What three-digit DHCP option defines the DNS domain name that will be configured on DHCP clients

(Optional) Configuring a DHCP Server to Allocate Network Parameters Besides IP Addresses

Context

DHCP servers can allocate other network parameters as well as IP addresses to DHCP clients. These parameters include the IP address of a DNS server, startup configuration file, and self-defined options.

Inhaltsverzeichnis Show

(Optional) Configuring a DHCP Server to Allocate Network Parameters Besides IP Addresses
What is the DHCP option for DNS?
Which DHCP client option is used to provide a list of IP addresses for DNS servers?
How does a DHCP server respond to an IP request that can't be renewed?
What RFC defines the DNS resource record types?

When network parameters, excluding the IP address, are allocated to dynamic and static clients, configuration commands are the same if an interface address pool is used, but are different if a global address pool is used. This is because of the following:

Network parameters for dynamic clients are configured in the global address pool view.
Network parameters for static clients are configured in the global address pool and DHCP Option template views. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.

Configuring a Gateway Address for Clients
Configuring DNS and the NetBIOS Service on the DHCP Clients
Configuring a Configuration File for a DHCP Client
Configuring User-defined Options for Clients

Configuring a Gateway Address for Clients

Context

When a DHCP client connects to a DHCP server or host outside the local network segment, data must be forwarded through an egress gateway. You can configure the gateway address for clients. This configuration is required only when the global address pool is used. When the interface address pool is used, the gateway address is the IP address of the interface connecting the DHCP server to the DHCP client.

NOTE:

For a global address pool, if a gateway address is configured on the DHCP server, a DHCP client obtains the gateway address from the DHCP server and automatically generates a default route to the gateway address. If you run the option121 command on the DHCP server to allocate classless static routes to DHCP clients, the DHCP client uses an allocated classless static route and does not automatically generate a default route to the gateway address.
For an interface address pool, the egress gateway address is the IP address of the interface connecting the DHCP server to the DHCP client. The DHCP client obtains the IP address as the gateway address and automatically generates a default route to the gateway address. If you run the dhcp server option121 command on the DHCP server to allocate classless static routes to DHCP clients, the DHCP client uses an allocated classless static route and does not automatically generate a default route to the gateway address.

Do not configure a gateway address for DHCP clients in the following scenarios:

When no DHCP relay agent is deployed, the gateway address is the IP address of the interface connecting the DHCP server to the DHCP client.
When a DHCP relay agent is deployed, the gateway address is the IP address of the interface connecting the DHCP relay agent to the client.

In a scenario where Virtual Router Redundancy Protocol (VRRP) and DHCP are deployed, if the VRRP group functions as the DHCP server, perform this task to configure the group virtual IP address as the gateway address.

To load balance traffic and improve network reliability, configure multiple egress gateways. Each address pool can be configured with a maximum of eight gateway addresses.

When a global address pool is used to allocate network parameters, configuration commands are different for dynamic and static clients. Network parameters for dynamic clients are configured in the global address pool view, whereas network parameters for static clients are configured in the global address pool view or DHCP Option template view. The DHCP Option template must be configured when static clients require network parameters that are different from those of dynamic clients. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.

Procedure

In the global address pool view:
1. Run:
```
system-view
```
  The system view is displayed.
2. Run:
```
ip pool ip-pool-name
```
  The global address pool view is displayed.
3. Run:
```
gateway-list ip-address &<1-8>
```
  A gateway address for DHCP clients is configured.
  By default, no egress gateway address is configured.
In the DHCP Option template view:
1. Run:
```
system-view
```
  The system view is displayed.
2. Run:
```
dhcp option template template-name
```
  A DHCP Option template is created and its view is displayed.
  By default, no DHCP Option template is created on a device.
  To allocate network parameters (except IP addresses) to static clients, configure a DHCP Option template. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.
  To allocate IP addresses only to static clients (for details, see (Optional) Configuring a DHCP Server to Allocate Fixed IP Addresses to Specified Clients), you do not need to configure a DHCP Option template.
3. Run:
```
gateway-list ip-address &<1-8>
```
  A gateway address for DHCP clients is configured.
  By default, no egress gateway address is configured.
  If you need to configure other items in the DHCP Option template view, complete them first before performing the following steps.
4. (Optional) Run:
```
quit
```
  Return to the system view.
5. (Optional) Run:
```
ip pool ip-pool-name
```
  The global address pool view is displayed.
6. (Optional) Run:
```
static-bind ip-address ip-address mac-address mac-address option-template template-name
```
  A DHCP Option template is bound to static clients.

