Secure Cisco Discovery Protocol

The Cisco Discovery Protocol does not possess inherent security mechanisms and is vulnerable to attacks. The Secure Cisco Discovery Protocol feature allows users to select the type, length, value (TLV) fields that are sent on a particular interface to filter information sent through Cisco Discovery Protocol packets.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

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.

Prerequisites for Secure Cisco Discovery Protocol

The Cisco software image must support basic Cisco Discovery Protocol functions.

Restrictions for Secure Cisco Discovery Protocol

Blocking the type, length, value (TLV) fields on one device can affect the functionality of clients on other devices where Cisco Discovery Protocol packets with blocked TLV fields are received because different clients use different TLV fields.

Information About Secure Cisco Discovery Protocol

Secure Cisco Discovery Protocol

The Cisco Discovery Protocol does not possess inherent security mechanisms and is vulnerable to attacks. The Secure Cisco Discovery Protocol feature provides security by allowing users to select the type, length, value (TLV) fields that are sent on an interface to filter the fields in Cisco Discovery Protocol packets.

This feature supports the following functions:

  • TLV lists can be configured globally and also at the interface level, but only one TLV fields list can be configured globally.

  • A TLV list configured on an interface is given a higher precedence.

  • All TLVs except the Device-ID TLV and the Application TLV can be blocked.

  • Information about the Cisco Discovery Protocol TLV list configured on an interface is stored in each Cisco Discovery Protocol interface subblock.

  • All TLVs are blocked on the sending side.

  • The cdp tlv-list and cdp filter-tlv-list commands are required to configure a Cisco Discovery Protocol list and apply the list globally or on an interface.

  • The show cdp tlv-list and show cdp interface commands display information about the TLV list.

Supported Type, Length, Value Fields

Table 1 Supported TLV fields
Related command in TLV list configuration mode TLV Fields Description

address

Address TLV

Contains a list of device network-layer addresses. If a device uses Simple Network Management Protocol (SNMP), the first address is an address at which the device receives SNMP messages.

The device may advertise all of its addresses and may optionally advertise one or more loopback IP addresses.

capability

Capability TLV

Identifies the device type. The device type indicates the functional capability of the device, for example, a switch.

cos

Class of service TLV

Describes the Layer 2 class of service (CoS) value in a Cisco Discovery Protocol packet. All Cisco Discovery Protocol packets received on an untrusted port are marked with a CoS value by a switching device that cannot classify individual packets.

This TLV is used only in a Cisco Discovery Protocol packet that contains an Extended Trust TLV, which indicates the absence of extended trust with a CoS TLV that is one byte in length.

default

Default

Specifies the default state of the configuration.

duplex

Duplex TLV

Allows devices to recognize if a point-to-point Ethernet interface is running in full-duplex or in half-duplex mode. Network problems are caused if two ends of a link are in different modes.

The TLV value is one byte in length with its least significant bit indicating the mode. A 1 indicates full-duplex and a 0’indicates half-duplex.

exit

Exit

Exits current configuration.

ext-port-id

External Port Id TLV

Identifies the physical connector port on which a Cisco Discovery Protocol packet is transmitted.

This TLV is used in devices with optical ports in which signals from multiple hardware interfaces are multiplexed through a single physical port.

The value of this TLV must be the same as the MIB object ifName for the ifTable entry for the external port.

hello-protocol

Protocol-Hello TLV

Specifies that a particular protocol has asked Cisco Discovery Protocol to piggyback its “hello” messages within transmitted Cisco Discovery Protocol packets.

The value of this TLV protocol is greater than or equal to 5 and lesser than or equal to 32 bytes. The first 5 bytes are the protocol’s 5-byte Subnetwork Access Protocol (SNAP) value, which contains three bytes of organizationally unique identifier (OUI) followed by two bytes of protocol ID.

A Cisco Discovery Protocol packet may contain multiple protocol-hello TLVs, each for a different protocol.

ip-prefix

IP Network Prefix TLV

Describes a list of stub network prefixes to which the sending stub device can forward IP packets. These packets are used by On-Demand Routing (ODR).

Each network prefix is formatted as a 4-byte IP address followed by a 1-byte network mask length. Thus, the length of the value sent by a stub device is a multiple of 5 bytes.

location

Location TLV

Delivers location-based information to endpoint devices through switches, routers, or access devices using the Cisco Discovery Protocol. The Location TLV can send the following types of information:

  • Custom location—Provides the location and attributes of the endpoint device.

  • Civic location information—Provides the civic address information and postal information; for example, street address, road name, and postal community information.

  • ELIN location information—Provides the location information of a caller. The location is determined by the emergency location identifier number (ELIN), which is a phone number that routes an emergency call to the local public safety answering point (PSAP). The PSAP uses this information to call back.

  • Geo spatial location information—Provides the longitude, latitude, and altitude information of the endpoint device.

