Configuration Guide for Cisco NCS 1004, IOS XR Release 25.x.x

PDF

Configuration Guide for Cisco NCS 1004, IOS XR Release 25.x.x

DHCP client

Updated: July 31, 2026

Want to summarize with AI?

Log in

This section explains how DHCP clients allow router interfaces to automatically acquire IP addresses and configuration information.

The DHCP client is a feature that enables router interfaces on the NCS 1004 to dynamically acquire an IPv4 or DHCPv6 server address, and forwards responses back to the correct Layer 2 address so that the correct device gets the correct configuration information.

A DHCP client is a network feature that

  • dynamically acquires an IPv4 or DHCPv6 server address for router interfaces,

  • allocates IP addresses to devices for a configurable lease period, and

  • automatically renews leases and forwards responses to the correct Layer 2 address to ensure proper device configuration.

Feature history

Table 1. Feature history

Feature name

Release information

Feature description

Dynamic Host Configuration Protocol (DHCP) Client

Cisco IOS XR Release 7.3.2

The DHCP client enables the router interfaces to dynamically acquire the IPv4 or DHCPv4 or DHCPv6 server which is used to forward the response to the correct layer 2 address. The DHCP client ensures that configuration information reaches the correct device.

The Dynamic Host Configuration Protocol (DHCP) client functionality enables the router interfaces to dynamically acquire the IPv4 or DHCPv4 or DHCPv6 server, and forwards the responses back to the correct Layer 2 address so that the correct device gets the correct configuration information.

DHCP has the ability to allocate IP addresses only for a configurable period of time, called the lease period. If the client is required to retain this IP address for a longer period beyond the lease period, the lease period must be renewed before the IP address expires. The client renews the lease based on configuration that was sent from the server. The client unicasts a REQUEST message using the IP address of the server. When a server receives the REQUEST message and responds with an ACK message. The lease period of the client is extended by the lease time configured in the ACK message. DHCP client supports DHCPv6.

DHCP client options

A DHCP client option is a configuration parameter for DHCPv6 clients that

  • enables device identification and network communication,

  • allows customization of DHCP client behavior, and

  • supports interoperability with various DHCP servers and network requirements.

Available DHCPv6 client options

The available DHCPv6 client options are:

  • DUID: When configured, the DHCPv6 client communicates with the DHCPv6 server through the link layer address.

  • Rapid commit: When configured, the DHCPv6 client obtains configuration parameters from the DHCPv6 server through a rapid two-step exchange (solicit and reply) instead of the default four-step exchange (solicit, advertise, request, and reply).

  • DHCP options:

    • Option 15: User Class option. Used by a DHCPv6 client to identify the type or category of users or applications it represents.

    • Option 16: Vendor ID option. Used by a DHCPv6 client to identify the vendor that manufactured the hardware on which the client is running.

    • Option 23: Domain Name Server (DNS) option. Provides a list of IPv6 addresses of DNS recursive name servers to which the client's DNS resolver can send DNS queries.

    • Option 24: Domain List option. Specifies the domain search list that the client uses to resolve hostnames with the DNS.

  • DHCP timers: Used to set different timer values for DHCP client configurations. The various DHCP timer options are:

    • Release-timeout: Retransmission timeout value for the initial release message.

    • Req-max-rt: Maximum retransmission timeout value for the request message.

    • Sol-max-delay: Maximum delay time of the first solicit message.

    • Sol-max-rt: Maximum solicit retransmission time.

    • Sol-time-out: Initial timeout value of the solicit message.

Enable DHCP client on management Ethernet interface

Enable the DHCP client to facilitate automatic IPv6 address configuration on the management Ethernet interface.
Follow these steps to enable and verify the DHCP client on the management Ethernet interface:

Procedure

1.

Run the configure interface MgmtEth R/S/I/P ipv6 address dhcp-client-options duid linked-layer-addressrapid-commit{option 16 vendor | option 15 ciscoupnnp | option 23 | option 24 timers sol-max-delay value | timers sol-time-out value | timers req-timeout value | timers req-max-rt value | timers release-timeout value} ipv6 address dhcp to enable DHCP client on the management Ethernet interface.

Example:

This is a sample to enable DHCP client on the management Ethernet interface:


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#interface MgmtEth0/0/CPU0/0
RP/0/RP0/CPU0:ios(config)#ipv6 address dhcp-client-options
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#duid linked-layer-address
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#rapid-commit
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#option 16 vendor
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#option 15 ciscoupnnp
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#option 23
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#option 24
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers sol-max-delay 1
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers sol-time-out 1
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers sol-max-rt 120
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers req-timeout 1
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers req-max-rt 30
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#timers release-timeout 1
RP/0/RP0/CPU0:ios(config-dhcpv6-client)#commit
2.

Run the show dhcp ipv6 client and show dhcp ipv6 client detail command to verify DHCP client options on the management Ethernet interface.

Example:


RP/0/0/CPU0:ios#show dhcp ipv6 client
Thu Sep 17 10:45:44.493 IST

Interface name IPv6 Address State Lease Time Rem
---------------------- -------------- --------------- --------------------
MgmtEth0/0/1/0 500:1::1a/128 BOUND 7116


RP/0/RP0/CPU0:ios#show dhcp ipv6 client detail
Thu Sep 17 10:45:48.880 IST

-----------------------------------------------------
Client Interface name : MgmtEth0/0/`/0
Client Interface handle : 0x4040
Client MACAddr : 0219.bc81.e750
Client State : BOUND
Client Link Local Address : fe80::19:bcff:fe81:e750
Client IPv6 Address (Dhcp) : 500:1::1a/128
Lease Remaining (in secs) : 7112
DUID : 000300010219bc81e750

Client Configuration
Timers
SOL_MAX_DELAY : 1 secs (00:00:01)
SOL_TIMEOUT : 1 secs (00:00:01)
SOL_MAX_RT : 120 secs (00:02:00)
REQ_TIMEOUT : 1 secs (00:00:01)
REQ_MAX_RT : 30 secs (00:00:30)
REL_TIMEOUT : 1 secs (00:00:01)

Options
RAPID-COMMIT : True
USER-CLASS : ciscoupnnp
VENDOR-CLASS : vendor
DNS-SERVERS : True
DOMAIN-LIST : True

DUID Type : DUID_LL

Server Information
Server Address : fe80::1a:19ff:fe03:99ca
Preference : 255
DUID : 000300010206826e2e00
Status : SUCCESS
IA-NA
Status : SUCCESS
IAID : 0x40400001
T1 : 3600 secs (01:00:00)
T2 : 5760 secs (01:36:00)
IA-ADDR
IA NA Address : 500:1::1a
Preferred Time : 7200 secs (02:00:00)
Valid Time : 7200 secs (02:00:00)
Flags : 0x0
-----------------------------------------------------

The DHCP client is enabled on the management Ethernet interface. The interface automatically receives IPv6 address assignments and DHCP options from the DHCP server.