Configuring DNS and the NetBIOS Service on the DHCP Clients

Context

To enable DHCP clients to communicate with devices on other networks through host names, configure the DNS or NetBIOS service.

DNS, defined by RFC 1034 and provided by TCP/IP, translates host names into IP addresses.

NetBIOS, defined by IBM, is applicable to small LANs with dozens of PCs to provide the following services:

Host naming service on a network segment through UDP port 137
Data services (through UDP port 138), including transmitting data between programs, notifying browser services, and setting up network neighbors on users' desktop systems
Session services (through TCP port 139), including file sharing and printing

Clients running on the Microsoft Windows operating system use the NetBIOS protocol for communication. When such clients are used, the Windows Internet Naming Service (WINS) server translates host names into IP addresses. NetBIOS is vulnerable to attacks, so it is optional on Windows operating systems later than Windows 2000. Users can enable or disable NetBIOS as required.

When a DHCP client uses the NetBIOS protocol for communication, its host name must be mapped to an IP address. Based on the modes to obtain mapping, NetBIOS nodes are classified into the following types:

b-node: indicates a node in broadcast mode. This node obtains its mapping in broadcast mode.
p-node: indicates a node in peer-to-peer mode. This node obtains its mapping by communicating with the NetBIOS server in unicast mode.
m-node: indicates a node in mixed mode. An m-node is a p-node that has certain broadcast features. The node first sends broadcast packets to obtain its mapping. If no mapping is obtained, the node sends unicast packets.
h-node: indicates a node in hybrid mode. An h-node is a b-node enabled with an end-to-end communication mechanism. The node first sends unicast packets to obtain its mapping. If no mapping is obtained, the node sends broadcast packets.

When installing a Microsoft Windows operating system on a PC, you must define a host name. Otherwise, the system generates a host name at random. Host names are unique on a network.

The DNS server IP address, DNS domain name suffix, and NetBIOS server IP address in the address pool can be statistically specified or automatically obtained. The NetBIOS node type can only be statically specified.

If the configuration is to be automatically obtained, the device as the DHCP server also needs to function as the DHCP client (the DHCP client function is configured on the interface connected to the remote DHCP server). The device obtains the DNS server IP address, DNS domain name suffix, and NetBIOS server IP address from the remote DHCP server, and then uses the import function of the address pool to allocate the information to the downlink client. For example, the DHCP server of a company needs to obtain the uniform DNS server IP address, DNS domain name suffix, and NetBIOS server IP address from the carrier, and allocate the information to the downlink client. In this case, the configuration can be automatically obtained.
If the configuration needs to be specified after the automatically obtaining function is enabled, the statically specifying method is used.

NOTE:

If the address pool contains the configurations that are statistically specified and automatically obtained, the statistically specified configuration takes precedence.

Procedure

Based on an interface address pool:
- Configure a DNS service.
  1. Run:
```
system-view
```
    The system view is displayed.
  2. Run:
```
interface interface-type interface-number [.subinterface-number ]
```
    The interface view or sub-interface view is displayed.
  3. Configure the address pool to allocate the automatically obtained DNS configuration to the DHCP clients.
    
