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In addition to an IP address, you can specify various DHCP parameters to be offered to DHCP clients such as default gateways and DNS domain names. You can configure DHCP parameters on a per-node basis or on a per-subnet basis.
To define DHCP parameters, do the following:
$ dhcpgui |
To define BOOTP parameters or parameters for statically addressed DHCP clients, select the Node tab.
This is the minimum information needed to configure MAC-to-IP address
mapping. Depending on your site requirements, you may need to specify
additional parameters such as netmask, default routers, and DNS servers.
7.3 Defining Client Information Using the GUI
This section explains how to use the DHCP GUI to define client information on the DHCP server.
For information about how to define DHCP client information manually by
editing configuration files and updating binary databases, see
Section 7.4.
7.3.1 Using the Configuration Window
Tabs across the top of the DHCP server configuration window represent categories of parameters you set to configure computers on your network.
The tabs are described as follows:
| Tab | Function |
|---|---|
| Server/Security | Defines the server configuration (see Section 7.8.1). You can set your IP address ranges, general server parameters, or view currently leased IP addresses and their lease time. |
| Subnets | Assigns client configurations for entire subnets. |
| Nodes | Adds and customizes specific machines on your network, usually for BOOTP clients. |
| Groups | Defines a group of settings for predefined collections of machines. |
Choose a tab for the category of parameters you want to configure. The window for each tab has three columns.
The left column lists the items that are configured for that category. The list always contains a [New Record] item to configure another machine. Choose an item from this list to enter or view its parameters.
The middle column lists the available parameters for the selected item along with the current specification or setting. Choose a parameter to enter or change the specification or setting.
To add or change a parameter setting, select a parameter and enter the value for the parameter in the field to the right. You can enter values as:
When there is more than one value field, press Tab to move to the next
field. To delete information in a field, select the text, then click
Delete.
7.3.1.1 Saving Information in a Record
If you add or revise information in a field, you need to save the information using one of the following methods:
For some subjects, you can add more than one record. To add a new record:
When only one record is possible, [New Record] disappears after you
configure the first server.
7.3.1.3 Saving the Changes
To exit the GUI and save the changes you made:
By editing DHCP configuration files and updating binary databases, you can define DHCP client information manually instead of using the DHCP GUI.
For information about how to define DHCP client information manually,
see Section 7.4.
7.5 Setting Up a DHCP Cluster Failover Environment
You can set up a cluster environment for DHCP server failover in which a standby system becomes the DHCP server if the active DHCP server process crashes or is stopped, or the system on which it is running crashes or shuts down.
With cluster failover, the DHCP server uses the OpenVMS lock manager during process initialization to acquire a system-level, exclusive-mode lock on a resource called TCPIP$DHCP_SERVER. When a packet is broadcast to the DHCP server port, the packet is received on each of the cluster nodes on which DHCP has been configured and a DHCP server process is created. One DHCP server process obtains the lock on TCPIP$DHCP_SERVER and becomes the active DHCP server, while the other DHCP servers become the standby servers.
When the active DHCP server process exits for any reason, the lock on TCPIP$DHCP_SERVER is released. One of the standby processes acquires the lock, then exits to flush the buffers. The next incoming BOOTP/DHCP packet causes a new process to be created, and the lock assignment process begins again.
To configure the DHCP server failover environment, do the following:
$ CREATE/DIRECTORY/OWNER=TCPIP$DHCP WORK1$:[DHCP_CONFIG] |
$ DEFINE/SYSTEM TCPIP$DHCP_CONFIG WORK1$:[DHCP_CONFIG] |
$ dhcpsigterm |
$ COPY SYS$SYSDEVICE:[TCPIP$DHCP]DHCPCAP. TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]DHCPTAGS. TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]NAMEPOOL. TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]NETMASKS. TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]NETS. TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]SERVER.PCY TCPIP$DHCP_CONFIG: $ COPY SYS$SYSDEVICE:[TCPIP$DHCP]DB%.%%% TCPIP$DHCP_CONFIG: |
$ DIRECTORY/SECURITY WORK1$:[DHCP_CONFIG] $ DIRECTORY/SECURITY WORK1$:[000000]DHCP_CONFIG.DIR |
$ CREATE/DIR SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ PURGE SYS$SYSDEVICE:[TCPIP$DHCP] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]DHCPCAP.;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]DHCPTAGS.;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]NAMEPOOL.;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]NETMASKS.;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]NETS.;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]SERVER.PCY;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] $ RENAME SYS$SYSDEVICE:[TCPIP$DHCP]DB%.%%%;* SYS$SYSDEVICE:[TCPIP$DHCP.SAVE] |
17.18.0.0 17.18.208.100 17.18.208.10-17.18.208.50 |
17.18.0.0 0.0.0.0 17.18.208.10-17.18.208.50 |
If you specified automatic startup during the TCP/IP Services configuration procedure (TCPIP$CONFIG), the DHCP server process starts automatically when a DHCP packet arrives at port 67.
