IP and DNS - kimschles/schlesinger-knowledge GitHub Wiki

IP Addresses

Khan Academy: IP and DNS

• Internet Protocol Address
• A number to identify a piece of hardware on a network (the internet and others)
• IP addresses were developed by Vint Cerf and Bob Kahn to make sure that networks could communicate with one another.
• Most common IPv4 format: 151.101.65.121
  • Each number is represented in bits.
  • IPv4 addresses contain 32 bits
  • 8 bits for each part of the address
  • The first slot is for country/network
  • The second slot is for region/network
  • The third slot is for a subnetwork
  • The fourth slot is the addresses of the specific device
• IPv6 format: 2400:cb00:2048:1::c629:d7a2 (hexidecimal)
  • 128 bits per addresses

Private IP Addresses

• Used behind a router or NAT device
• Sometimes called 'local IP addresses'
• The addresses are not available publically
• Private Addresses Ranges:
  • 10.0.0.0 to 10.255.255.255
  • 172.16.0.0 to 172.31.255.255
  • 192.168.0.0 to 192.168.255.255
• Said another way:
  • 10.0.0.0/8 (~ 16 million addresses)
  • 172.16.0.0/12 (~ 1 million)
  • 192.168.0.0/16 (~ 65,000)
• Most home routers have the address 192.168.1.1
• Find your default gateway (on MacOS): netstat -rn | grep default
• Reserved IP addresses
  • 127.0.0.1 to 127.255.255.255
  • Loopback address (localhost!)

• DNS servers have a list of domain names and the IP address of those domains

• IP versions: IPv4 and IPv6

• Kinds of IP addresses:

  • Private
  • Public
  • Static
  • Dynamic

• DNS servers are divided by zones.

• Cloudflare: DNS

• OSU DevOps Bootcamp: DNS

• Checks cache

• If chache doesn't have a domain name and IP address saved, the browser (?) checks the root server

• The root server will tell the computer to check the top-level domain node (.org, .com, .io)

• Recursive

• Authoritative

• DNS servers cache records. Each record has a Time to Live (TTL) that specifies how long to cache the record.

• Wildcard DNS record: a record in a DNS zone that matches requests for domains that don't exist. *.example.com

Check DNS

• host <domain.com>
• netstat -rn
  • See the IP tables on your computer
• dig NS <domain.com>

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Software Freedom School, January 5, 2019

https://cfedde.gitlab.io/how-dns-works-and-why-you-care/

The Domain Name System is a distributed Hierarchical database with low referential integrity.

• low referential integrity means that different servers might have different information

DNS is organized as a hierarchy. There is a tree that contains records. The top is root, then TLDs, then second-level domains

Root name server

• The first step in resolving human readable domain names into their IP address
• .

TLD = top level domain

• .com, .edu, .gov, etc.
• You can lookup the root name servers for a TLD with dig <tld> ns, for example dig com ns

• A records (for ipv4)
• AAAA records (for ipv6)
• PTR records
• MX records (mail servers)
• SRV
• LOC
• TXT (text)

Fun fact: DNS uses UDP, not TCP

• whois <domain.name>

  • a domain name directory maintained by ICANN and IANA
  • whois gives your information about the domain name registrar and who administers the domain

• dig: domain information groper (perform DNS lookups)

• A way to get information from a DNS name server

  • dig kimschlesinger.com
    • Returns the A records
  • dig NS <domain_here>
  • When no command line arguments or options are given, dig will perform an NS query for "." (the root).
  • dig your_domain_name.com +short for the IP addresses

Digital Ocean dig

• nslookup is like dig, but returns less information

• /etc/resolv.conf on linux machines
• See DNS configuration on a mac: scutil --dns

• Describe the purpose of DNS
• Explain the difference between TCP and UDP
• View information about a specific domain name with whois
• View the A records of a specific domain name with dig
• Describe the difference between NS and SOA
• Identify the root name servers for the info domain using dig
• Illustrate how DNS resolves a domain name