The Domain Name System

1
The Domain Name System

• Unix System Administration

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2
DNS History Mystery

• During the time of the dinosaurs (ARPANET)
• Single host file managed centrally and
  distributed to all hosts on the ARPANET
• Consumed lots o bandwidth
• DNS Is Born
• Original Unix work done by grad students at
  Berkeley, later managed by the ISC
• Hierarchical, distributed database
• Each site responsible for their portion of DNS

3
Whats In a Named?

• DNS
• Domain Name System
• BIND
• Berkeley Internet Name Domain system
• named or in.named
• Name of the BIND executable

4
Defining DNS Definitively

• Hierarchical namespace for hosts and IP addresses
• Host table implemented as a distributed database
• Resolver or library routines for querying the
  database
• Improved routing of email
• Mechanism for finding services on the net
• Protocol for exchanging naming info

5
DNS Goes Both Ways

• Resolves names to IP addresses
• Also resolves IP address to names (reverse DNS)

6
Vixies Various Versions

• Paul Vixie was the major maintainer for BIND
  version 8
• Version 4 is still in use, but should be
  considered obsolete
• Version 8 provides many advances that improved
  efficiency, security and robustness
• Version 9 is a total rewrite and supports
  threads, multiprocessors IPv6 and more
• There was no version 5, 6 or 7

7
What Kind of Bindage Are You Into?

• Bind 4 used a config file called /etc/named.boot
• Bind 8, 9 use /etc/named.conf
• To determine if version 8 or 9 use
• dig _at_server version.bind txt chaos
• e.g. dig _at_beast version.bind txt chaos

8
Masters, Slaves and the Authorities

• Authoritative Servers
• Master server (keeps official copy of zone info
  on disk)
• Slave server (gets copy of zone info from master
  via zone transfer)
• Cache Servers
• Never authoritative
• Load root domain servers but all others are
  accumulated in memory only

9
Binding Your Clients

• Bind Client Resolver Configuration
• /etc/resolv.conf
• domain or search directives
• nameserver directives (at most 3)
• /etc/nsswitch.conf on some systems (like Solaris
  and Linux)

10
Putting Your Server In a Bind

• /etc/named.conf
• Zone files
• See page 438 for record types

11
/etc/named.conf
options directory "/var/dns"
pid-file "/etc/named.pid" fake-iquery
yes logging category lame-servers
null category cname null
zone "." in type hint
file "named.cache" zone "0.0.127.in-addr.arpa"
in type master file
"named.local"
12
/etc/named.conf (continued)
zone "91.159.in-addr.arpa" in type
master file "tcnj.hosts.reversed" zon
e "TCNJ.EDU" in type master
file "tcnj.hosts" zone "Trenton.EDU" in
type master file "trenton.hosts"
13
_at_ IN SOA
beast.TCNJ.EDU. admin.beast.TCNJ.EDU. (
5923 serial number
10800 Refresh 3 hours
3600 Retry 1 hour
604800 Expire 168 hours/1 week
43200 ) Minimum 12 hour
IN NS
beast.TCNJ.EDU. IN
NS seuss.TCNJ.EDU.
IN NS snuffy.TCNJ.EDU. loc
alhost 43200 IN A
127.0.0.1 beast IN A
159.91.15.220 beast IN MX 20
beast.TCNJ.EDU. TCNJ.EDU. IN MX 20
beast.TCNJ.EDU. lion IN A
159.91.15.221 lion IN MX 20
beast.TCNJ.EDU. tsclion IN CNAME
lion.TCNJ.EDU. sa.tcnj.edu. IN
NS cartman.sa.tcnj.edu. cartman.sa.tcnj.edu.
IN A 159.91.8.228
14
91.159.in-addr.arpa. IN SOA beast.TCNJ.EDU.
ssivy.beast.TCNJ.EDU. (
5774 serial number
10800 Refresh 3 hours
3600 Retry 1 hour
604800 Expire 168 hours/1 week
43200 ) Minimum 12 hour
IN NS
beast.Trenton.EDU. IN
NS snuffy.Trenton.EDU.
IN NS
seuss.Trenton.EDU. localhost 43200 IN
A 127.0.0.1 220.15.91.159.IN-ADDR.
ARPA. PTR beast.TCNJ.EDU. 221.15.91.159.IN-ADD
R.ARPA. PTR lion.TCNJ.EDU. 228.8.91.159.IN-AD
DR.ARPA. cartman.sa.tcnj.edu.
15
_at_ IN SOA beast.trenton.edu.
admin.beast.tcnj.edu. ( 3
Serial number 10800 Refresh
rate in seconds for secondary servers
3600 Retry in seconds after failure
3600000 Expire in seconds
86400) Default time-to-live in seconds
IN NS beast.tcnj.edu. 1 IN
PTR localhost.
16
Root Name Servers
. 3600000 IN NS
A.ROOT-SERVERS.NET. A.ROOT-SERVERS.NET.
3600000 A 198.41.0.4 .
3600000 NS B.ROOT-SERVERS.NET. B.ROOT
-SERVERS.NET. 3600000 A
128.9.0.107 . 3600000
NS C.ROOT-SERVERS.NET. C.ROOT-SERVERS.NET.
3600000 A 192.33.4.12 .
3600000 NS D.ROOT-SERVERS.NET. D.RO
OT-SERVERS.NET. 3600000 A
128.8.10.90 . 3600000
NS E.ROOT-SERVERS.NET. E.ROOT-SERVERS.NET.
3600000 A 192.203.230.10 .
3600000 NS F.ROOT-SERVERS.NET. F
.ROOT-SERVERS.NET. 3600000 A
192.5.5.241 lt blah, blah, blah gt .
3600000 NS M.ROOT-SERVERS.NET. M
.ROOT-SERVERS.NET. 3600000 A
202.12.27.33