Cisco IOS XR IP Addresses and Services Configuration Guide for the Cisco XR 12000 Series Router, Release 4.3.x
Implementing the Dynamic Host Configuration Protocol
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Implementing the Dynamic Host Configuration Protocol

Contents

Implementing the Dynamic Host Configuration Protocol

This module describes the concepts and tasks you will use to configure Dynamic Host Configuration Protocol (DHCP).

Feature History for Implementing the Dynamic Host Configuration Protocol

Release

Modification

Release 3.2

This feature was introduced.

Release 3.4.0

The DHCP IPv6 Information Pool configuration procedure was added and DCHP relay information description was updated.

Release 3.7.0

The DHCP CLI was modified.

Prerequisites for Configuring DHCP Relay Agent

The following prerequisites are required to configure a DHCP relay agent:

  • You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
  • A configured and running DHCP client and DHCP server
  • Connectivity between the relay agent and DCHP server

Information About DHCP Relay Agent

A DHCP relay agent is a host that forwards DHCP packets between clients and servers that do not reside on a shared physical subnet. Relay agent forwarding is distinct from the normal forwarding of an IP router where IP datagrams are switched between networks transparently.

DHCP clients use User Datagram Protocol (UDP) broadcasts to send DHCPDISCOVER messages when they lack information about the network to which they belong.

If a client is on a network segment that does not include a server, a relay agent is needed on that network segment to ensure that DHCP packets reach the servers on another network segment. UDP broadcast packets are not forwarded, because most routers are not configured to forward broadcast traffic. You can configure a DHCP relay profile and configure one or more helper addresses in it. You can assign the profile to an interface or a VRF.

Figure 1 demonstrates the process. The DHCP client broadcasts a request for an IP address and additional configuration parameters on its local LAN. Acting as a DHCP relay agent, Router B picks up the broadcast, changes the destination address to the DHCP server's address and sends the message out on another interface. The relay agent inserts the IP address of the interface, on which the relay profile into the gateway address (giaddr) field of the DHCP packet, which enables the DHCP server to determine which subnet should receive the offer and identify the appropriate IP address range. The relay agent unicasts the messages to the server address, in this case 172.16.1.2 (which is specified by the helper address in the relay profile).

Figure 1. Forwarding UDP Broadcasts to a DHCP Server Using a Helper Address

How to Configure and Enable DHCP Relay Agent

This section contains the following tasks:

Configuring and Enabling the DHCP Relay Agent

Configuring a DHCP Relay Profile

This task describes how to configure and enable the DHCP relay agent.

SUMMARY STEPS

    1.    configure

    2.    dhcp ipv4

    3.    profile profile-name relay

    4.    helper-address [vrf vrf- name ] address

    5.    Use one of these commands:

    • end
    • commit


DETAILED STEPS
      Command or Action Purpose
    Step 1 configure


    Example:
    RP/0/0/CPU0:router# configure
     

    Enters global configuration mode.

     
    Step 2 dhcp ipv4


    Example:
    RP/0/0/CPU0:router(config)# dhcp ipv4
    
     

    Enters DHCP IPv4 configuration mode.

     
    Step 3 profile profile-name relay


    Example:
    RP/0/0/CPU0:router(config-dhcpv4)# profile client relay
    
     

    Enters DHCP IPv4 profile relay submode.

     
    Step 4 helper-address [vrf vrf- name ] address


    Example:
    RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# helper-address vrf 
    foo 10.10.1.1
    
     

    Forwards UDP broadcasts, including BOOTP and DHCP.

    • The value of the address argument can be a specific DHCP server address or a network address (if other DHCP servers are on the destination network segment). Using the network address enables other servers to respond to DHCP requests.
    • For multiple servers, configure one helper address for each server.
     
    Step 5 Use one of these commands:
    • end
    • commit


    Example:
    RP/0/0/CPU0:router(config)# end

    or

    RP/0/0/CPU0:router(config)# commit
     

    Saves configuration changes.

