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Once you have made changes to the configuration files, you must force the server to read them again by sending it an HUP signal (see Section 7.3.1). Enter the following command:
$ DHCPSIGHUP |
The commands you use to modify and look at the contents of the DHCP databases are described in Table 7-10. TCP/IP Services supplies UNIX type commands for users familiar with the JOIN implementation of a DHCP server.
| DHCP GUI | OpenVMS Command | UNIX Command | Description |
|---|---|---|---|
|
Active IP Snapshot
Add/Delete |
DHCPDBMOD | jdbmod | Modifies lease and naming information in the database. Allows you to preassign static IP addresses to clients. Also allows you to create, delete, or modify existing entries. |
| Preload MAC Addresses | DHCPDBREG | jdbreg | Populates the database with MAC addresses of known clients. Each record to be loaded is terminated by a new line, and the fields within each record are separated by the vertical bar (|) character. |
| DHCPDBDUMP | jdbdump | Reads and outputs information stored in the lease database files including MAC address information, IP addresses, and lease information. Each line of output describes the lease information for one client. | |
| Active IP Snapshot | DHCPSHOWDBS | SHOWDBS | Reads the same information described for DHCPDBDUMP , except that the output is in a format that is easier to read. |
| DHCPDBSHOW | DBSHOW | Displays the contents of a single DHCP binary database. |
For information about how to enter the DHCP utility commands, see
Sections 7.8.1 through 7.8.3.
7.8.1 Using the DHCPDBDUMP, DHCPSHOWDBS, and DHCPDBSHOW Utilities
The DHCPDBDUMP , DHCPSHOWDBS , and DHCPDBSHOW commands dump the information stored in the lease database files. The dumped lease information includes:
Each line of output describes the lease information for one client. The output is in a format that is used by the DHCPDBMOD utility to modify the lease database.
The DHCPBDUMP , DHCPSHOWDBS , and DHCPDBSHOW commands perform read operations on the database, while DHCPDBMOD performs write operations. |
The DHCPDBDUMP , DHCPSHOWDBS , and DHCPDBSHOW commands accept a number of different flags and arguments. Table 7-11 lists some of the more important flags.
| Flag | Description |
|---|---|
| -a | Dumps dates in readable format. |
| -c | Dumps currently active leases only. |
| -e | Dumps expired leases only. |
The following examples show typical output from the DHCPSHOWDBS , DHCPDBSHOW , and DHCPDBDUMP commands:
$ DHCPSHOWDBS IP address Owner Expires Granted on Last mod ified client id 10.10.2.100 10.10.2.6 01/28/2000 13:50 01/28/2000 13:30 01/28/2000 13:30 0 01:08:00:2b:e5:2c:44 10.10.2.101 10.10.2.6 01/28/2000 13:52 01/28/2000 13:32 01/28/2000 13:32 0 01:08:00:2b:bf:7d:bb 10.10.4.100 10.10.2.5 01/21/2000 09:27 01/21/2000 09:07 01/21/2000 09:07 0 01:08:00:2b:e5:2c:44 IP address Name 10.10.2.101 gody.compaq.com. 10.10.2.100 sarek12.compaq.com. $ DHCPDBSHOW a IP address owner expires granted on la st modified network client id 10.10.2.101 10.10.2.6 02/14/2000 11:18:10 02/14/2000 10:58:10 02 /14/2000 10:58:10 10.10.2.0 0,7,01:08:00:2b:e5:2c:44 10.10.2.103 10.10.2.6 02/14/2000 11:08:21 02/14/2000 10:48:21 02 /14/2000 10:48:21 10.10.2.0 1,6,08:00:2b:2a:de:1e 10.10.2.100 10.10.2.6 02/14/2000 11:14:23 02/14/2000 10:54:23 02 /14/2000 10:54:23 10.10.2.0 0,7,01:08:00:2b:bf:7d:bb 10.10.4.100 10.10.2.5 01/21/2000 09:27:26 01/21/2000 09:07:26 01 /21/2000 09:07:26 10.10.4.0 0,7,01:08:00:2b:e5:2c:44 10.10.2.104 10.10.2.6 02/14/2000 11:09:33 02/14/2000 10:49:33 02 /14/2000 10:49:33 10.10.2.0 1,6,08:00:2b:2a:de:a8 Record count = 5 |
$ DHCPDBDUMP 01:08:00:2b:e5:2c:44|0|7|10.10.2.100|949084208|949085408|949084808|949084208| 10.10.2.6|sarek12|compaq.com| 01:08:00:2b:bf:7d:bb|0|7|10.10.2.101|949084349|949085549|949084949|949084349| 10.10.2.6|gody|compaq.com| 01:08:00:2b:e5:2c:44|0|7|10.10.4.100|948463 |
The DHCPDBMOD command modifies the lease and naming information in the database files. It allows the user to create, delete, or modify existing database entries and to preassign static IP address to clients.
The utility takes input from a file that describes various entries in the database. The syntax of each entry is similar to the output of DHCPDBDUMP .
Use the following format:
Example 7-11 shows a sample entry. The first entry describes the client called alpha.acme.com with the IP address 143.32.3.20.