    Run:
```
dhcp server import all
```
    The address pool is configured to allocate the automatically obtained DNS configuration to the DHCP clients.
    By default, the address pool does not allocate the automatically obtained DNS configuration to the DHCP clients.
    Configure the address pool to allocate the statically specified DNS configuration to the DHCP clients.
    - Run:
```
dhcp server dns-list ip-address &<1-8>
```
      The DNS server IP address is specified for the DHCP clients.
      By default, no DNS server IP address is configured.
      Each address pool can be configured with a maximum of eight DNS server IP addresses.
    - Run:
```
dhcp server domain-name domain-name
```
      The DNS domain name suffix allocated to the DHCP clients is configured.
      By default, no DNS domain name suffix is configured.
- Configure a NetBIOS service.
  1. Run:
```
system-view
```
    The system view is displayed.
  2. Run:
```
interface interface-type interface-number [.subinterface-number ]
```
    The interface view or sub-interface view is displayed.
  3. Configure the address pool to allocate the automatically obtained NetBIOS server IP address to the DHCP client.
    Run:
```
dhcp server import all
```
    The address pool is configured to allocate the automatically obtained NetBIOS server IP address to the DHCP clients.
    By default, the address pool does not allocate the automatically obtained NetBIOS server IP address to the DHCP clients.
    Configure the address pool to allocate the statically specified NetBIOS configuration to the DHCP clients.
    - Run:
```
dhcp server nbns-list ip-address &<1-8>
```
      The NetBIOS server IP address is specified for the DHCP clients.
      By default, no NetBIOS server IP address is configured.
      Each address pool can be configured with a maximum of eight NetBIOS server IP addresses.
    - Run:
```
dhcp server netbios-type { b-node | h-node | m-node | p-node }
```
      The NetBIOS node type is specified.
      By default, no NetBIOS node type is specified.
Based on a global address pool:
- In the global address pool view:
  - Configure a DNS service.
    1. Run:
```
system-view
```
      The system view is displayed.
    2. Run:
```
ip pool ip-pool-name
```
      The global address pool view is displayed.
    3. Configure the address pool to allocate the automatically obtained DNS configuration to the DHCP clients.
      The address pool is configured to allocate the automatically obtained DNS configuration to the DHCP clients.
      By default, the address pool does not allocate the automatically obtained DNS configuration to the DHCP clients.
      Configure the address pool to allocate the statically specified DNS configuration to the DHCP clients.
      - Run:
        dns-list ip-address &<1-8>
        The DNS server IP address is specified for the DHCP clients.
        By default, no DNS server IP address is configured.
        Each address pool can be configured with a maximum of eight DNS server IP addresses.
      - Run:
        domain-name domain-name
        The domain name suffix to be assigned to the DHCP clients is configured.
        By default, no DNS domain name suffix is configured.
  - Configure a NetBIOS service.
    1. Run:
```
system-view
```
      The system view is displayed.
    2. Run:
```
ip pool ip-pool-name
```
      The global address pool view is displayed.
    3. Configure the address pool to allocate the automatically obtained NetBIOS server IP address to the DHCP client.
      The address pool is configured to allocate the automatically obtained NetBIOS server IP address to the DHCP clients.
      By default, the address pool does not allocate the automatically obtained NetBIOS server IP address to the DHCP clients.
      
      Configure the address pool to allocate the statically specified NetBIOS configuration to the DHCP clients.
      - Run:
        nbns-list ip-address &<1-8>
        The NetBIOS server address that a DHCP server delivers to a DHCP client is specified.
        By default, no NetBIOS server IP address is configured.
        Each address pool can be configured with a maximum of eight NetBIOS server IP addresses.
      - Run:
        netbios-type { b-node | h-node | m-node | p-node }
        The NetBIOS node type is specified.
        By default, no NetBIOS node type is specified.
- In the DHCP Option template view:
  - Configure a DNS service.
    1. Run:
```
system-view
```
      The system view is displayed.
    2. Run:
```
dhcp option template template-name
```
      A DHCP Option template is created and its view is displayed.
      By default, no DHCP Option template is created on a device.
      To allocate network parameters (except IP addresses) to static clients, configure a DHCP Option template. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.
      To allocate IP addresses only to static clients (for details, see (Optional) Configuring a DHCP Server to Allocate Fixed IP Addresses to Specified Clients), you do not need to configure a DHCP Option template.
    3. Run the following commands to configure the IP address of the DNS server and domain name for the DHCP clients.
      - Run:
        