    • When you issue the end command, the system prompts you to commit changes:
      Uncommitted changes found, commit them
      before exiting(yes/no/cancel)? [cancel]:
      
      • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
      • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
      • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
    • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
     

    Configuring the DHCPv6 (Stateless) Relay Agent

    Perform this task to specify a destination address to which client messages are forwarded and to enable Dynamic Host Configuration Protocol (DHCP) for IPv6 relay service on the interface.

    SUMMARY STEPS

      1.    configure

      2.    dhcp ipv6

      3.    interface type interface-path-id relay

      4.    destination ipv6-address

      5.    Use one of these commands:

      • end
      • commit


    DETAILED STEPS
        Command or Action Purpose
      Step 1 configure


      Example:
      RP/0/0/CPU0:router# configure
       

      Enters global configuration mode.

       
      Step 2 dhcp ipv6


      Example:
      
      RP/0/0/CPU0:router(config) # dhcp ipv6
      RP/0/0/CPU0:router(config-dhcpv6)# 
      
      
       

      Enables DHCP for IPv6 and enters the DHCP IPv6 configuration mode.

       
      Step 3 interface type interface-path-id relay


      Example:
      
      RP/0/0/CPU0:router(config-dhcpv6) # interface tenGigE 0/5/0/0 relay 
      
      
       

      Specifies an interface type and interface-path-id, places the router in interface configuration mode, and enables DHCPv6 relay service on the interface.

       
      Step 4 destination ipv6-address


      Example:
      
      RP/0/0/CPU0:router(config-dhcpv6-if) # destination 10:10::10
      
      
       

      Specifies a destination address to which client packets are forwarded.

      When relay service is enabled on an interface, a DHCP for IPv6 message received on that interface is forwarded to all configured relay destinations. The incoming DHCP for IPv6 message may have come from a client on that interface, or it may have been relayed by another relay agent.

       
      Step 5 Use one of these commands:
      • end
      • commit


      Example:
      RP/0/0/CPU0:router(config)# end

      or

      RP/0/0/CPU0:router(config)# commit
       

      Saves configuration changes.

      • When you issue the end command, the system prompts you to commit changes:
        Uncommitted changes found, commit them
        before exiting(yes/no/cancel)? [cancel]:
        
        • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
        • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
        • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
      • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
       

      Enabling DHCP Relay Agent on an Interface

      This task describes how to enable the Cisco IOS XR DHCP relay agent on an interface.


      Note


      On Cisco IOS XR software, the DHCP relay agent is disabled by default.


      SUMMARY STEPS

        1.    configure

        2.    dhcp ipv4

        3.    interface type name relay profile profile-name

        4.    Use one of these commands:

        • end
        • commit


      DETAILED STEPS
          Command or Action Purpose
        Step 1 configure


        Example:
        RP/0/0/CPU0:router# configure
         

        Enters global configuration mode.

         
        Step 2 dhcp ipv4


        Example:
        RP/0/0/CPU0:router(config-if)# dhcp ipv4 
        
         

        Enters DHCP IPv4 configuration submode.

         
        Step 3 interface type name relay profile profile-name


        Example:
        RP/0/0/CPU0:router(config-dhcpv4)# interface 
        FastEthernet0/0 relay profile client
        
         

        Attaches a relay profile to an interface.

         
        Step 4 Use one of these commands:
        • end
        • commit


        Example:
        RP/0/0/CPU0:router(config)# end

        or

        RP/0/0/CPU0:router(config)# commit
         

        Saves configuration changes.

        • When you issue the end command, the system prompts you to commit changes:
          Uncommitted changes found, commit them
          before exiting(yes/no/cancel)? [cancel]:
          
          • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
          • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
          • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
        • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
         

        Disabling DHCP Relay on an Interface

        This task describes how to disable the DHCP relay on an interface by assigning the none profile to the interface.

