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SYSTEMS MANAGEMENT

The Domain Name System (DNS) is a database that

gives meaning to network domains and host names.

Name servers handle portions of the database called

zones, which correspond to the domains for which they

are responsible. The Dynamic DNS (DDNS) mechanism

allows data in a zone to be modified without reloading

zone data. This allows DNS data to be modified often, in

a timely manner, and with minimal overhead.

Without the DDNS mechanism, network host infor-

mation for zones is traditionally stored in static tables on

name servers. In such scenarios, system administrators

must edit these files by hand when a change needs to

be made, and then instruct the name server software

to reload the zones. If a network is primarily Dynamic

Host Configuration Protocol (DHCP) based and a static

DNS server is used for name registration and resolution,

manually updating the DNS database every time a remote

access controller (RAC) client receives a new IP address

typically involves a tremendous amount of time and effort,

even for a team of administrators. Using meaningful DNS

names that correspond to the names of RACs instead of the

controllers’ IP addresses can help make system administra-

tion organized and efficient.

Primary features of a DDNS updateBy default, a RAC DNS name is “RAC-ServiceTag,gg ” where

ServiceTag is the service tag of the managed server. Each g

RAC has configuration options to change the DNS name

and to overwrite the DNS domain name provided by the

DHCP server to a user-specified name. The default RAC

DNS name, username, and password appear on a sticker

on the controller.

BY PHIL WEBSTER AND BRIAN ZHANG

Dynamic DNS UpdatesUsing the Dell Remote Access Controller 4

The Dynamic Domain Name System (DDNS) update feature of the Dell Remote Access

Controller 4 (DRAC 4) dynamically modifies the Domain Name System (DNS) database.

This feature allows each remote access controller (RAC) IP address to be associated

with a meaningful DNS name so that administrators can connect to the RAC without

having to know the RAC IP address.

Related Categories:

Dell Remote Access Controller (DRAC)

Domain Name System (DNS)

Remote management

Systems management

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for the complete category index.

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A DDNS update modifies resource records (RRs) in the DNS serv-

er’s database. The affected RRs consist of the associated A (address)

record, which contains a mapping from a fully qualified domain name

(FQDN) to an IP address, and the associated PTR (pointer) record,

which contains a mapping from an IP address to a FQDN.

For example, the FQDN of a RAC named RAC1 in the domain

sales.company.com is RAC1.sales.company.com. When a DNS

update is enabled, the RAC registers the A record as well as the

PTR record with the DNS server.

A RAC DDNS update is triggered by the following: initial startup

of the RAC or modifying the IP address of the RAC. The DDNS

client resides on the RAC. The RAC can redirect DDNS requests

to another DNS server provided in the response from the primary

DNS server. Administrators can configure the DDNS feature via the

racadm utility, option ROM, or the main graphical user interface

(GUI) for the RAC.

DRAC 4 product requirements for DDNS updatesMany data centers choose to operate without DHCP. For this reason,

the Dell Remote Access Controller 4 (DRAC 4) default network con-

figuration is statically assigned, rather than defaulting to a DHCP

configuration. It is a DRAC 4 product requirement that DDNS

operate in a non-DHCP data center. This requires the DRAC 4

to directly issue the update commands to the DNS server, rather

than proxying through a DHCP server.

Nonsecure DDNS updatesBecause the secure DNS implementations provided by Microsoft®

Windows® and Linux® operating systems are incompatible, the

DRAC 4 uses nonsecure updates. It is a product requirement that

the DRAC 4 be able to operate in both Microsoft Windows–based

and Linux-based data centers.

DDNS proxying through a DHCP serverSome enterprise IT organizations prefer to have the DHCP server

perform the DDNS update to the DNS server, with the DHCP server

acting as a proxy. These organizations may enable secure DDNS

updates. However, when a secure DDNS update is enabled and a

DHCP server is used as a proxy, the DNS database is not secure.

This lack of security exists because DHCP is an unencrypted

and unauthenticated protocol. DHCP packets can easily be spoofed

by hackers. Adding the secure DDNS protocol on top of nonsecure

DHCP essentially means that the DNS database can be modified

by spoofed DHCP packets. Data center managers may be lured into

thinking that the DNS database is secure because they are using a

secure update but the DNS database is never secure when proxied

through the DHCP server.

In spite of the security risk involved, some organizations prefer

to use DHCP proxy updates. The DRAC 4 firmware version 1.40

allows administrators to configure DHCP proxy updates. The

following algorithm is used: If, and only if, cfgDNSRegisterRac

is 0 (false) and cfgNicUseDhcp f is 1 (true), the value of

cfgDNSRacName is included as the client-identifier option in the

DHCPREQUEST packet.

Configuration interfacesThe interfaces that can be used to configure the DDNS feature

of the DRAC 4 are the racadm utility, the out-of-band GUI, and

option ROM.

Racadm utilityThe following racadm parameters, which exist in the cfgLan-

Networking group, can be used to configure the DDNS feature

of the DRAC 4:

• CfgDNSServersFromDHCP: This Boolean object specifies

whether the RAC is retrieving DNS server addresses from the

DHCP server. It has a default value of 0 (false). • cfgDNSServer1: This specifies the IP address of the first

DNS server and has a default value of 192.168.0.5. This

parameter has meaning only when cfgDNSServersFromDHCP

is 0 (false). • cfgDNSServer2: This specifies the IP address of the second

fDNS server and has a default value of 192.168.0.6. A value of

0.0.0.0 may be entered if there is no second DNS server. This

parameter has meaning only when CfgDNSServersFromDHCP

is 0 (false). • cfgDNSRegisterRac: This Boolean object specifies whether

the RAC DNS name is being registered on the DNS server. It

has a default value of 0 (false). • cfgDNSRacName: This string specifies the RAC DNS name and

has a default value of “RAC-ServiceTag.” • cfgDNSDomainNameFromDHCP: This Boolean object specifies

whether the DNS domain name is being obtained from the

DHCP server. It has a default value of 0 (false). • cfgDNSDomainName: This string specifies the DNS domain

name and has a default value of “MYDOMAIN.” This param-

eter has meaning only when cfgDNSDomainNameFromDHCP is

0 (false).