You must configure the location TLV on the device before Cisco Discovery Protocol can deliver location-based information to the endpoint devices.

location-server

Location-server TLV

Provides a mechanism for location servers to transfer the required information to the neighbor devices.

mgmt-address

Management Address TLV

Contains a list of network layer addresses encoded similarly to the Address TLV.

This TLV contains a list of all the addresses at which the device accepts SNMP messages.

native-vlan

Native VLAN TLV

Indicates the Inter-Switch Link (ISL) number of the native interface VLAN on which the Cisco Discovery Protocol packet is sent, as well as whether the VLAN is enabled on the link and whether the link is a trunk or a host/edge port.

platform

Platform TLV

Describes the hardware platform of the device. Encoded as an ASCII character string. The TLV length determines the length of the string.

port-id

Port-ID TLV

Identifies the port on which the Cisco Discovery Protocol packet is sent. This is encoded as an ASCII character string.

The value of this TLV is the same as the MIB object ifName for the ifTable entry on which the Cisco Discovery Protocol packet is sent.

power -available

Power Available TLV

Specifies the information transmitted by all switch interfaces. This information permits a device that needs power to negotiate and select an appropriate power setting. The Power Available TLV includes four fields:

  • Request-ID field

  • Available-Power field

  • Power-Management-ID field

  • Management-Power-Level field

powernet

Energywise TLV

Discovers neighbor devices, communicates and negotiates power-related parameters with Cisco end devices such as an IP phone and access point.

trust

Extended Trust TLV

Specifies that the trust from the larger switch port is extended to other (external) ports of the simple switching device without explicitly configuring the trust on the simple switching device.

Extending trust allows a network administrator to trust a host/server to mark the packets and the port on which this host/server is connected. Packets received on a trusted port are not marked again.

The TLV value is one byte in length with its least significant bit indicating the trust mode. A 1 indicates extended trust and a 0 indicates the absence of extended trust. All other bits of the TLV value should be set to 0 on transmission and ignored on receipt.

A Cisco Discovery Protocol packet without this TLV indicates the absence of extended trust.

version

Version TLV

Contains information about the Cisco software image version the device is running. This is in the form of a character string. The TLV length determines the length of the string. This information is displayed in the output of the show version command.

vtp-mgmt-domain

VTP Management Domain TLV

Specifies the name of the VLAN Trunking Protocol (VTP) management domain for a device running the VTP on the particular interface on which the Cisco Discovery Protocol packet is sent.

The length of this TLV determines the length of the VTP management domain name. A length of zero indicates that a device is running VTP but has no management domain name assigned to it.

vvid

Appliance VLAN-ID TLV

Indicates the setting of the local configuration when a local 802.1Q interface has been configured to send and receive VoIP and related packets on a particular VLAN.

Devices receiving this TLV may adjust their configuration to match this setting.


Note

The Address TLV and Device ID TLV are mandatory TLVs and they cannot be blocked. Hence, they are not available in the Cisco software image for user configuration.

How to Configure Secure Cisco Discovery Protocol

Configuring a TLV List and Adding TLVs to the List

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    cdp tlv-list tlv-list-name

    4.    ip-prefix

    5.    hello-protocol

    6.    end

    7.    show cdp tlv-list tlv-list-name


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 cdp tlv-list tlv-list-name


    Example:
    Device(config)# cdp tlv-list group1
     

    Configures the type, length, value (TLV) list that allows users to select TLVs and enters TLV list configuration mode.

     
    Step 4 ip-prefix


    Example:
    Device(config-tlv-list)# ip-prefix
     

    Adds the IP prefix TLV to the TLV list.

     
    Step 5 hello-protocol


    Example:
    Device(config-tlv-list)# hello-protocol
     

    Adds the Protocol-Hello TLV to the TLV list.

    Note   

    In TLV list configuration mode, enter the CLI help (?) command to view a list of TLVs that are not added to the TLV list.

     
    Step 6 end


    Example:
    Device(config-tlv-list)# end
     

    Exits TLV list configuration mode and returns to privileged EXEC mode.

     
    Step 7 show cdp tlv-list tlv-list-name


    Example:
    Device# show cdp tlv-list group1
     

    Displays information about the TLVs in a TLV list.

     

    Applying TLV List Configurations at the Interface Level

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    cdp filter-tlv-list tlv-list-name

      5.    end

      6.    show cdp tlv-list tlv-list-name


    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 interface type number


      Example:
      Device# interface ethernet 0/0
       

      Specifies an interface type and enters interface configuration mode.

       
      Step 4 cdp filter-tlv-list tlv-list-name


      Example:
      Device(config-if)# cdp filter-tlv-list group1
       

      Applies a TLV list on an interface.

       
      Step 5 end


      Example:
      Device(config-if)# end
       

      Exits interface configuration mode and returns to privileged EXEC mode.

       
      Step 6 show cdp tlv-list tlv-list-name


      Example:
      Device# show cdp tlv-list group1
       

      Displays information about the TLVs in a TLV list.

