• How Resolutions Work
• [Non-]Authoritative Data
• Domains/Zones
• Types of Name Servers

• What is asked?
• Who is asked?
• How is it asked?

• Address (ping.G-Squared.COM)
• Name (192.168.254.1)
• Mail Exchanger (G-Squared.COM)
• Start of Authority

• Initial Name Server
• Root Name Server(s)
• Delegated Name Servers

• Recursive Query
  • Ask Server to chase everything down and return
• Iterative Query
• Ask Server for "best guess"
  • ping.G-Squared.COM root returns server for COM
  • COM server returns server for G-Squared.COM
  • G-Squared.COM server returns info

• Cached Data answers are non-authoritative
• Primary/Secondary answers authoritative
• All answers are then cached for some time

• Domain is hierarchical collection of information (G-Squared.COM)
• Zone is specific sub-set of data (lab.G-Squared.COM)
• IN-AddR.ARPA is Domain, 127.in-addr.arpa is Zone

• Primary Master
• Secondary Master
• Caching Only
• Slave

• Distribute administrative control over sub-set of larger domain to other organizations
• Answer iterative queries about delegated sub-domain with pointers to servers
• Need "glue" record with address!
• Avoid LAME Delegation!!

• Start of Authority Record (SOA)
• Name to Address Mapping (A records)
• Address to Name Mapping (PTR records)
• Name Aliasing (CNAME records)
• Mail Exchanging (MX)
• Host Information [cpu/os] (HINFO)
• Well Known Services (WKS)

• Specifies which machine generated zone information.
• Specifies who to contact if errors
• Specifies Version/Serial number for secondary servers
• Specifies refresh, retry, expire, and default time to live for entries in zone

• Name to Address
  • Given a name returns an address
• Address to Name
  • Given an address (in special format) returns name
• Name Aliasing
  • Given a name, returns the true name and address

• Specifies which servers "know" about the domain to accept mail for it
• Weighting is included
  • Lower numbers have HIGHER priority
• Not all must "deliver" mail locally, but must know how to get to final site

• HINFO specifies hardware CPU and software O/S version
• WKS specifies which types of services are provided by the system in which type of protocol
  • TCP ( smtp named telnet. )
  • UDP ( named nfs. )

• Sendmail 8.x (at least 8.6.10)
• Checks CNAME records, canonicalizes
• Checks "ANY" records, to get MX, and A (precedence to MX)

• named.boot
• resolv.conf
• Zone DB files

• Directory specification
  • directory /var/namedb
• Root-Level Server "cache"
  • cache . root.cache
• Primary for 127 network
  • primary 127.in-addr.arpa arpa/127
• Primary/Secondary/Extras.

• Domain Specification
  • domain domain.name
• Name Server Directives
  • nameserver ip.addr.no.names
  • nameserver other-ip.addr.no.names
• Domain Search Directives
  • search domain.name other.domain.name.

• Start of Authority Directive
• Name Server Specifications
• Other Resource Records (A, MX, HINFO)

@ IN SOA machine.domain. hostmaster.domain. (
       1996101001 ; YYYYMMddVV serial number
       10800      ; secondary refresh 3 hrs
       3600       ; sec. retry after failure 1 hr
       604800     ; expire time 1 wk
       86400      ; default TTL for entries )

@ IN SOA pang.G-Squared.com. dns.G-Squared.COM. (
      1996101001 10800 3600 604800 86400 )

[domain] [TTL]  IN  NS   F.Q.D.N.

  IN NS  ping.G-Squared.COM.

• Address Records

   ping     IN   A     192.168.254.1
   pang     IN   A     192.168.254.2
  

• CNAME (Alias) Records

   mailhost IN   CNAME ping
  

• MX (Mail Exchanger) Records

• Specify NS records for "." domain
• Have a very long TTL value
  
• . 999999 IN NS ns.nic.ddn.mil.
• ns.nic.ddn.mil 999999 IN A 192.x.x.x

• Restrict who can do Zone Transfers
  • xfernets in named.boot
• Working around firewall implementations
  • Inside and outside DNS servers