DHCP Zero Touch

The Cisco Dynamic Host Control Protocol (DHCP) Zero Touch feature enables a device to retrieve configuration files from the remote DHCP server during initial deployment with no end-user intervention.

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Information About DHCP Zero Touch

DHCP Zero Touch Overview

The DHCP Zero Touch feature enables a device to retrieve configuration files from the remote Dynamic Host Configuration Protocol (DHCP) server during the initial device deployment without end-user intervention. You need a bootstrap configuration to communicate between the device and the remote server. The bootstrap configuration provides specific information about a device. This bootstrap configuration can be pre-installed on the device or can be retrieved from the DHCP server. The DHCP Zero Touch feature introduces another method of retrieving bootstrap configuration information: using the DHCP Option 43 message. To accommodate situations where devices cannot have a pre-installed bootstrap configuration, a deployment model that uses DHCP Option 43 messages is used. Cisco recommends using DHCP Option 43 messages based on RFC 2132. You can use the DHCP Option 43 message to provide vendor-specific information in the form of ASCII codes to the DHCP server.

The DHCP Option 43 message supplies the necessary information that is normally provided in the bootstrap configuration to the DHCP client. When the DHCP client issues a DHCP IP address request to the DHCP server, the DHCP server sends out the IP address and a DHCP Option 43 message, if the DHCP Option 43 message is preconfigured on the DHCP server. Within this DHCP Option 43 message, predefined parameterized commands are provided to the DHCP client. A timer for three minutes is set. After the timeout, if the file download is successful, the process is complete. If the file download fails, check the generated DHCP Option 43 message and correct any problems. Power cycle the device to retry the DHCP Option 43 message process.

Initiating DHCP Option 43 Messages with WSMA

At router system initiation time, there are two ways to initiate the DHCP IP address request to enable the DHCP Option 43 message to be sent to the device:

  1. If the device is enabled with startup configuration, zero touch deployment can be enabled by using the ip address dhcp and the wsma dhcp configuration commands.

  2. If the device is not enabled with startup configuration, the Autoinstall feature automatically initializes the ip address dhcp configuration command, which enables the zero touch deployment. For more information about the Autoinstall feature, see the “Overview—Basic Configuration of a Cisco Networking Device” module in the Configuration Fundamentals Configuration Guide.

WSMA Parameterized Commands

The values configured using the wsma id, wsma agent, and wsma profile initiator commands are used as parameters to construct the DHCP Option 43 message to enable zero touch deployment (ZTD). The DHCP Option 43 message provides these predefined parameterized commands to the Dynamic Host Control Protocol (DHCP) client, which enables the client to decode and read the messages sent by the DHCP server.

Constructing a DHCP Option 43 Message

The DHCP Option 43 message is presented in the type/value (TV) format. The DHCP Option 43 message is used by clients and servers to exchange vendor-specific information. When you use the vendor-specific option (Option 43), you must specify the data using hexadecimal ASCII values. For more information on the option command, refer to the Cisco IOS IP Addressing Services Command Reference.


Note

The maximum DHCP Option 43 size is 2500 bytes.

Following are the parameters used by the WSMA to construct the DHCP Option 43 message to enable ZTD: 

<DHCP-typecode><feature-opcode><version><debug-option>;<arglist>
Table 1 Parameters of DHCP Option 43 Message

Parameter

Description

DHCP-typecode

Specifies the DHCP suboption type. The DHCP suboption type for WSMA is 4.

feature-opcode

There are two types of feature operation codes—Active (A) and Passive (P). The feature operation code for WSMA is Active (A) template. This code initiates a connection to the management server and sends a hello message to it. If the management server cannot be reached, the device keeps trying to connect until it gets through.

version

Indicates the version of template to be used by the WSMA.

debug-option

Indicates if debug messages have to be generated during the processing of the DHCP Option 43 messages. Debug OFF is recommended for normal processing and debug ON can be used for debugging the processing of DHCP Option 43 messages. The following are the two debug options:

  • D—debug option is ON

  • N—debug option is OFF

;

Delimiter used to separate the parameters.

arglist

List of named arguments for the command, separated by a semicolon. To use the default value for an argument, do not specify values for that parameter.

Letter codes are used to identify the arguments. Name and value pairs can be listed in any order and are delimited by a semicolon.

The table below lists the arguments for configuring the WSMA ID and the initiator profile parameters used for configuring the WSMA configuration agent.

Table 2 Argument Lists for WSMA Active Template A (WSMA Indicators)

Parameter

Letter Code

Values

Parameter to CLI Mapping: Sample Letter Code

Parameter to CLI Mapping: Sample CLI Mapping

WSMA ID

A

(Optional) Indicates the WSMA ID. The default is hostname.