        dns-list ip-address &<1-8>
        The IP address of the DNS server is configured for DHCP clients.
        By default, no DNS server IP address is configured in an address pool.
        Each address pool can be configured with a maximum of eight DNS server IP addresses.
      - Run:
        domain-name domain-name
        The domain name is allocated to DHCP clients.
        By default, no domain name is allocated.
      If you need to configure other items in the DHCP Option template view, complete them first before performing the following steps.
    4. (Optional) Run:
```
quit
```
      Return to the system view.
    5. (Optional) Run:
```
ip pool ip-pool-name
```
      The global address pool view is displayed.
    6. (Optional) Run:
```
static-bind ip-address ip-address mac-address mac-address option-template template-name
```
      A DHCP Option template is bound to static clients.
  - Configure a NetBIOS service.
    1. Run:
```
system-view
```
      The system view is displayed.
    2. Run:
```
dhcp option template template-name
```
      A DHCP Option template is created and its view is displayed.
      By default, no DHCP Option template is created on a device.
      To allocate network parameters (except IP addresses) to static clients, configure a DHCP Option template. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.
      To allocate IP addresses only to static clients (for details, see (Optional) Configuring a DHCP Server to Allocate Fixed IP Addresses to Specified Clients), you do not need to configure a DHCP Option template.
    3. Run the following commands to configure the IP address of the NetBIOS server and NetBIOS node type for the DHCP clients.
      - Run:
        nbns-list ip-address &<1-8>
        The IP address of the NetBIOS server is configured for DHCP clients.
        By default, no NetBIOS server IP address is configured in an address pool.
        Each address pool can be configured with a maximum of eight NetBIOS server IP addresses.
      - Run:
        netbios-type { b-node | h-node | m-node | p-node }
        The NetBIOS node type for DHCP clients is configured.
        By default, no NetBIOS node type is configured for DHCP clients.
      If you need to configure other items in the DHCP Option template view, complete them first before performing the following steps.
    4. (Optional) Run:
```
quit
```
      Return to the system view.
    5. (Optional) Run:
```
ip pool ip-pool-name
```
      The global address pool view is displayed.
    6. (Optional) Run:
```
static-bind ip-address ip-address mac-address mac-address option-template template-name
```
      A DHCP Option template is bound to static clients.

Configuring a Configuration File for a DHCP Client

Context

Some clients require certain network parameters, in addition to IP addresses, to be configured before they can work normally. A DHCP server can allocate configuration information such as the startup configuration file to clients. Configuration files are usually saved on the DHCP server or a dedicated file server. The DHCP server can specify the address of the file server so that clients can easily obtain files from the file server.

If the startup configuration file is saved on a file server, the route between the DHCP client and file server must be reachable.

Procedure

Configure a configuration file based on an interface address pool.
1. Run:
```
system-view
```
  The system view is displayed.
2. Run:
```
interface interface-type interface-number [.subinterface-number ]
```
  The interface view or sub-interface view is displayed.
3. Run:
```
dhcp server bootfile bootfile
```
  The name of the startup configuration file for DHCP clients is configured.
  By default, the name is not configured.
4. Run:
```
dhcp server sname sname
```
  The name of the server from which DHCP clients obtain the startup configuration file is configured.
  By default, the name of the server is not configured.
5. Run:
```
dhcp server next-server ip-address
```
  The IP address of the server is configured for the client after the client automatically obtains an IP address.
  By default, the server IP address is not configured.
  You can also specify an IP address for the file server by configuring user-defined options for clients.
Configure a configuration file based on a global address pool.
- In the global address pool view:
  1. Run:
```
system-view
```
    The system view is displayed.
  2. Run:
```
ip pool ip-pool-name
```
    The global address pool view is displayed.
  3. Run:
```
bootfile bootfile
```
    The name of the startup configuration file for DHCP clients is configured.
    By default, the name is not configured.
  4. Run:
```
sname sname
```
    The name of the server from which DHCP clients obtain the startup configuration file is configured.
    By default, the name of the server is not configured.
  5. Run:
```
next-server ip-address 
```
    The IP address of a network service server is configured for the client after the client automatically obtains an IP address.
    By default, the server IP address is not configured.
    You can also specify an IP address for the file server by configuring user-defined options for clients.
- In the DHCP Option template view:
  1. Run:
```
system-view
```
    The system view is displayed.
  2. Run:
```
dhcp option template template-name
```
    A DHCP Option template is created and its view is displayed.
    By default, no DHCP Option template is created on a device.
    To allocate network parameters (except IP addresses) to static clients, configure a DHCP Option template. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.
    To allocate IP addresses only to static clients (for details, see (Optional) Configuring a DHCP Server to Allocate Fixed IP Addresses to Specified Clients), you do not need to configure a DHCP Option template.
  3. Run:
```
bootfile bootfile
```
    The name of the startup configuration file for DHCP clients is configured.
    By default, the name is not configured.
  4. Run:
```
sname sname
```
    The name of the server from which DHCP clients obtain the startup configuration file is configured.
    By default, the name of the server is not configured.
  5. Run:
```
next-server ip-address
```
    The IP address of a network service server is configured for the client after the client automatically obtains an IP address.
    By default, the server IP address is not configured.
    You can also specify an IP address for the file server by configuring user-defined options for clients.
    If you need to configure other items in the DHCP Option template view, complete them first before performing the following steps.
  6. (Optional) Run:
```
quit
```
    Return to the system view.
  7. (Optional) Run:
```
ip pool ip-pool-name
```
    The global address pool view is displayed.
  8. (Optional) Run:
```
static-bind ip-address ip-address mac-address mac-address option-template template-name
```
    A DHCP Option template is bound to static clients.