        SUMMARY STEPS

          1.    configure

          2.    dhcp ipv4

          3.    interface type name none

          4.    Use one of these commands:

          • end
          • commit


        DETAILED STEPS
            Command or Action Purpose
          Step 1 configure


          Example:
          RP/0/0/CPU0:router# configure
           

          Enters global configuration mode.

           
          Step 2 dhcp ipv4


          Example:
          RP/0/0/CPU0:router(config)# dhcp ipv4
          
           

          Enters DHCP IPv4 configuration submode.

           
          Step 3 interface type name none


          Example:
          RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# interface 
          pos 0/1/4/1 none
          
           

          Disables the DHCP relay on the interface.

           
          Step 4 Use one of these commands:
          • end
          • commit


          Example:
          RP/0/0/CPU0:router(config)# end

          or

          RP/0/0/CPU0:router(config)# commit
           

          Saves configuration changes.

          • When you issue the end command, the system prompts you to commit changes:
            Uncommitted changes found, commit them
            before exiting(yes/no/cancel)? [cancel]:
            
            • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
            • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
            • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
          • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
           

          Enabling DHCP Relay on a VRF

          This task describes how to enable DHCP relay on a VRF.

          SUMMARY STEPS

            1.    configure

            2.    dhcp ipv4

            3.    vrf vrf-name relay profile profile-name

            4.    Use one of these commands:

            • end
            • commit


          DETAILED STEPS
              Command or Action Purpose
            Step 1 configure


            Example:
            RP/0/0/CPU0:router# configure
             

            Enters global configuration mode.

             
            Step 2 dhcp ipv4


            Example:
            RP/0/0/CPU0:router(config)# dhcp ipv4
            
             

            Enters DHCP IPv4 configuration submode.

             
            Step 3 vrf vrf-name relay profile profile-name


            Example:
            RP/0/0/CPU0:router(config-dhcpv4)
            #vrf default relay profile client
            
             

            Enables DHCP relay on a VRF.

             
            Step 4 Use one of these commands:
            • end
            • commit


            Example:
            RP/0/0/CPU0:router(config)# end

            or

            RP/0/0/CPU0:router(config)# commit
             

            Saves configuration changes.

            • When you issue the end command, the system prompts you to commit changes:
              Uncommitted changes found, commit them
              before exiting(yes/no/cancel)? [cancel]:
              
              • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
              • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
              • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
            • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
             

            Configuring the Relay Agent Information Feature

            This task describes how to configure the DHCP relay agent information option processing capabilities.

            A DHCP relay agent may receive a message from another DHCP relay agent that already contains relay information. By default, the relay information from the previous relay agent is replaced (using the replace option).

            SUMMARY STEPS

              1.    configure

              2.    dhcp ipv4

              3.    profile profile-name relay

              4.    relay information option

              5.    relay information check

              6.    relay information policy {drop | keep}

              7.    relay information option allow-untrusted

              8.    Use one of these commands:

              • end
              • commit


            DETAILED STEPS
                Command or Action Purpose
              Step 1 configure


              Example:
              RP/0/0/CPU0:router# configure
               

              Enters global configuration mode.

               
              Step 2 dhcp ipv4


              Example:
              RP/0/0/CPU0:router(config)# dhcp ipv4
              
               

              Enters DHCP IPv4 configuration mode.

               
              Step 3 profile profile-name relay


              Example:
              RP/0/0/CPU0:router(config-dhcpv4)# profile client relay
              
               

              Enters DHCP IPv4 profile relay mode.

               
              Step 4 relay information option


              Example:
              RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# relay information option
              
               

              Enables the system to insert the DHCP relay agent information option (option-82 field) in forwarded BOOTREQUEST messages to a DHCP server.

              • This option is injected by the relay agent while forwarding client-originated DHCP packets to the server. Servers recognizing this option can use the information to implement IP address or other parameter assignment policies. When replying, the DHCP server echoes the option back to the relay agent. The relay agent removes the option before forwarding the reply to the client.
              • The relay agent information is organized as a single DHCP option that contains one or more suboptions. These options contain the information known by the relay agent. The supported suboptions are:
                • Remote ID
                • Circuit ID
              Note   

              This function is disabled by default.

