair-name rsa-keypair-name

Example:


Router(config-tmap)# rsa  keypair-name  sshkeys

Names the RSA keypair to be used for persistent SSH connections.

For persistent SSH connections, the RSA keypair name must be defined using this command in transport map configuration mode. The RSA keypair definitions defined elsewhere on the router, such as through the use of the ip ssh rsa keypair-name command, do not apply to persistent SSH connections.

No rsa-keypair-name is defined by default.

Step 6

authentication-retries number-of-retries

Example:


Router(config-tmap)# authentication-retries  4

(Optional) Specifies the number of authentication retries before dropping the connection.

The default number-of-retries is 3.

Step 7

time-out timeout-interval

Example:


Router(config-tmap)# time-out  30

(Optional) Specifies the SSH time-out interval in seconds.

The default timeout-interval is 120 seconds.

Step 8

transport interface gigabitethernet 0

Example:


Router(config-tmap)# transport  interface  gigabitethernet  0

Applies the transport map settings to the Management Ethernet interface (interface gigabitethernet 0).

Persistent SSH can only be applied to the Management Ethernet interface on the Cisco ASR 1000 Series Routers.

Step 9

exit

Example:


Router(config-tmap)# exit

Exits transport map configuration mode to re-enter global configuration mode.

Step 10

transport type persistent ssh input transport-map-name

Example:

Example:


Router(config)# transport  type  persistent  ssh  input  sshhandler

Applies the settings defined in the transport map to the Management Ethernet interface.

The transport-map-name for this command must match the transport-map-name defined in the transport-map type persistent ssh command .

Examples

In the following example, a transport map that will make all SSH connections wait for the vty line to become active before connecting to the router is configured and applied to the Management Ethernet interface (interface gigabitethernet 0). The RSA keypair is named sshkeys.

This example only uses the commands required to configure persistent SSH. 


Router(config)# transport-map type persistent ssh sshhandler
Router(config-tmap)# connection wait allow
Router(config-tmap)# rsa keypair-name sshkeys
Router(config-tmap)# transport interface gigabitethernet 0

In the following example, a transport map is configured that will apply the following settings to any users attempting to access the Management Ethernet port via SSH:

  • Users using SSH will wait for the vty line to become active, but will enter diagnostic mode if the attempt to access IOS through the vty line is interrupted.
  • The RSA keypair name is sshkeys
  • The connection allows one authentication retry.
  • The banner “ --Waiting for vty line-- ” will appear if the connection is waiting for the vty line to become active.

The transport map is then applied to the interface when the transport type persistent ssh input command is entered to enable persistent SSH: 


Router(config)# transport-map type persistent ssh sshhandler
Router(config-tmap)# connection wait allow interruptible
Router(config-tmap)# rsa keypair-name sshkeys
Router(config-tmap)# authentication-retries 1


Router(config-tmap)#banner wait X
Enter TEXT message.  End with the character 'X'.
--Waiting for vty line--
X
Router(config-tmap)# 
time-out 30
Router(config-tmap)# transport interface gigabitethernet 0
Router(config-tmap)# exit
Router(config)# transport type persistent ssh input sshhandler

Viewing Console Port, SSH, and Telnet Handling Configurations

Use the show transport-map all name transport-map-name | type console persistent ssh telnet ]]] EXEC or privileged EXEC command to view the transport map configurations.

In the following example, a console port, persistent SSH, and persistent Telnet transport are configured on the router and various forms of the show transport-map command are entered to illustrate the various ways the show transport-map command can be entered to gather transport map configuration information. 


Router# show transport-map all
Transport Map:
  Name: consolehandler
  Type: Console Transport
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for the IOS CLI
 
Transport Map:
  Name: sshhandler
  Type: Persistent SSH Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS prompt
  
SSH:
  Timeout: 120
  Authentication retries: 5
  RSA keypair: sshkeys
Transport Map:
  Name: telnethandler
  Type: Persistent Telnet Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS process
  
Transport Map:
  Name: telnethandling1
  Type: Persistent Telnet Transport
Connection:
  Wait option: Wait Allow
Router# show transport-map type console
Transport Map:
  Name: consolehandler
  Type: Console Transport
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for the IOS CLI
  
Router# show transport-map type persistent ssh
Transport Map:
  Name: sshhandler
  Type: Persistent SSH Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS prompt
  
SSH:
  Timeout: 120
  Authentication retries: 5
  RSA keypair: sshkeys
Router# show transport-map type persistent telnet
 
Transport Map:
  Name: telnethandler
  Type: Persistent Telnet Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS process
  
Transport Map:
  Name: telnethandling1
  Type: Persistent Telnet Transport
Connection:
  Wait option: Wait Allow
Router# show transport-map name telnethandler 
Transport Map:
  Name: telnethandler
  Type: Persistent Telnet Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS process
  
Router# show transport-map name consolehandler
Transport Map:
  Name: consolehandler
  Type: Console Transport
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for the IOS CLI
  
Router# show transport-map name sshhandler
Transport Map:
  Name: sshhandler
  Type: Persistent SSH Transport
Interface:
  GigabitEthernet0
Connection:
  Wait option: Wait Allow Interruptable
  Wait banner: 
Waiting for IOS prompt
  
SSH:
  Timeout: 120
  Authentication retries: 5
  RSA keypair: sshkeys
Router#

The show platform software configuration access policy command can be used to view the current configurations for the handling of incoming console port, SSH, and Telnet connections. The output of this command provides the current wait policy for each type of connection, as well as any information on the currently configured banners. 


Router# show platform software configuration access policy 
The current access-policies
Method      : telnet
Rule        : wait
Shell banner: 
Wait banner : 
Method      : ssh
Rule        : wait
Shell banner: 
Wait banner : 
Method      : console
Rule        : wait with interrupt
Shell banner: 
Wait banner :

In the following example, the connection policy and banners are set for a persistent SSH transport map, and the transport map is enabled.

The show platform software configuration access policy output is given both before the new transport map is enabled and after the transport map is enabled so the changes to the SSH configuration are illustrated in the output. 


Router# show platform software configuration access policy
 
The current access-policies
Method      : telnet
Rule        : wait with interrupt

Wait banner : 
Waiting for IOS Process
Method      : ssh
Rule        : wait
Shell banner: 
Wait banner : 
Method      : console
Rule        : wait with interrupt
Shell banner: 
Wait banner : 
Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# transport-map type persistent ssh sshhandler
Router(config-tmap)# connection wait allow interruptible

Router(config-tmap)# rsa keypair-name sshkeys
Router(config-tmap)# transport interface gigabitethernet 0
Router(config-tmap)# exit
Router(config)# transport type persistent ssh input sshhandler 
Router(config)# exit
Router# show platform software configuration access policy
The current access-policies
Method      : telnet
Rule        : wait with interrupt

Wait banner : 
Waiting for IOS process
Method      : ssh
Rule        : wait with interrupt

Wait banner : 
Waiting for IOS
Method      : console
Rule        : wait with interrupt
Shell banner: 
Wait banner :

Important Notes and Restrictions

The important notes and restriction pertaining to the console port, SSH, and telnet handling include:

  • The Telnet and SSH settings made in the transport map override any other Telnet or SSH settings when the transport map is applied to the Management Ethernet interface.
  • Only local usernames and passwords can be used to authenticate users entering a Management Ethernet interface. AAA authentication is not available for users accessing the router through a Management Ethernet interface using persistent Telnet or persistent SSH.
  • Applying a transport map to a Management Ethernet interface with active Telnet or SSH sessions can disconnect the active sessions. Removing a transport map from an interface, however, does not disconnect any active Telnet or SSH sessions.