Configuring User-defined Options for Clients

Context

Vendors can define DHCP options. A device functioning as a DHCP server can allocate vendor-defined network parameters to clients using the following methods:

Based on the options in DHCP Discovery messages: Options are configured using the dhcp server option (based on an interface address pool) or option (based on a global address pool) command. The device provides options only when requested by clients.
By forcibly appending the Options field: Options are configured using the dhcp server force insert option (based on an interface address pool) or force insert option (based on a global address pool) command. The device inserts the Options field to DHCP Reply messages, regardless of whether the options are requested by clients.

Procedure

Configure user-defined options for clients based on an interface address pool.

Run:
```
system-view
```
The system view is displayed.
(Optional) Run:
```
dhcp server trust option82
```
The DHCP server is enabled to trust Option 82.
By default, the device is enabled to trust Option 82.
The Option 82 field is called the DHCP relay agent information field. It records the location of a DHCP client, based on which a DHCP server can select address allocation policies including IP addresses and other network parameters. Vendors can define Option 82 based on their requirements. Currently, a device functioning as the DHCP server cannot allocate network parameters to clients based on policies. After the device is enabled to trust Option 82, the device normally allocates IP addresses to clients. If the device is disabled from trusting Option 82, the device discards received messages carrying Option 82.

Run:

interface interface-type interface-number [.subinterface-number ]

The interface view or sub-interface view is displayed.

(Optional) Run:
```
dhcp server force insert option  code &<1-254>
```
The DHCP server is configured to forcibly insert an Option field to DHCP Reply messages sent to DHCP clients.
By default, the DHCP server does not forcibly insert an Option field to DHCP Reply messages.
After this function is configured, the device inserts an Option field to a DHCP Reply message regardless of whether the option has been requested.

Run:

dhcp server option code [ sub-option sub-code ] { ascii ascii-string | hex hex-string | cipher cipher-string | ip-address ip-address &<1-8> }

DHCP options are configured.

By default, no option is configured.

NOTE:

If an option carries a password, using ascii or hex is insecure. Using cipher is recommended. For security purposes, the password must be at least six characters long and contain at least two of the following: digits, lowercase letters, uppercase letters, and special characters.

After an option is configured, the device provides this option only when requested by clients.

Some options are configured using other commands, as described in the following table.

Table 3-9 Commands for configuring options

Option	Configuration Command	Description
Option1	mask-length in the ip address ip-address { mask \| mask-length } command	Specifies the subnet mask.
Option3	ip-address in the ip address ip-address { mask \| mask-length } command	Specifies the gateway address.
Option6	dhcp server dns-list ip-address &<1-8>	Specifies the DNS server IP address.
Option15	dhcp server domain-name domain-name	Specifies the domain name.
Option44	dhcp server nbns-list ip-address &<1-8>	Specifies the NetBIOS server IP address.
Option46	dhcp server netbios-type { b-node \| h-node \| m-node \| p-node }	Specifies the NetBIOS node type.
Option50	Does not need to be configured on the DHCP server	Specifies the requested IP address.
Option51	dhcp server lease { day day [ hour hour [ minute minute ] ] \| unlimited }	Specifies the IP address lease.
Option52	Does not need to be configured on the DHCP server	Specifies the additional option.
Option53	Does not need to be configured on the DHCP server	Specifies the DHCP message type.
Option54	Does not need to be configured on the DHCP server	Specifies the server identifier.
Option55	Does not need to be configured on the DHCP server	Specifies the parameter request list.
Option57	Does not need to be configured on the DHCP server	Specifies the maximum length of a DHCP message.
Option58	Does not need to be configured on the DHCP server	Specifies the lease renewal time (T1), which is 50% of the lease time.
Option59	Does not need to be configured on the DHCP server	Specifies the lease renewal time (T2), which is 87.5% of the lease time.
Option61	Does not need to be configured on the DHCP server	Specifies the client identifier.
Option82	Does not need to be configured on the DHCP server	Specifies relay agent information.
Option121	dhcp server option121 ip-address { ip-address mask-length gateway-address } &<1-8>	Specifies a group of classless routes.
Option184	dhcp server option184 { as-ip ip-address \| fail-over ip-address dialer-string \| ncp-ip ip-address \| voice-vlan vlan-id }	Specifies voice parameters. NOTE: AR503GW-LM7, AR503GW-LcM7 do not support voice-vlan vlan-id parameter.

