1. Copyright © 2007 by Scott Orr and the Trustees of Indiana University
DNS and DHCP
CSCI N321 – System and Network Administration
Copyright © 2007 by Scott Orr and the Trustees of Indiana University

2. Section Overview
DNS Overview
Bind
DNS Record Types
DHCP

3. References Internet Software Consortium RedHat Deployment Guide
Chapter 17 – DNS
Chapter 21 – DHCP

4. In the beginning… Early name resolution /etc/hosts
All addresses in shared file
Never 100% accurate
/etc/hosts
IP_Addr Hostname [Aliases…]
localhost.localdomain localhost
pegasus.cs.iupui.edu pegasus

5. Domain Name Service (DNS)
Allows for IP-Hostname translations
Distributed Hierarchical Database
Hostname to IP address
IP Address to Hostname
Root Servers (A-M)
Mail Server addressing
Resolver Library calls
Protocol to exchange data

6. DNS Management
Internet Corporation for Assigned Names and Numbers (ICANN)
Registries
ARIN – North America
RIPE - Europe
APNIC – Asian Pacific
AfriNIC - Africa
LACNIC – Latin America
Domain Registrars and ISPs
Authoritative DNS Servers

7. Whois Queries Owner Location Domain name Domain DNS Servers
IP Address Block
Contact Information
Administrative (Tech)
Abuse
Noc

8. ISC BIND Primary DNS Server Software in use
Started as a graduate student project
Versions
4.x – Depreciated
8.x – Maintenance Development only
9.x – Active Development
Authoritative (master & slave)
Caching
Recursive/Non-recursive

9. /etc/named.conf (Config)
options {
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
// query-source address * port 53; };
controls {
inet allow { localhost; } keys { rndckey; };

10. /etc/named.conf (Zones)
zone "." IN {
type hint;
file "named.ca"; };
zone "localdomain" IN {
type master;
file "localdomain.zone";
allow-update { none; };
zone "localhost" IN {
file "localhost.zone";
zone " in-addr.arpa" IN {
type master;
file "named.local";
allow-update { none; }; };
// CS Domain Config
zone "cs.iupui.edu" {
file "dns.cs.iupui.edu";
zone " in-addr.arpa" {
file "rev ";
include "/etc/rndc.key";

11. Zone Files Typically in /var/named/ Forward and reverse files
Record Format
[name] [ttl] [class] type data
TTL – Time to keep data cached
Class
IN (Internet)
CN (ChaosNet – No longer used)
HS (Hesoid – internal database)

12. SOA Records Server Name Contact Name
Serial (Must be increased w/ change)
Refresh Secondary
Retry Refresh
Expire non-refreshed entries
Minimum time to live

13. SOA Record Example
@ IN SOA klingon.cs.iupui.edu. root.klingon.cs.iupui.edu. (
; Serial - increase when file changes
; Refresh secondaries every 2 hours
; Retry refresh every 20 minutes
; Expire non-refreshed entries after 30 days
7200 ) ; Minimum time-to-live is 2 hours

14. Name Server Records Which name servers support this domain
Does not differentiate between master and slave servers
Example:
IN NS klingon.cs.iupui.edu.
IN NS dns1.iu.edu.
IN NS dns2.iu.edu.

15. Address (A) Records A Records – Maps hostnames to IP addresses Format
Hostname IN A #.#.#.#
Examples:
tempest IN A
pegasus IN A
enigma IN A

16. Pointer (PTR) Records PTR Records – Maps IP addresses to hostnames
Format
# IN PTR FQDN.
Examples:
IN PTR tempest.cs.iupui.edu.
IN PTR pegasus.cs.iupui.edu.
IN PTR enigma.cs.iupui.edu.

17. Conical Name (CNAME) Records
Aliases for hostnames
Usually associated with Services
Format
Alias IN CNAME Hostname
Examples:
imap IN CNAME tempest
ns IN CNAME klingon
smtp IN CNAME tempest
www IN CNAME enigma
webmail IN CNAME tempest

18. Mail Exchanger (MX) Records
Special records for domain servers
Prioritization and round robin capability
Format
Domain IN MX pri host
Examples:
cs.iupui.edu. IN MX tempest
cs.iupui.edu. IN MX enigma

19. Other Record Types Service (SVC) Text (TXT) HINFO
Associated with network Services
Text (TXT)
Notes (also SPF information)
HINFO
Host information (no longer used)

20. ISC DHCPd Provides IP addresses to client systems
Static – Based on MAC Address
Dynamic – Given to unknown hosts
Optionally provides other Network settings
Subnet Masks
DNS Servers ( /etc.resolv.conf )
Default Gateway
Network and Broadcast Addresses
Lease times

21. /etc/dhcpd.conf authorative; #ddns-update-style ad-hoc;
ddns-update-style none;
one-lease-per-client true;
host camera {
hardware ethernet 00:40:8c:5b:c1:91;
fixed-address ; }
# Block Bad MAC address
host ronin {
hardware ethernet 00:20:e0:67:53:68;
subnet netmask {
option domain-name "cs.iupui.edu";
option domain-name-servers
option subnet-mask ;
option broadcast-address ;
option routers ;
pool {
range ;
default-lease-time 7200;
max-lease-time ;
deny known clients; }

22. /etc/dhcpd.leases Active Lease Entry Expired Lease Entry
starts /12/05 04:14:12;
ends /12/05 06:14:12;
binding state active;
next binding state free;
hardware ethernet 00:13:72:da:2c:ad;
uid "\001\000\023r\332,\255";
client-hostname "in-csci-16sl247"; }
Expired Lease Entry
lease {
starts /12/04 22:45:28;
ends /12/05 00:45:28;
tstp /12/05 00:45:28;
binding state free;
hardware ethernet 00:18:8b:d9:d5:a9;
uid "\001\000\030\213\331\325\251";
client-hostname "in-csci-lt1"; }