1—Indicates a custom string to be used.

2—Indicates the MAC address of the interface used.

3—Indicates the hardware serial number to be used.

4—Indicates Unified Display Interface (UDI). 

A1881-ap 
A4
 
Device(config)# wsma 
id string 881-ap
Device(config)# wsma 
id udi

Remote server IP ADDR

I

(Required) Indicates an IPv4 or IPv6 address or hostname. Set the DNS-server option for DHCP, if you use hostname. 

I10.10.10.1-

Device(config-wsma-init)#
transport tls 
10.10.10.1

Remote server part

J

(Optional) Indicates the remote server part. The default port is 13000. 

J10000
 
Device(config-wsma-init)# 
transport tls 
10.10.10.1.10090

Transport protocol for WSMA initiator

K

(Required) Indicates the transport protocol for WSMA initiator.

1—TLS

2—SSH

3—HTTPS

4—HTTP 

K1
 
Device(config)# 
wsma profile intiator
 zero-touch

Device(config-wsma-init)# 
transport tls 
10.10.10.1 10090

Encapsulation

B

(Optional) Indicates the encapsulation of a WSMA profile. The default is Simple Object Access Protocol (SOAP) 11.

1—SOAP 11

2—SOAP 12 

B
 
Device(config-wsma-listener)# 
encap soap12

Max message C

C

(Optional) Indicates the maximum size limit for incoming messages. The default is 50 KB.

Numeric string between 1 KB and 2000 KB. 

C
 
Device(config-wsma-listener)#
 max-message 50

CA Server IP address

L

(Required) Indicates the IP address or hostname of certificate authority (CA) server for the Transport Layer Security (TLS) or Secure HTTP (HTTPS) protocol. 

L
 
Device(ca-trustpoint)# 
enrollment url 
http://10.1.43.216:80

Source interface

M

Indicates the source interface name. It is applicable for the TLS protocol. 

M11011
 
Device(config-wsma-initiator)#
transport tls name1 
11011 source 
fastethernet 0/1

User name

N

(Required) Specifies the Username for SSH protocol. It is not applicable for the TLS protocol. 

N11011
 
Device(config-wsma-initiator)#
transport ssh user1 
11011 path remote-cmd-text 
user username password

User password

O

(Required) Specifies the password for accessing the SSH protocol. It is not applicable for the TLS protocol. 

O11011
 
Device(config-wsma-initiator)#
transport ssh user1 
11011 path 
remote-cmd-text user 
username password

Connect string/path

P

(Required) Specifies a connect string command for SSH, or the path for HTTPS and HTTP. It is not applicable for the TLS protocol. 

P11011
 
Device(config-wsma-initiator)#
transport https user1
11011 path remote-cmd-text 
user username password

idle-timeout

Q

(Optional) Specifies the timeout value in minutes. The default is 1. 

Q30
 
Device(config-atm-vc)#
idle-timeout 30

domain-name

R

(Optional) Specifies the name of the domain that hosts the DHCP client. This parameter is applicable for the TLS protocol. 

example.com
 
Device(config)#
ip domain list 
example.com

fingerprint

T

(Optional) Specifies a fingerprint that can be matched against the fingerprint of a certification authority (CA) certificate during authentication. It is applicable for the TLS protocol. 

T96E50E2C
126CC3149
0B319E3BFD
40FE663DB5
664
 
Device(ca-trustpoint)# 
fingerprint 96E50E2C126CC3149
0B319E3BFD4
0FE663DB5664

fqdn

U

(Optional) Specifies a hostname and a domain name. It is applicable for the TLS protocol. 

example.com
 
Device(ca-trustpoint)#
fqdn dp-7214.examplecom

Keepalive-interval

V

(Optional) Specifies the number of keepalive intervals. 

V600
 
Device(config-wsma-initiator)#
keepalive 600

Keepalive-retries

W

(Optional) Specifies the number of keepalive retries. 

W5
 
Device(config-wsma-initiator)#
keepalive 600 retries 5

Crypto cmd wait time

X

(Optional) Specifies the time taken in seconds before a crypto command is executed.

1—15 seconds

2—30 seconds

3—45 seconds

4—60 seconds

5—120 seconds

6—180 seconds 

X
 
NA

Default gateway

Y

Specifies the system's default gateway that needs to be configured. 

Y0.0.0.0
 
Device(config)# 
ip route 
0.0.0.0 0.0.0.0 
10.1.43.254

Note

Backup servers are not available. Type 6 encryption cannot be provided for zero touch due to additional initial configuration required on the Cisco device. The device tries to reconnect every 60 seconds for 15 minutes. If the server cannot be reached within the specified time, the device accepts reconfiguration via the DHCP Option 43 message.