Run:
```
dhcp server option121 ip-address { ip-address mask-length gateway-address } &<1-8>
```
A classless static route allocated to a DHCP client is configured.
By default, no classless static route allocated to DHCP clients is configured.
Run:
```
dhcp server option184 { as-ip ip-address | fail-over ip-address dialer-string | ncp-ip ip-address | voice-vlan vlan-id }
```
Option 184 allocated to DHCP clients is configured.
By default, the Option 184 field is not configured.
NOTE:
AR503GW-LM7, AR503GW-LcM7 do not support voice-vlan vlan-id parameter.

Configure user-defined options for clients based on a global address pool.

In the global address pool view:

Run:
```
system-view
```
The system view is displayed.
(Optional) Run:
```
dhcp server trust option82
```
The DHCP server is enabled to trust Option 82.
By default, the device is enabled to trust Option 82.
The Option 82 field is called the DHCP relay agent information field. It records the location of a DHCP client, based on which a DHCP server can select address allocation policies including IP addresses and other network parameters. Vendors can define Option 82 based on their requirements. Currently, a device functioning as the DHCP server cannot allocate network parameters to clients based on policies. After the device is enabled to trust Option 82, the device normally allocates IP addresses to clients. If the device is disabled from trusting Option 82, the device discards received messages carrying Option 82.
Run:
```
ip pool ip-pool-name
```
The global address pool view is displayed.
(Optional) Run:
```
force insert option code &<1-254>
```
The DHCP server is configured to forcibly insert an Option field to DHCP Reply messages sent to DHCP clients.
By default, the DHCP server does not forcibly insert an Option field to DHCP Reply messages.

Run:

option code [ sub-option sub-code ] { ascii ascii-string | hex hex-string | cipher cipher-string | ip-address ip-address &<1-8> }

DHCP options are configured.

By default, no option is configured.

NOTE:

Some options are configured using other commands, as described in the following table.

Table 3-10 Commands for configuring options

Option	Configuration Command	Description
Option1	mask-length in the ip address ip-address { mask \| mask-length } command	Specifies the subnet mask.
Option3	gateway-list ip-address &<1-8>	Specifies the gateway address.
Option6	dns-list ip-address &<1-8>	Specifies the DNS server IP address.
Option15	domain-name domain-name	Specifies the domain name.
Option44	nbns-list ip-address &<1-8>	Specifies the NetBIOS server IP address.
Option46	netbios-type { b-node \| h-node \| m-node \| p-node }	Specifies the NetBIOS node type.
Option50	Does not need to be configured on the DHCP server	Specifies the requested IP address.
Option51	lease { day day [ hour hour [ minute minute ] ] \| unlimited }	Specifies the IP address lease.
Option52	Does not need to be configured on the DHCP server	Specifies the additional option.
Option53	Does not need to be configured on the DHCP server	Specifies the DHCP message type.
Option54	Does not need to be configured on the DHCP server	Specifies the server identifier.
Option55	Does not need to be configured on the DHCP server	Specifies the parameter request list.
Option57	Does not need to be configured on the DHCP server	Specifies the maximum length of a DHCP message.
Option58	Does not need to be configured on the DHCP server	Specifies the lease renewal time (T1), which is 50% of the lease time.
Option59	Does not need to be configured on the DHCP server	Specifies the lease renewal time (T2), which is 87.5% of the lease time.
Option61	Does not need to be configured on the DHCP server	Specifies the client identifier.
Option82	Does not need to be configured on the DHCP server	Specifies relay agent information.
Option121	option121 ip-address { ip-address mask-length gateway-address } &<1-8>	Specifies a group of classless routes.
Option184	option184 { as-ip ip-address \| fail-over ip-address dialer-string \| ncp-ip ip-address \| voice-vlan vlan-id }	Specifies voice parameters. NOTE: AR503GW-LM7, AR503GW-LcM7 do not support voice-vlan vlan-id parameter.

