DNS 101 - What it is and how it works

DNS 101:What it is, how it works

What is it?

DNS = Domain Name SystemOne large distributed database: The DNS

Client/Server system with:Name Servers - contain information about some segments of the database

Resolvers - create queries and send them across the network to a name server

A Brief History ofDNS and BIND

Late 60’s: US DoD Advanced Research Projects Agency creates ARPAnet

Updates sent to SRI-NIC; HOSTS.TXT published twice a week.

Early 80’s: TCP/IP added to BSD, and ARPAnet growth explodes

1984, Paul Mockapetris releases RFCs 882 and 883 (later superseded by 1034 and 1035); JEEVES released

1985, Berkeley releases first version of BIND, written by Kevin Dunlap

1993, BIND 4.9 is released by DEC, managed by Paul Vixie, assisted by others; 1994, BIND 4.9.2 is released by Vixie Enterprises; 1995, BIND 4.9.3 released by ISC

The DNS Tree StructureThe Distributed Database

Who Manages What?Delegation of Authority

How does it work?Anatomy of a DNS Lookup

•Your PC Asks:

•Q: Where is www.cira.ca?


•Office-mail asks:


•A: I don’t know, but I can tell you who knows about .ca.•ca01.cira.ca




•A: I don’t know, but I can tell you who knows about .ca.•ca01.cira.ca•192.228.21.9




•A: I don’t know, but I can tell you who knows about cira.ca.•ns01.cira.ca•192.228.22.70




•A: It’s at 192.228.23.21


•A: www.cira.ca is at 192.228.23.21


•Your PC Asks:

•Q: Where is www.microsoft.ca?




•A: I don’t know, but I can tell you who knows about .ca.•ca01.cira.ca•192.228.21.9




•A: I don’t know, but I can tell you who knows about microsoft.ca.•ns4.msft.net



•Q: Where is ns4.msft.net?

•A: I don’t know, but I can tell you who knows about .net.•a.gtld-servers.net



•Q: Where is ns4.msft.net?

•A: I don’t know, but I can tell you who knows about msft.net.•ns4.msft.net•207.46.66.75




•A: www.microsoft.ca is an alias for microsoft.ca. microsoft.ca has two IP addresses: 207.46.130.108 and 207.46.250.119.


www.smallbusiness.ca hosted by hostingco.ca

hostingco.ca puts their customer domains on separate name servers from their own domain


•Q: Where is www.smallbusiness.ca?

•A: I don’t know, but I can tell you who knows about smallbusiness.ca.•ns3.hostingco.ca


•Q: Where is ns3.hostingco.ca?

•A: I don’t know, but I can tell you who knows about hostingco.ca•ns1.hostingco.ca•192.0.2.10


•Q: Where is ns3.hostingco.ca?

•A: ns3.hostingco.ca is at 192.0.2.8


•Q: Where is www.smallbusiness.ca?

•A: It’s at 192.0.2.81.

What if Something Breaks?Data Replication and Authority

What if Something Breaks?Dot-ca Data Replication

What Can The Data Say?Record Types

Address Records (A) -- www.cira.ca is at 192.228.23.21

Pointer Records (PTR) -- 192.228.23.21 is the address for www.cira.ca

Name Server Records (NS) -- ns01.cira.ca is a nameserver for cira.ca

Mail Exchanger Records (MX) -- mail.cira.ca handles mail for cira.ca

Canonical Name (CNAME) -- www.cira.ca is an alias for cira.ca (cira.ca is the canonical name of www.cira.ca)

What Does it Look Like?Sample .ca Zone Data

•microsoft.ca. IN NS ns1.msft.net.• IN NS ns2.msft.net.• IN NS ns3.msft.net.• IN NS ns4.msft.net.• IN NS ns5.msft.net.

•webnames.ca. IN NS relay.cdnnet.ca.• IN NS ns1.cs.ubc.ca.• IN NS blackwidow.webnames.ca.

•cira.ca. IN NS ns01.cira.ca.• IN NS ns02.cira.ca.• IN NS ns03.cira.ca.

•relay.cdnnet.ca. IN A 192.73.5.1•blackwidow.webnames.ca. IN A 207.232.123.229

•ns01.cira.ca. IN A 192.228.22.70•ns02.cira.ca. IN A 192.228.22.71•ns03.cira.ca. IN A 192.228.30.8

DNS 101 - What it is and how it works

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Transcript of DNS 101 - What it is and how it works