If you want to stop the DHCP server process (which remains stopped until the next DHCP packet arrives), enter the following utility command as defined in TCPIP$DHCP_SETUPCOMMANDS.COM:
$ dhcpsigterm |
Because the DHCP server has several binary databases open (updates to
which might not have been flushed to the disk), do not stop a running
DHCP process using the DCL command STOP/ID=entry_number.
Instead, stop the DHCP process by entering the dhcpsigterm
command.
7.7 Shutting Down and Restarting the DHCP Service
To shut down DHCP, enter the following command:
$ @SYS$MANAGER:TCPIP$DHCP_SHUTDOWN |
To restart DHCP, enter the following commands:
$ @SYS$MANAGER:TCPIP$SERVICE_SETUP DHCP $ TCPIP ENABLE SERVICE DHCP |
You can modify the default DHCP server settings and define additional characteristics as follows:
| Task | Go to... |
|---|---|
| Define server and security parameters. | Section 7.8.1 |
| Define subnet parameters. | Section 7.8.2 |
| Define node parameters. | Section 7.8.3 |
| Define group parameters. | Section 7.8.4 |
| Define systemwide logical names. | Section 7.8.5 |
Use the GUI to set up the configuration of a DHCP server. Use the Server/Security tab to :
To configure the server parameters using the Server/Security tab of the GUI:
$ dhcpgui |
You can change any or all of the Server/Security parameters described in this section.
Accept Client Name
Specifies if the server assigns names to client machines according to a policy that is established on the server by the system manager.Even when this capability is enabled, the server ignores the client-suggested name if it is already in use by another client in the same domain.
If the server is unable to find a name for the client by applying this policy, it will:
False: Assign a name from the pool. Default. True: Use the name the client suggests for itself, if specified. Assign Name by Hardware Addr
Specifies if you can assign host names by the hardware address. If you choose true, the client computer always has the same name, even if its IP address changes; however, to do so, the client must remain in the same domain.This option is appropriate for sites supporting dynamic updating of the name service. When you select this policy, the server maintains a binding of the client's unique identifier to the name the client first acquires.
Note
Local and DNS do not support dynamic updating of the name service. Therefore, Compaq recommends that you assign names by IP address by setting the Assign Name by IP Addr parameter.If the name service does not dynamically update, the new name-IP address mapping implied by this policy is not available to other clients until you bring the name service up to date by another mechanism. This means dumping data from the database and using it to update the name service manually.
False: Disable assignment of host names by hardware addresses. Default. True: Enable assignment of host names by hardware addresses. Use the naming method defined in the NAMEPOOL. file. Assign Name by IP Addr
Specifies if you can assign host names by an IP address. If you choose True, the client receives its name from the name service as a result of a gethostbyaddr routine call. Also, when a client computer moves, it can receive a new name from the name service.
False: Host names cannot be assigned by IP addresses. The DHCP server does not issue a gethostbyaddr routine call. Instead, the session uses the naming method defined in the NAMEPOOL. file. True: Host names can be assigned by IP addresses. Default. Auto Release Old Lease
Set this to True if you want to automatically delete leases when the client changes its network. For example, if the client:
- Receives an address on Subnet A
- Then moves to Subnet B
The server releases the leased IP address on Subnet A even though the leased IP address on Subnet A is still valid. The default setting is False.
Auto Reread Config File
Instructs the server to see if the DHCPCAP. file has changed, indicated by the timestamp. This occurs each time a client requires a configuration. If the file changes, the server re-reads and re-parses the DHCPCAP. file.The default is True.
Auto Synchronize Database
Choose True to flush the server database to disk after each update. This makes the server more reliable if there is a failure such as a system crash or unintentional power shutdown. Setting this parameter to True can slow down the server. The default is False.BOOTP Addr From Pool
Specifies if the DHCP server does not require a preestablished binding. When none exists, the server allocates an address from the pool to the client. Because BOOTP does not understand the concept of lease times, all such allocations are permanent regardless of the lease times specified elsewhere in the database.When you disable BOOTP Addr From Pool, the Server only supports BOOTP clients whose IP address is configured into the database. This means the binding of the IP address to the client must be preestablished using the identical method to BOOTP. The address must be consistent with the network to which the client is attached.
False: Do not pick an address from a pool. Requires a preestablished binding. Default. True: Pick an address from a pool. Does not require a preestablished binding. BOOTP Client Lease Extension
When you set this parameter to a value above zero, the server grants Finite leases to BOOTP clients. BOOTP clients do not know this, so before the server can reuse these leases, it must ping the IP address. If the server hears a reply, it extends the lease by the time interval specified by this parameter (in seconds).The default value is 0 seconds.
