Setting the Server Identifier DHCP Service option - BlueCat Integrity - 26.1.0

Address Manager Administration Guide
ft:locale
en-US
Product name
BlueCat Integrity
Version
26.1.0

If you have configured two or more IP addresses on a single interface, the wrong server ID might be delivered to DHCP clients. Unless a custom server ID is configured as a DHCP Service option, the DNS/DHCP Server will send clients the server ID matching the first IP address configured on the service interface. This behavior forces DHCP clients to learn the DHCP server IP address that may not match the IP subnet of address lease they obtained. As such, the client won't be able to send DHCP unicast packets back to DHCP server.

Example:

A DNS/DHCP Server has the service interface eth0.150 that communicates with VLAN 150. Three IP addresses are assigned to interface eth0.150 as follows: 10.10.150.1/24, 172.30.150.1/24, and 192.0.2.1/24. The address 10.10.150.1/24 is the first IP address on the interface. If you deploy DHCP range 172.30.150.10-172.30.150.20, then the DNS/DHCP Server will properly serve DHCP from the interface eth0.150. However, DHCP clients will receive 10.10.150.1 as their Server ID, which doesn't match subnet 172.30.150.0/24. Therefore the client-obtained dynamic IP address 172.30.150.14 will believe its DHCP server is 10.10.150.1 (when it should be 172.30.150.1). This client won't be able to send unicast DHCP packets back to the DHCP server; it won't be able to send a DHCP renew request for an existing address lease or inform the DHCP server of release events for that lease.

You must deploy a Server Identifier DHCP Service option at the network level to ensure that the IP address sent to clients properly indicates the address of the interface that handled the request.

To set the Server Identifier DHCP Service option:

  1. Navigate to the DHCP range that you will be applying the server identifier option to. Navigate to a DHCP range by selecting a range in the IPv4 DHCP ranges tab of an IPv4 network.
  2. Select the Deployment options tab.
  3. Select New > DHCPv4 Service option.
  4. Under General, select the option and set its parameters:
    • Name—select Server Identifier (18) from the drop-down menu.
    • IPv4 address—enter one of the IP addresses assigned to the server in the Address field.
  5. On the Servers tab, select the servers or server group to which the option applies:
    • All servers—applies the deployment option to all servers in the configuration.
    • Server group—applies the deployment option to a specific server group in the configuration. Select a server group from the drop-down list.
      Attention: You cannot configure DHCP deployment options on a multi-primary server group.
    • Server—applies the deployment option to a specific server in the configuration. Select a server from the drop-down list.
      Attention: You cannot configure DHCP deployment options on servers that are part of a multi-primary server group.
    Note: You can't override deployment options set at the configuration level from the server group level if the deployment option is applied to a specific server within a server group.
  6. In the Change control section, add comments if required.
  7. Select Create or Create and add another.
  8. Deploy DHCP to apply the changes.