Run:
```
option121 ip-address { ip-address mask-length gateway-address } &<1-8>
```
A classless static route allocated to a DHCP client is configured.
By default, no classless static route allocated to DHCP clients is configured.
Run:
```
option184 { as-ip ip-address | fail-over ip-address dialer-string | ncp-ip ip-address | voice-vlan vlan-id }
```
Option 184 allocated to DHCP clients is configured.
By default, the Option 184 field is not configured.
NOTE:
AR503GW-LM7, AR503GW-LcM7 do not support voice-vlan vlan-id parameter.

In the DHCP Option template view:
1. Run:
```
system-view
```
  The system view is displayed.
2. Run:
```
dhcp option template template-name
```
  A DHCP Option template is created and its view is displayed.
  By default, no DHCP Option template is created on a device.
  To allocate network parameters (except IP addresses) to static clients, configure a DHCP Option template. Network parameters configured in the DHCP Option template view take effect only for static clients. If a network parameter is configured differently in the global address pool and DHCP Option template views, the configuration in the DHCP Option template view takes effect.
  To allocate IP addresses only to static clients (for details, see (Optional) Configuring a DHCP Server to Allocate Fixed IP Addresses to Specified Clients), you do not need to configure a DHCP Option template.
3. (Optional) Run:
```
force insert option code &<1-254>
```
  The DHCP server is configured to forcibly insert an Option field to DHCP Reply messages sent to DHCP clients.
  By default, the DHCP server does not forcibly insert an Option field to DHCP Reply messages.
4. Run:
```
option code [ sub-option sub-code ] { ascii ascii-string | hex hex-string | cipher cipher-string | ip-address ip-address &<1-8> }
```
  DHCP options are configured.
  By default, no option is configured.
  
  NOTE:
  If an option carries a password, using ascii or hex is insecure. Using cipher is recommended. For security purposes, the password must be at least six characters long and contain at least two of the following: digits, lowercase letters, uppercase letters, and special characters.
  Some options are configured using commands, as described in Table 3-10.
5. Run:
```
option121 ip-address { ip-address mask-length gateway-address } &<1-8>
```
  A classless static route allocated to a DHCP client is configured.
  By default, no classless static route allocated to DHCP clients is configured.
6. Run:
```
option184 { as-ip ip-address | fail-over ip-address dialer-string | ncp-ip ip-address | voice-vlan vlan-id }
```
  Option 184 allocated to DHCP clients is configured.
  
  NOTE:
  AR503GW-LM7, AR503GW-LcM7 do not support voice-vlan vlan-id parameter.
  By default, the Option 184 field is not configured.
  If you need to configure other items in the DHCP Option template view, complete them first before performing the following steps.
7. (Optional) Run:
```
quit
```
  Return to the system view.
8. (Optional) Run:
```
ip pool ip-pool-name
```
  The global address pool view is displayed.
9. (Optional) Run:
```
static-bind ip-address ip-address mac-address mac-address option-template template-name
```
  A DHCP Option template is bound to static clients.

What is the DHCP option for DNS?

DHCP option 81: Client Fully Qualified Domain Name – this option allows to perform automatic update of the DNS records associated to the client, mainly the A and PTR. In the option we can specify whether the client or the server will update the records and the FQDN associated to the client.

Which DHCP client option is used to provide a list of IP addresses for DNS servers?

For example, DHCP option 3 is used to list the available routers in the network of the client and option 6 is used to list the available DNS servers.

How does a DHCP server respond to an IP request that can't be renewed?

Note If a client requests an invalid or duplicate address for the network, a DHCP server can respond with a DHCP denial message (DHCPNAK packet). This forces the client to release its IP address and obtain a new, valid address.

What RFC defines the DNS resource record types?

It uses the same format as the DS record. This record type is defined in RFC 4431. The DNSKEY record specifies the DNSSEC key record. A zone signs its authoritative RRsets by using a private key and stores the corresponding public key in a DNSKEY RR.