How to Configure DHCP Zero Touch

Enabling WSMA to Receive a DHCP Option 43 Message

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    wsma dhcp

    4.    exit


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 wsma dhcp


    Example:
    Device(config)# wsma dhcp
     

    Enables WSMA with permission to process an incoming DHCP Option 43 message.

     
    Step 4 exit


    Example:
    Device(config)# exit
     

    Exits global configuration mode.

     

    Enabling CNS to Receive a DHCP Option 43 Message

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    cns dhcp

      4.    exit


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3 cns dhcp


      Example:
      Device(config)# cns dhcp
       

      Enables CNS with permission to process an incoming DHCP Option 43 message.

       
      Step 4 exit


      Example:
      Device(config)# exit
       

      Exits global configuration mode.

       

      Configuration Examples for DHCP Zero Touch

      Example: Using DHCP Option 43 to Retrieve the Initial Configuration File

      Example 1

      In this example, in response to a DHCP IP address request sent by the Dynamic Host Control Protocol (DHCP) client, the DHCP server sends an Option 43 message such as 4A1N;I10.10.10.1;K1 to the DHCP client. The DHCP client forwards the Option 43 message to the Web Services Management Agent (WSMA). The WSMA verifies if the Option 43 message is allowed to process. Option 43 messages are allowed to process by the WSMA if the wsma dhcp command is enabled on the WSMA.

      The parameters for the 4A1N;I10.10.10.1;K1 message are mapped as follows:

      • 4—DHCP-typecode for WSMA

      • A—Active template code

      • 1—Version number of the Active template

      • N—Debug option, which is OFF

      • ;—Delimiter before the argument list

      • I10.10.10.1—IP address of the management server

      • K1—Transport protocol for the initiator used in Transport Layer Security (TLS)

      The WSMA constructs the following commands and sends them to the remote management server to request the initial configuration file. A timer is set for five minutes. 

      Device(config)# wsma agent config profile zero-touch
Device(config)# wsma profile initiator zero-touch
Device(config-wsma-initiator)# transport tls 10.10.10.1
Device(config-wsma-initiator)# no wsse authorization level 15

      The initial configuration file that is downloaded is checked. If the file download is successful, the process is complete.

      Example 2

      In this example, in response to a DHCP IP address request sent by the DHCP client, the DHCP server sends an Option 43 message such as 4A1N;A1881-ap;D10.10.10.1;K1 to the DHCP client. The DHCP client forwards the Option 43 message to the WSMA. The WSMA verifies if the Option 43 message is allowed to process. Option 43 messages are allowed to process by the WSMA if the wsma dhcp command is enabled on the WSMA.

      The parameters for the A1881-ap;D10.10.10.1;K1 message are mapped as follows:

      • 4—DHCP-typecode for WSMA

      • A—Active template code

      • 1—Version number of the Active template

      • N—Debug option, which is OFF

      • ;—Delimiter before the argument list

      • 881-ap—Active template string values

      • D10.10.10.1—IP address of the management server

      • K1—Transport protocol for initiator used in TLS

      The WSMA constructs the following commands and sends them to the remote management server to request the initial configuration file. A timer is set for five minutes. 

      Device(config)# wsma agent config profile zero-touch
Device(config)# wsma profile initiator zero-touch
Device(config-wsma-initiator)# transport tls 10.10.10.1
Device(config-wsma-initiator)# no wsse authorization level 15

      Feature Information for DHCP Zero Touch

      The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

      Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.
      Table 3 Feature Information for DHCP Zero Touch

      Feature Name

      Releases

      Feature Information

      DHCP Zero Touch

      The DHCP Zero Touch feature allows you to configure the attributes of a device at initial deployment from a DHCP server. DHCP option 43 allows hands-free zero touch deployments.

      The following commands were introduced or modified: wsma dhcp, cns dhcp.

      Additional References

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Commands List, All Releases

      WSMA commands

      Cisco IOS Web Services Management Agent Command Reference

      IP access lists

      Security Configuration Guide: Access Control Lists in the Securing the Data Plan Configuration Guide Library

      Public Key Infrastructure

      Public Key Infrastructure Configuration Guide in the Secure Connectivity Configuration Guide Library

      Secure Shell and Secure Shell Version 2

      Secure Shell Configuration Guide in the Securing User Services Configuration Guide Library

      Security and IP access lists commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

      Cisco IOS Security Command Reference

      RFCs

      RFC

      Title

      RFC 2132

      DHCP Options and BOOTP Vendor Extensions

      RFC 2246

      The TLS Protocol Version 1.0

      RFC 4251

      The Secure Shell (SSH) Protocol Architecture

      RFC 4252

      The Secure Shell (SSH) Authentication Protocol

      Technical Assistance

      Description

      Link

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      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html