Installing and Administering Internet Services

258 Chapter6

Dynamic Host Conﬁguration Protocol (DHCP)

Dynamic Updates

DHCP can now dynamically update the DNS server. DHCP updates DNS

with the host name and IP address of the client. For every client DHCP

assigns a name and IP address to, it also adds an address record (“A”), a

pointer record (“PTR”), and a resource record (“RR”) of that client to the

DNS server.

To assign a name for every IP address, there is a new tag known as

“pcsn.” When this boolean tag is set, the DHCP server gives priority to

the name (if any) provided by the client. The name should be a fully

qualiﬁed domain name (FQDN). If it is not, then the DHCP server will

try appending the domain name (if set using "dn" tag) else it appends "."

and updates the DDNS.

Dynamic DNS Server Update Pre-Requisites

The dynamic DNS server has pre-requisites for accepting updates from

the DHCP server. These pre-requisites are used when DHCP server

updates (by either adding or deleting names and IP addresses) the DNS

server. DHCP supports and adheres to the following pre-requisites:

• The resource records (RR) should not exist for an add operation.

• The resource records must exist for a delete operation.

You can conﬁgure DHCPto ignore these pre-requisites by adding the “sp”

tag to the /etc/dhcptab conﬁguration ﬁle.

To enable dynamic updates, you must conﬁgure DHCP server along with

the DNS server. See the section “The BIND Conﬁguration File” on page

88 to conﬁgure the Name Server with the latest options and statements

needed to enable dynamic updates.

HP strongly recommends that DHCP servers and DNS server run on the

same machine for dynamic updates. See Figure 6-2 on page 259 for an

illustration of a single HP-UX host running both DHCP and DNS

servers. It shows each server and the daemons for each.