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

Section Overview DNS Overview Bind DNS Record Types DHCP

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

In the beginning… Early name resolution /etc/hosts All addresses in shared file Never 100% accurate /etc/hosts IP_Addr Hostname [Aliases…] 127.0.0.1 localhost.localdomain localhost 134.68.140.203 pegasus.cs.iupui.edu pegasus

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

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

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

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

/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 127.0.0.1 allow { localhost; } keys { rndckey; };

/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 "0.0.127.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 "140.68.134.in-addr.arpa" { file "rev.134.68.140"; include "/etc/rndc.key";

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)

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

SOA Record Example @ IN SOA klingon.cs.iupui.edu. root.klingon.cs.iupui.edu. ( 2007112500 ; Serial - increase when file changes 7200 ; Refresh secondaries every 2 hours 1200 ; Retry refresh every 20 minutes 2592000 ; Expire non-refreshed entries after 30 days 7200 ) ; Minimum time-to-live is 2 hours

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.

Address (A) Records A Records – Maps hostnames to IP addresses Format Hostname IN A #.#.#.# Examples: tempest IN A 134.68.140.202 pegasus IN A 134.68.140.203 enigma IN A 134.68.140.206

Pointer (PTR) Records PTR Records – Maps IP addresses to hostnames Format # IN PTR FQDN. Examples: 202 IN PTR tempest.cs.iupui.edu. 203 IN PTR pegasus.cs.iupui.edu. 206 IN PTR enigma.cs.iupui.edu.

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

Mail Exchanger (MX) Records Special records for domain email servers Prioritization and round robin capability Format Domain. IN MX pri host Examples: cs.iupui.edu. IN MX 10 tempest cs.iupui.edu. IN MX 100 enigma

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

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

/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 10.234.140.21; } # Block Bad MAC address host ronin { hardware ethernet 00:20:e0:67:53:68; subnet 134.68.140.0 netmask 255.255.255.0 { option domain-name "cs.iupui.edu"; option domain-name-servers 134.68.140.1 option subnet-mask 255.255.255.0; option broadcast-address 134.68.140.255; option routers 134.68.140.100; pool { range 134.68.140.101 134.68.140.199; default-lease-time 7200; max-lease-time 144000; deny known clients; }

/etc/dhcpd.leases Active Lease Entry Expired Lease Entry starts 3 2007/12/05 04:14:12; ends 3 2007/12/05 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 134.68.140.121 { starts 2 2007/12/04 22:45:28; ends 3 2007/12/05 00:45:28; tstp 3 2007/12/05 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"; }