               
              Step 5 relay information check


              Example:
              RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# relay information check
              
               

              (Optional) Configures DHCP to check that the relay agent information option in forwarded BOOTREPLY messages is valid.

              • By default, DHCP checks that the option-82 field in DHCP reply packets, received from the DHCP server, is valid. If an invalid message is received, the relay agent drops the message. If a valid message is received, the relay agent removes the option-82 field and forwards the packet.
              Note   

              Use the relay information check command to reenable this functionality if the functionality has been disabled.

               
              Step 6 relay information policy {drop | keep}


              Example:
              RP/0/0/CPU0:router(config)# dhcp relay information policy drop
              
               

              (Optional) Configures the reforwarding policy for a DHCP relay agent; that is, whether the relay agent will drop or keep the relay information.

               
              Step 7 relay information option allow-untrusted


              Example:
              RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# relay information check
              
               

              (Optional) Configures the DHCP IPv4 Relay not to discard BOOTPREQUEST packets that have an existing relay information option and the giaddr set to zero.

               
              Step 8 Use one of these commands:
              • end
              • commit


              Example:
              RP/0/0/CPU0:router(config)# end

              or

              RP/0/0/CPU0:router(config)# commit
               

              Saves configuration changes.

              • When you issue the end command, the system prompts you to commit changes:
                Uncommitted changes found, commit them
                before exiting(yes/no/cancel)? [cancel]:
                
                • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
                • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
                • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
              • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
               

              Configuring Relay Agent Giaddr Policy

              This task describes how to configure BOOTPREQUEST packets for Dynamic Host Configuration Protocol (DHCP) IPv4 Relay processes, that already contain a nonzero giaddr attribute.

              SUMMARY STEPS

                1.    configure

                2.    dhcp ipv4

                3.    profile profile-name relay

                4.    giaddr policy {replace | drop}

                5.    Use one of these commands:

                • end
                • commit


              DETAILED STEPS
                  Command or Action Purpose
                Step 1 configure


                Example:
                RP/0/0/CPU0:router# configure
                 

                Enters global configuration mode.

                 
                Step 2 dhcp ipv4


                Example:
                RP/0/0/CPU0:router(config)# dhcp ipv4
                
                 

                Enables the DHCP IPv4 configuration submode.

                 
                Step 3 profile profile-name relay


                Example:
                RP/0/0/CPU0:router(config-dhcpv4)# profile client relay
                
                 

                Enables profile relay submode.

                 
                Step 4 giaddr policy {replace | drop}


                Example:
                RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# giaddr policy drop
                
                 

                Specifies the giaddr policy.

                • replaceReplaces the existing giaddr value with a value that it generates.
                • dropDrops the packet that has an existing nonzero giaddr value.
                 
                Step 5 Use one of these commands:
                • end
                • commit


                Example:
                RP/0/0/CPU0:router(config)# end

                or

                RP/0/0/CPU0:router(config)# commit
                 

                Saves configuration changes.

                • When you issue the end command, the system prompts you to commit changes:
                  Uncommitted changes found, commit them
                  before exiting(yes/no/cancel)? [cancel]:
                  
                  • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
                  • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
                  • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
                • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
                 

                Configuring the Broadcast Flag Policy

                This task describes how to configure DHCP IPv4 Relay to broadcast BOOTPREPLY packets only if the DHCP IPv4 broadcast flag is set in the DHCP IPv4 header.


                Note


                By default, the DHCP IPv4 Relay always broadcasts BOOTPREPLY packets.


                SUMMARY STEPS

                  1.    configure

                  2.    dhcp ipv4

                  3.    profile profile-name relay

                  4.    broadcast-flag policy check

                  5.    Use one of these commands:

                  • end
                  • commit


                DETAILED STEPS
                    Command or Action Purpose
                  Step 1 configure


                  Example:
                  RP/0/0/CPU0:router# configure
                   

                  Enters global configuration mode.

