Verifying a DHCP Server Configuration

To verify a DHCP server configuration, perform the following tasks:

Purpose

Verify the configuration of a DHCP server.

Action

From the J-Web interface, select Configuration>View and Edit>View Configuration Text. Alternatively, from configuration mode in the CLI, enter the show system services dhcp command from the top level.

You can also view the IP address pool from the CLI in operational mode by entering the show system services dhcp pool command.

Sample Output

What it Means

Verify that the output shows the intended configuration of the DHCP server. For more information about the format of a configuration file, see the J-series Services Router Configuration Guide.

Purpose

Verify that the DHCP binding database reflects your DHCP server configuration.

Action

From operational mode in the CLI, to display all active bindings in the database, enter the show system services dhcp binding command. To display all bindings in the database, including their current binding state, enter the show system services dhcp binding detail command. To display more information about a client, including its DHCP options, enter the show system services dhcp binding ip-address detail command, replacing ip-address with the IP address of the client.

The DHCP binding database resulting from the configuration defined in Configuring the DHCP Server with a Configuration Editor is displayed in the following sample output.

To clear the DHCP binding database, enter the clear system services dhcp binding command. To remove a specific entry from the DHCP binding database, enter the clear system services dhcp binding ip-address command, replacing ip-address with the IP address of the client.

You can also use the J-Web interface to view information in the DHCP binding database. For more information, see Monitoring DHCP.

Sample Output

IP Address   Hardware Address   Type          Lease expires at
192.168.2.2  02:04:06:08:0A:0C  dynamic       2005-02-07 8:48:59 PDT
192.168.2.50 01:03:05:07:09:0B  static        never

    IP address           192.168.2.2
    Hardware address     02:04:06:08:0A:0C
    Pool                 192.168.2.0/24
    Request received on  fe-0/0/0

Lease information:
    Type                 DHCP
    Obtained at          2005-01-24 8:48:59 PDT
    Expires at           2005-02-07 8:48:59 PDT
    State                active

DHCP options:
    Name: domain-name, Value: mycompany.net mylab.net
    Name: name-server, Value: 192.168.10.2
    Code: 16, Type: ip-address, Value: 192.168.2.33

What it Means

Verify the following information:

• For each dynamic binding, verify that the IP address is within the range of the configured IP address pool. Under Lease Expires, verify that the difference between the date and time when the lease expires and the current date and time is less than the maximum configured lease time.
• For each static binding, verify that the IP address corresponds to the MAC address displayed under Hardware Address (as defined in the static-binding statement in the configuration). Under Lease Expires, verify that the lease expiration is never.
• In the output displayed by the show system services dhcp binding ip-address detail command, verify that the options under DHCP options are correct for the subnet.
• Verify that the show system services dhcp conflict command does not display any conflicts.

Purpose

Verify that the DHCP server is operating as configured.

Action

Take the following actions:

• Use the ping command to verify that a client responds to ping packets containing the destination IP address assigned by the Services Router.
• Display the IP configuration on the client. For example, on a PC running Microsoft Windows, enter ipconfig /all at the command prompt to display the PC's IP configuration.

Sample Output

PING 192.168.2.2 (192.168.2.2): 56 data bytes
64 bytes from 192.168.2.2: icmp_seq=0 ttl=255 time=8.856 ms
64 bytes from 192.168.2.2: icmp_seq=1 ttl=255 time=11.543 ms
64 bytes from 192.168.2.2: icmp_seq=2 ttl=255 time=10.315 ms
...

Windows 2000 IP Configuration

        Host Name . . . . . . . . . . . . : my-pc
        Primary DNS Suffix  . . . . . . . : mycompany.net
        Node Type . . . . . . . . . . . . : Hybrid
        IP Routing Enabled. . . . . . . . : No
        WINS Proxy Enabled. . . . . . . . : No
        DNS Suffix Search List. . . . . . : mycompany.net
                                            mylab.net

Ethernet adapter Local Area Connection 2:

        Connection-specific DNS Suffix  . : mycompany.net mylab.net
        Description . . . . . . . . . . . : 10/100 LAN Fast Ethernet Card
        Physical Address. . . . . . . . . : 02-04-06-08-0A-0C
        DHCP Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.2.2
        Subnet Mask . . . . . . . . . . . : 255.255.254.0
        Default Gateway . . . . . . . . . : 192.168.10.3
        DHCP Server . . . . . . . . . . . : 192.168.2.1
        DNS Servers . . . . . . . . . . . : 192.168.10.2
        Primary WINS Server . . . . . . . : 192.168.10.4
        Secondary WINS Server . . . . . . : 192.168.10.5
        Lease Obtained. . . . . . . . . . : Monday, January 24, 2005 8:48:59 AM
        Lease Expires . . . . . . . . . . : Monday, February 7, 2005 8:48:59 AM

What it Means

Verify the following:

• The client returns a ping response.

  For information about using the J-Web interface to ping a host, see Using the J-Web Ping Host Tool. For more information about the ping command, see Pinging Hosts from the CLI or the JUNOS System Basics and Services Command Reference.

• The client IP configuration displayed contains the configured values. For example, for the DHCP configuration in Configuring the DHCP Server with a Configuration Editor, you can verify the following settings:
  • DNS Suffix Search List is correct.
  • IP address is within the IP address pool you configured.
  • DHCP Server is the primary IP address of the Services Router interface on which the DHCP message exchange occurs. If you include the server-identifier statement in your configuration, the DHCP server IP address specified in this statement is displayed.
  • Lease Obtained and Lease Expires times are correct.

  The ipconfig command also displays other DHCP client settings that can be configured on the Services Router, including the client's hostname, default gateways, and WINS servers.

Purpose

Display DHCP statistics, including lease times, packets dropped, and DHCP and BOOTP messages received and sent, to verify normal operation.

Action

Enter the show system services dhcp statistics command to display the DHCP statistics.

Sample Output

Packets dropped:
    Total                      0

Messages received:
    BOOTREQUEST                0
    DHCPDECLINE                0
    DHCPDISCOVER               0
    DHCPINFORM                 0
    DHCPRELEASE                0
    DHCPREQUEST               78

Messages sent:
    BOOTREPLY                  0
    DHCPOFFER                  0
    DHCPACK                   78
    DHCPNAK                    0

What it Means

Verify the following:

• The default settings displayed are consistent with your DHCP server configuration.
• The number of dropped packets and errors is small.
• DHCPREQUEST messages have been received and DHCPACK messages have been sent.