Additionally, the cfgCurrentLanNetworking group has the fol-

lowing read-only parameters related to the DDNS feature:

• cfgDNSCurrentDhcpWasUsed: This Boolean object indi-

cates whether DHCP was used to obtain the DNS server IP

addresses. • cfgDNSCurrentServer1: This is the IP address currently

being used for DNS server 1.

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• cfgDNSCurrentServer2: This is the IP address

currently being used for DNS server 2. • cfgDNSCurrentDomainName: This is the DNS

domain name currently being used.

Out-of-band GUIThe following configuration options for the DDNS

feature appear on the Network Configuration page of

the DRAC 4 GUI (see Figure 1):

• “Use DHCP to obtain DNS server addresses”

check box: This is not checked by default. • “Static Preferred DNS Server” field: An IP

address is entered here; this field is used only

when the “Use DHCP to obtain DNS server

addresses” check box is not checked. • “Static Alternate DNS Server” field: An IP

address is entered here; this field is used only

when the “Use DHCP to obtain DNS server

addresses” check box is not checked. A value

of 0.0.0.0 may be entered if there is no alternate

DNS server. • “Register DRAC 4 on DNS” check box: This is not checked

by default. • “DNS DRAC 4 Name” field: The default value is

“RAC-ServiceTag.” • “Use DHCP for DNS Domain Name” check box: This is not

checked by default.

• “DNS Domain Name” field: This is used only when the “Use

DHCP for DNS Domain Name” check box is not checked.

The default value is “MYDOMAIN.”

Additionally, the System Summary page of the DRAC 4 GUI (see

Figure 2) has read-only settings for the DDNS feature which display

the current preferred DNS server, the current alternate DNS server,

the DNS DRAC 4 name, and the current DNS domain name. These

settings also specify whether DHCP is being used for DNS, whether

the DRAC 4 is registered on DNS, and whether DHCP

is being used for the DNS domain name.

Option ROM The following five fields in the “DNS Configuration

Options” section of the DRAC 4 option ROM utility (see

Figure 3) can be used to configure the DDNS feature:

“Servers from DHCP” option. This is a Boolean

toggle, which is toggled with the U key. The default

setting is “Disabled,” meaning that the two static DNS

server addresses are used. When the setting is changed

to “Enabled,” the DHCP server supplies the DNS server

addresses. If the “Use DHCP is” option in the “NIC

TCP/IP Configuration Options” section is set to “Dis-

abled,” the “Servers from DHCP” option cannot be set

to “Enabled,” and this field is grayed out.

“Static DNS Server 1” option. This is the IP

address of the first DNS server; it is modified with the

1 key. The default value is 192.168.0.5. If the “Servers

from DHCP” option is “Enabled,” this field cannot be

modified and is grayed out.Figure 1. Network Configuration page of the DRAC 4 GUI

Figure 2. System Summary page of the DRAC 4 GUI

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“Static DNS Server 2” option. This is the IP address of the

second DNS server; it is modified with the 2 key. The default value is

192.168.0.6. A value of 0.0.0.0 may be entered if there is no second

DNS server. If the “Servers from DHCP” option is “Enabled,” this

field cannot be modified and is grayed out.

“Register RAC Name” option. This is toggled with the C key

and the default setting is “Disabled.” When this option is not dis-

abled, this field displays the RAC DNS name. The default RAC DNS

name is “RAC-ServiceTag.” The RAC DNS name can be modified

only when toggling from the disabled state. Therefore, if this option

is not set to “Disabled,” administrators must press the C key twice

to modify the RAC DNS name.

“Static Domain Name” option. This is toggled with the F

key and the default value is “MYDOMAIN.” When this option

is not disabled, the static DNS domain name appears in the

field. The static DNS domain name can be modified only when

toggling from the disabled state. Therefore, if this option is not

set to “Disabled,” administrators must press the F key twice to

modify the static DNS domain name. (However, if the “Use DHCP

is” option is disabled, then the “Static Domain Name” option

cannot be set to “Disabled” and can be modified by pressing the

F key only once.) When the “Register RAC Name” option is set to

“Disabled,” this field cannot be modified and is grayed out.

Additionally, the “DNS Current Configuration” section of the

option ROM utility has the following read-only parameters related

to the DDNS feature:

• Servers from DHCP or Static Servers • Domain Name from DHCP or Static Domain Name • Servers (IP addresses of DNS server 1 and DNS server 2) • Domain (current DNS domain name)

An efficient solution for network administration of RACsUsing a DNS name instead of an IP address can help make system

administration organized and efficient. The DRAC 4 default DNS

name is based on the server’s service tag, which is unique and

easily associated with the server being managed. The DRAC 4

supports dynamic updating of the DNS database with this unique

name-to-address mapping.

Phil Webster is a development engineer in the Dell Remote Management Group. He has a B.S. in Mathematics from Oral Roberts University, an M.A. in Mathematics from the University of South Florida, and an M.S. in Computer Science from Southern Methodist University.

Brian (Limin) Zhang is a software engineer advisor in the Dell Remote Management Group. He has a B.S. from Tsinghua University in China and an M.S. in Electrical Engineering from The University of Texas at Dallas.

Figure 3. DNS configuration settings accessed through the DRAC 4 option ROM utility