Note
This capability is relevant only to BOOTP clients that are dynamically addressed; that is, "BOOTP_addr_from_pool" is set to True.BOOTP Compatibility
Choose True to have the server act as a BOOTP server instead of a DHCP server when the client requests a BOOTP address.
False: The server should act as a DHCP server only. True: The server should also act as a BOOTP server. Default. Check BOOTP Client Net
Before a BOOTP client is given a hard-wired IP address, the server makes sure that the client is connected to the logical IP network for which the address is valid. If the client is not connected, the server logs an error and does not send a response to the client.For this to work properly, the NETMASKS. file must contain the network numbers and masks for any non-standard IP Class A, B, or C configuration.
False: Do not check the IP network of the address. Default. True: Check the IP network of the address. Canonical Name
Overrides the value normally returned by a gethostname routine call (default). Primarily used for multihomed hosts with a canonical name corresponding to an interface that is not recognized by the JOIN software (for example, ATM interfaces) and for high-availability servers that have per-service IP addresses that differ from a physical IP host address.
False: Use the host name returned by a gethostname routine call. Default. True: Use the specified canonical host name. Default Lease Time
Specifies the value used on all leases for clients that have no other value explicitly configured. Enter the lease time of the IP address granted to a client.The default lease time is one day.
Free List Size
Specifies the size of the internal array specifying the number of address blocks held on the free list. If this number is too high, the server will lose previous allocations of expired leases quickly. If this number is too low, performance may suffer. The default setting is 8.Min BOOTP Packet Size
Specifies the minimum packet size for DHCP requests. Change this value to allow the Server to work with some non-compliant DHCP clients that send DHCP requests smaller than the minimum required packet length.The default minimum packet size is 300 bytes.
Expand BOOTP Packet
Expands the BOOTP reply packet to 548 bytes. Applies to BOOTP clients only.
False: All replies to BOOTP clients are 300 octets or a size equal to the size of the packet received, whichever is larger. Default. True: All replies to BOOTP clients are expanded to 548 bytes. Name Service
Specifies the implementation of the underlying name service. Name service authenticates, routes, addresses, and performs naming-related functions for other computers on the network. DNS is the only name service available with TCP/IP Services.Name Service Updatable
Not applicable for TCP/IP Services. DNS cannot be updated.Ping BOOTP Clients
Before the DHCP server assigns an IP address to a BOOTP client, the server checks to see if the address is available by using ping to send an Internet Control Message Protocol (ICMP) echo request. If the server receives a reply, it logs an error. Then:
- If the address was from the dynamic pool, the server marks it as unavailable, and selects a new address from the pool.
- If the address was statically configured, the server refuses to configure the client.
False: Do not send an ICMP echo request to a BOOTP client before assigning an IP address. Default. True: Send an ICMP echo request to a BOOTP client before assigning an IP address. Ping Timeout
Specifies the time (in milliseconds) of the ping timeout. Enter the amount of time the server is to wait before concluding no other host is using the IP address. After the timeout, the ping command stops checking.If you do not want the server to ping before giving out an IP address, set the timeout value to 0. The default is 500 milliseconds.
Provisional Time To Live
Specifies the maximum time period that an IP address can remain on the provisionally allocated list before it can be allocated to another client. The value should be limited to a few minutes. The default is 1 minute.Reply to Relay On Local Net
Specifies whether the server ignores packets forwarded to it from a relay agent on the same subnet as the server
False: Do not reply (the server should hear the client broadcast directly). Default. True: Reply no matter where the agent is located (the value in giaddr field). Restrict to Known MAC Addresses
Specifies whether to restrict IP addresses that are assigned to a matching MAC address. When specified, you can manually assign a MAC address. This parameter indicates whether the server should respond to clients with a MAC address that is unknown to the server.Choose true to have the server provide DHCP information to only those hosts that have a known MAC address. To register a known MAC address client, use Preload MAC Addresses feature from the Server/Security tab. Choose False to have the server provide DHCP information to all clients.
False: Do not allow manual assignment of MAC addresses. Default. True: Allow manual assignment of MAC addresses. Send Options in DHCP Offer
Specifies if the server is to send a complete configuration to a DHCP client. Resolving a client configuration can be time consuming. In a multiserver environment, the client can select another server.
False: Send a minimum configuration. Default. True: Send a complete configuration. Support Microsoft RAS Server
Specifies support for the Microsoft Proxy Remote Access Server (RAS). The RAS server generates a BOOTP packet with a MAC address of 16 octets.
False: Ignore a BOOTP packet with a MAC address of 16 octets. Default. True: Recognize a BOOTP packet with a MAC address of 16 octets. Use MAC addr as client ID
Specifies if the server is to use the client ID to uniquely identify a client. If set to True, the server uses the client's MAC address as the client ID. BOOTP also uses the MAC address to uniquely identify a client.
False: Use Client ID to identify clients. Default. True: Use MAC address to identify clients.
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