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Shadow Cipher

Networking Services

Introduction to Network Services

Why do we need DNS?

  • IP Address(32 bit binary number) - 10.10.1.1

  • MAC Address(48 bit binary number) 00 0a 95 9d 68 16

  • Domain Name System (DNS) A global and highly distributed network services that resolved strings of letters into IP addresses for you

  • Domain Name The term we use for something that can be resolved by DNS

The many steps of Name resolution

  • IP Address

  • Subnet Mask

  • Gateway for a host

  • DNS server

  • There are five primary types of DNS servers:

  1. Caching name servers
  2. Recursive name servers
  3. Root name servers
  4. TLD name servers
  5. Authoratative name servers

  • Caching and recursive name servers Purpose is to store known domain name lookups for a certain amount of time

  • Recursive name servers Performs full DNS resolution requests

  • Time to live(TTL) A value, in seconds that can be configured by the owner of a domain name for how long a name server is allowed to cache an entry before it should discard it and perform a full resolution again

  • user - caching/recursive name server - 13 root servers

  • Anycast A technique that’s used to route traffic to different destinations depending on factors like location, congestion, or link health

DNS and UDP

  • UDP isconnectionless

Resource Record types

  • A record Used to point a certain domain name at a certain IPv4 IP address

  • DNS round robin

  • www.microsoft.com

  • 10.1.1.1

  • 10.1.1.2

  • 10.1.1.3

  • 10.1.1.4

  • Quad A record (AAAA) very similar to an A record, except that it returns an IPv6 address instead of an IPv4 address

  • CNAME record used to redirect traffic from one domain to another

  • microsoft.com

  • Cannonical Name

  • By setting up a CNAME that points microsoft.com at www.microsoft.com, you’d only have to change the A record for www.microsoft.com

  • Mail exchange (MX) This resource record is used in order to deliver email to the correct server

  • Service record(SRV) Used to define the location of various specific services

  • Text record(TXT) Originally intended to be used only for associating some descriptive text with a domain name for human consumption

Anatomy of a Domain Name

  • Top level dommain(TLD) The last part of a domain name

  • the internet Corporation for Assigned Names and Numbers

  • Domains Used to demarcate where control moves from a TLd name server to an authorative name server

  • Fully qualified domain name(FQDN) When you combine all of these parts together, you have what’s known as this

  • host.sub.sub.subdomain.domain.com

  • DNS can techniqually support up to 127 levels of domain in total for a single fully qualified domain name

DNS zones

Allow for easier control over multiple levels of a domain

  • Zone files Simple configuration files that declare all resource record for a particular zone

  • Start of Authority (SOA) Declare the zone and the name of the name server thaat is authorative for it

  • NS records indicates other name servers that might also be responsible for this zone

  • reverse lookup zone files These let DNS resolvers ask for an IP and get the FQDN assocaited with it returned

  • Pointer resource record (PTR) Resolved as IP to a name