The second entry describes a Microsoft DHCP client with the IP address 143.32.3.21. No name is given for this client.
| Example 7-11 Sample DHCPDBMOD Entry |
|---|
$ DHCPDBMOD 00:a0:24:8c:6b:09(1)|1(2)|6(3)|143.32.3.20(4)|844989457(5)|844989466(6)|844989466(7)|844989466 (8) |143.32.3.1(9)|alpha(10)|acme.com(11)| 01:00:40:05:14:df:11|0|7|143.32.3.21|844989457|844989466|844989466|844989466 |143.32.3.1||| |
Although some fields can be empty, each entry consists of the following fields:
The DHCPDBMOD command accepts a number of different flags and arguments. Table 7-12 shows some of the more important flags.
| Flag | Description |
|---|---|
| -d | Deletes the record. |
| -e | Stores the record even if the lease has expired. |
| -l | Stores the lease information only. Does not store name information. |
| -n | Stores the name information only. Does not store lease information. |
| -w | Overwrites the record if a record already exists. |
By default,
DHCPDBMOD
stores both lease and name information for nonexpired and new clients.
7.8.3 Using the DHCPDBREG Utility
Use the DHCPDBREG command to populate the database with the MAC address of known MAC clients. Set the SERVER.PCY parameter Restrict to Known MAC Address to True to use this utility. The DHCPDBREG command can add or remove hosts from the list of known MAC addresses. Use the following syntax when you enter a record:
Each entry contains the following three fields:
The DHCPDBREG command accepts a number of different flags. Two of the most important flags are as follows:
| Flags | Description |
|---|---|
| -d | Deletes the record. |
| -s | Displays all registered MAC addresses. |
If the DHCP log file contains the message: "network not administered by server" and you use class A, B, or C IP addressing, check the NETMASKS. file to see that you have entered the netmask correctly for the subnet.
DHCP client is the TCP/IP Services component which allows a system to request network configuration information from a DHCP server and then use that information to configure one or more of its network interfaces.
TCP/IP Services DHCP client is an OpenVMS implementation of the Compaq Tru64 UNIX client.
This chapter reviews key concepts and describes the following topics:
When a system connects to a network, in addition to the appropriate network software, it must have configuration information that identifies the system in network communications. As a minimum, it must have an IP address, a broadcast address, and a subnet mask configured before any communication with other systems can take place. This information can be statically configured, that is, permanently stored in a local database and used every time the network is initialized. Or it can be dynamically configured by obtaining the information from a DHCP server during network initialization. The DHCP server maintains the configuration information, and upon a client request for such information, returns the configuration for that particular host through a client and server dialog using the DHCP protocol.
A system can have more than one network interface installed and you can use DHCP client to dynamically configure all or a subset of the installed interfaces. There is one DHCP client process running on a system and it configures all interfaces that are designated as under DHCP control.
In an OpenVMS Cluster, you can use DHCP client to configure one of the systems, a mix of systems or all systems in the cluster. Each system in the cluster using DHCP to configure its interfaces, must run DHCP client.
If a system is running DHCP client, it can not also run a DHCP server. |
Some of the parameters that are configurable by DHCP are interface specific. Examples of interface-specific parameters are the IP address and subnet mask. Most DHCP configurable parameters, however, are systemwide configurable parameters. Examples of systemwide parameters are the host name and DNS domain name.
The TCP/IP Services DHCP client supports controlled configuration of systemwide configurable items by designation of what is called the primary interface. The primary interface is the interface on which the DHCP client will use systemwide parameters received from the DHCP server to configure the system. Systemwide parameters received on an interface that is not designated primary will not be configured on your system by the DHCP client. There may be only one interface on a system that is designated as the primary DHCP interface, but you are not required to have any interface designated as the primary interface.
For example, if a system has multiple interfaces under DHCP control and the system receives a different host name from a DHCP server on each of the DHCP controlled interfaces, DHCP client uses the host name it receives on the primary interface to configure the host name for the client.
If a system has multiple interfaces and only one is under DHCP control, you can configure the systemwide parameters manually.
DHCP client uses the following rules to resolve conflicts:
Systemwide parameters are configured for a system as the last part of processing the final message (a DHCPACK protocol message) from the DHCP server. DHCP client, first configures the interface's IP address, subnet mask, and broadcast address; then, if the interface is designated as the primary interface, DHCP client configures the systemwide parameters.
See Table 8-2 for a list of the DHCP configurable parameters
supported by the TCP/IP Services DHCP client.
8.1.2 Requesting a Lease
A DHCP server allocates IP addresses to clients on a temporary or permanent basis. This time period is called a lease. A client can request a lease for some period of time, which the DHCP server can either honor or assign a different time period depending on the policy in force. A client may request a lease for an infinite period of time, but the server may choose to give out a lengthy but not infinite lease. For whatever time period the DHCP server assigns, the DHCP server guarantees not to reassign the IP address to any other system until the lease expires.
Lease times are represented in DHCP dialogs as relative time to be
interpreted with respect to the client's clock. If there is drift
between the client's clock and the server's clock, the server may
consider the lease expired before the client does. To compensate, the
server may return a shorter lease duration to the client than the
server commits to its local database of client information.
8.1.3 Requesting Parameters
The first service provided by a DHCP server is to provide storage of
network parameters for network clients. DHCP clients can query the DHCP
server to retrieve the configuration parameters. In its initial
discover or request message, a client can supply a list of parameters
for which it needs information. If the server does not return any or
all of the values for the requested parameters, the client uses default
values for any missing values.
8.1.4 Understanding How the DHCP Client Operates
When your system has an interface configured under DHCP control, the following sequence of steps occur at TCP/IP Services startup time:
$ TCPIP START COMMUNICATION/INITIALIZE |
DHCPCONF -W 30 ifname START |
DHCPCONF -P -W 30 ifname START |
The section describes the software and system elements that comprise DHCP client including:
Three programs comprise the DHCP client component:
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