                   
                  Step 2 dhcp ipv4


                  Example:
                  RP/0/0/CPU0:router(config)# dhcp ipv4
                  
                   

                  Configures DHCP IPv4 mode.

                   
                  Step 3 profile profile-name relay


                  Example:
                  RP/0/0/CPU0:router(config-dhcpv4)# profile client relay
                  
                   

                  Enables profile relay mode.

                   
                  Step 4 broadcast-flag policy check


                  Example:
                  RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# broadcast-flag policy check
                  
                   

                  Enables checking of the broadcast flag in packets.

                   
                  Step 5 Use one of these commands:
                  • end
                  • commit


                  Example:
                  RP/0/0/CPU0:router(config)# end

                  or

                  RP/0/0/CPU0:router(config)# commit
                   

                  Saves configuration changes.

                  • When you issue the end command, the system prompts you to commit changes:
                    Uncommitted changes found, commit them
                    before exiting(yes/no/cancel)? [cancel]:
                    
                    • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
                    • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
                    • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
                  • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
                   

                  Information About Configuring DHCP IPv6 Information Pools

                  A DHCP IPv6 configuration information pool is a named entity that includes information about available configuration parameters and policies that control assignment of the parameters to clients from the pool. A pool is configured independently of the DHCP service and is associated with the DHCP service through the command line interface.

                  Each configuration pool can contain the following configuration parameters and operational information:

                  • Prefix delegation information, which could include a list of available prefixes for a particular client and associated preferred and valid lifetimes
                  • Domain name service (DNS) servers—List of IPv6 addresses of DNS servers
                  • Domain search list—String containing domain names for DNS resolution
                  • SIP server address—List of IPv6 addresses of SIP server
                  • SIP server domain list—String containing domain names for SIP server

                  How to Configure DHCP IPv6 Information Pools

                  This section contains the following task:

                  Configuring Cisco IOS XR DHCP IPv6 Information Pool Option

                  This task describes how to enable support for the DHCP IPv6 information pool option with the name pool1.

                  SUMMARY STEPS

                    1.    configure

                    2.    dhcp ipv6

                    3.    pool pool-name

                    4.    Use one of these commands:

                    • end
                    • commit

                    5.    show dhcp ipv6 pool [ pool-name ]


                  DETAILED STEPS
                      Command or Action Purpose
                    Step 1 configure


                    Example:
                    RP/0/0/CPU0:router# configure
                     

                    Enters global configuration mode.

                     
                    Step 2 dhcp ipv6


                    Example:
                    RP/0/0/CPU0:router (config)# dhcp ipv6
                    
                     

                    Enables the DHCP IPv6 configuration mode.

                     
                    Step 3 pool pool-name


                    Example:
                    RP/0/0/CPU0:router (config-dhcp ipv6)# pool pool1
                    
                     

                    Creates a DHCP pool specified by the pool-name argument for the prefix delegation and the other configurations on the interface.

                     
                    Step 4 Use one of these commands:
                    • end
                    • commit


                    Example:
                    RP/0/0/CPU0:router(config)# end

                    or

                    RP/0/0/CPU0:router(config)# commit
                     

                    Saves configuration changes.

                    • When you issue the end command, the system prompts you to commit changes:
                      Uncommitted changes found, commit them
                      before exiting(yes/no/cancel)? [cancel]:
                      
                      • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
                      • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
                      • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
                    • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
                     
                    Step 5 show dhcp ipv6 pool [ pool-name ]


                    Example:
                    RP/0/0/CPU0:router# show dhcp ipv6 pool pool1
                    
                     

                    (Optional) Displays the DHCP IPv6 pool name.

                     

                    Configuration Examples for the DHCP Relay Agent

                    This section provides the following configuration examples:

                    DHCP Relay Profile: Example

                    The following example shows how to configure the Cisco IOS XR relay profile:

                    dhcp ipv4 
                     profile client relay
                      helper-address vrf foo 10.10.1.1
                     !        
                    ! ...
                    