       

      Applying TLV List Configurations at the Global Level

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    cdp filter-tlv-list tlv-list-name

        4.    end

        5.    show cdp tlv-list tlv-list-name


      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 cdp filter-tlv-list tlv-list-name


        Example:
        Device(config)# cdp filter-tlv-list group1
         

        Applies a TLV list globally.

         
        Step 4 end


        Example:
        Device(config)# end
         

        Exits global configuration mode and returns to the privileged EXEC mode.

         
        Step 5 show cdp tlv-list tlv-list-name


        Example:
        Device# show cdp tlv-list group1
         

        Displays information about the TLVs in a TLV list.

         

        Configuration Examples for Secure Cisco Discovery Protocol

        Example: Configuring a TLV List and Adding TLVs to the List

        The following example shows how to create a type, length, value (TLV) list, group1 and add TLVs to the list: 
        Device> enable
Device# configure terminal
Device(config)# cdp tlv-list group1
Device(config-tlv-list)# ip-prefix
Device(config-tlv-list)# hello-protocol
Device(config-tlv-list)# trust
Device(config-tlv-list)# capability

        The following example shows how to create a TLV list, group2 and add TLVs to the list: 
        Device(config)# cdp tlv-list group2
Device(config-tlv-list)# address
Device(config-tlv-list)# duplex
Device(config-tlv-list)# capability
Device(config-tlv-list)# end

        The following example shows how to view the TLV lists and the TLVs that are added to the lists: 
        Device# show cdp tlv-list group1

Tlv-list : group1
Capability  Hello-protocol  Ip-prefix  Trust

Device# show cdp tlv-list group2

Tlv-list : group2
Address  Capability  Duplex

Device# show cdp tlv-list *

Tlv-list : group1
Capability  Hello-protocol  Ip-prefix  Trust

Tlv-list : group2
Address  Capability  Duplex

        Note

        • The show cdp tlv-list * command displays all configured Cisco Discovery Protocol TLV lists.

        Example: Applying TLV List Configurations at Interface Level

        The show cdp interface command displays Cisco Discovery Protocol TLV lists on all interfaces.

        The following example shows how to apply Cisco Discovery Protocol type, length, value (TLV) lists on an interface: 
        Device> enable
Device# configure terminal
Device(config)# interface ethernet 0/0
Device(config-if)# cdp filter-tlv-list group1
03:22:15: %CDP-6-TLV_LIST_INTERFACE: Tlv-list group1 applied on 
interface Ethernet0/0
Device(config-if)# exit
Device(config)# interface ethernet 0/1
Device(config-if)# cdp filter-tlv-list group2
03:22:45: %CDP-6-TLV_LIST_INTERFACE: Tlv-list group2 applied on 
interface Ethernet0/1
Device(config-if)# end
Device# show cdp tlv-list group1

Tlv-list : group1
Capability  Hello-protocol  Ip-prefix  Trust
Applied on:
Et0/0

Device# show cdp interface ethernet0/0

Ethernet0/0 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group1

Device# show cdp interface ethernet0/1

Ethernet0/1 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group2

Device# show cdp interface

Ethernet0/0 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group1
Ethernet0/1 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group2
.
.
.

        Example: Applying TLV List Configurations Globally

        The following example shows how to globally apply a Cisco Discovery Protocol type, length, value (TLV) list:
        Device> enable
Device# configure terminal
Device(config)# cdp filter-tlv-list group1
03:28:44: %CDP-6-TLV_LIST_GLOBALLY: Tlv-list group1 applied globally on all
interfaces.
Device(config)# end
Device# show cdp interface

Ethernet0/0 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group1
Ethernet0/1 is up, line protocol is up
  Encapsulation ARPA
  Sending CDP packets every 60 seconds
  Holdtime is 180 seconds
  Tlv-list applied : group2
.
.
.

        Note

        The show cdp interface command displays Cisco Discovery Protocol TLV lists on all interfaces.

        Additional References for Secure Cisco Discovery Protocol

        Related Documents

        Related Topic

        Document Title

        Cisco IOS commands

        Cisco IOS Master Command List, All Releases

        Cisco Discovery Protocol commands

        Cisco IOS Cisco Discovery Protocol Command Reference

        SNMP configuration tasks

        Configuring SNMP Support

        On-Demand Routing configuration tasks

        Configuring On-Demand Routing

        Standards and RFCs

        Standard/RFC

        Title

        IEEE 802.1Q

        802.1Q—Virtual LANs

        MIBs

        MIB

        MIBs Link

        CISCO-CDP MIB

        To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

        http:/​/​www.cisco.com/​go/​mibs

        Technical Assistance

        Description

        Link

        The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

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

        Feature Information for Secure Cisco Discovery Protocol

        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 2 Feature Information for Secure Cisco Discovery Protocol

        Feature Name

        Releases

        Feature Information

        Secure Cisco Discovery Protocol

        15.4(1)T

        The Secure Cisco Discovery Protocol feature allows you to select what information is sent in Cisco Discovery Protocol packets and block sensitive information.

        The following commands were introduced or modified: cdp filter-tlv-list, cdp tlv-list, show cdp interface, show cdp tlv-list.