                    

                    DHCP Relay on an Interface: Example

                    The following example shows how to enable the DHCP relay agent on an interface:

                    dhcp ipv4
                     interface gigabitethernet 0/1/1/0 relay profile client
                    !
                    
                    

                    DHCP Relay on a VRF: Example

                    The following example shows how to enable the DHCP relay agent on a VRF:

                    dhcp ipv4
                     vrf default relay profile client
                    !
                    
                    

                    Relay Agent Information Option Support: Example

                    The following example shows how to enable the relay agent and the insertion and removal of the DHCP relay information option:

                    dhcp ipv4
                     profile client relay
                    relay information 
                    check
                     !
                    !
                    
                    

                    Relay Agent Giaddr Policy: Example

                    The following example shows how to configure relay agent giaddr policy:

                    dhcp ipv4
                     profile client relay
                      giaddr policy drop
                     !
                    !
                    
                    

                    Cisco IOS XR Broadcast Flag Policy: Example

                    This task describes how to configure DHCP IPv4 Relay to broadcast BOOTPREPLY packets only if the DHCP IPv4 broadcast flag is set in the DHCP IPv4 header.


                    Note


                    By default, the DHCP IPv4 Relay always broadcasts BOOTPREPLY packets.


                    SUMMARY STEPS

                      1.    configure

                      2.    dhcp ipv4

                      3.    profile profile name relay

                      4.    broadcast-flag policy check

                      5.    Use one of these commands:

                      • end
                      • commit


                    DETAILED STEPS
                        Command or Action Purpose
                      Step 1 configure


                      Example:
                      RP/0/0/CPU0:router# configure
                       

                      Enters global configuration mode.

                       
                      Step 2 dhcp ipv4


                      Example:
                      RP/0/0/CPU0:router(config)# dhcp ipv4
                      
                       

                      Configures DHCP IPv4 mode.

                       
                      Step 3 profile profile name relay


                      Example:
                      RP/0/0/CPU0:router(config-dhcpv4)# profile client relay
                      
                       

                      Enables profile relay mode.

                       
                      Step 4 broadcast-flag policy check


                      Example:
                      RP/0/0/CPU0:router(config-dhcpv4-relay-profile)# broadcast-flag policy check
                      
                       

                      Enables checking of the broadcast flag in packets.

                       
                      Step 5 Use one of these commands:
                      • end
                      • commit


                      Example:
                      RP/0/0/CPU0:router(config)# end

                      or

                      RP/0/0/CPU0:router(config)# commit
                       

                      Saves configuration changes.

                      • When you issue the end command, the system prompts you to commit changes:
                        Uncommitted changes found, commit them
                        before exiting(yes/no/cancel)? [cancel]:
                        
                        • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
                        • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
                        • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
                      • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
                       

                      Additional References

                      The following sections provide references related to implementing the Cisco IOS XR DHCP relay agent.

                      Related Documents

                      Related Topic

                      Document Title

                      Cisco IOS XR

                      DHCP commands

                      DHCP Commands module in the Cisco IOS XR IP Addresses and Services Command Reference for the Cisco XR 12000 Series Router

                      Getting started material

                      Cisco IOS XR Getting Started Guide for the Cisco XR 12000 Series Router

                      Information about user groups and task IDs

                      Configuring AAA Services module in the Cisco IOS XR System Security Configuration Guide for the Cisco XR 12000 Series Router

                      Standards

                      Standards

                      Title

                      No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

                      MIBs

                      MIBs

                      MIBs Link

                      To locate and download MIBs, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http:/​/​cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

                      RFCs

                      RFC

                      Title

                      RFC 2131

                      RFC 3315

                      Dynamic Host Configuration Protocol

                      Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

                      Technical Assistance

                      Description

                      Link

                      The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

                      http:/​/​www.cisco.com/​techsupport