{"id":633,"date":"2017-10-06T01:53:34","date_gmt":"2017-10-06T01:53:34","guid":{"rendered":"http:\/\/wiki.thomasandsofia.com\/?p=633"},"modified":"2017-10-15T20:37:58","modified_gmt":"2017-10-15T20:37:58","slug":"dns-101","status":"publish","type":"post","link":"https:\/\/wiki.thomasandsofia.com\/?p=633","title":{"rendered":"DNS 101 (54)"},"content":{"rendered":"<p><a href=\"https:\/\/www.udemy.com\/aws-certified-solutions-architect-associate\/learn\/v4\/t\/lecture\/2050692?start=0\" target=\"_blank\" rel=\"noopener\">https:\/\/www.udemy.com\/aws-certified-solutions-architect-associate\/learn\/v4\/t\/lecture\/2050692?start=0<\/a><\/p>\n<p>IPv4=32 bits (4,294,967,296 addresses)<\/p>\n<p>IPv6=128 bits (340,282,366,920,938,463,463,374,607,431,768,211,456 (340 undecillion addresses)<\/p>\n<p>Top Level Domains<\/p>\n<ul>\n<li>.com<\/li>\n<li>.edu<\/li>\n<li>.org<\/li>\n<\/ul>\n<p>Second Level Domain (Optional)<\/p>\n<ul>\n<li>.co.uk<\/li>\n<li>.gov.uk<\/li>\n<li>.com.au<\/li>\n<\/ul>\n<p>Top level domain names are controlled by Internet Assigned Numbers Authority (IANA) in a root zone database which is a database of all available top level domains.\u00a0 You can view this database by visiting: <a href=\"http:\/\/www.iana.org\/domains\/root\/db\" target=\"_blank\" rel=\"noopener\">http:\/\/www.iana.org\/domains\/root\/db<\/a><\/p>\n<p>A Registrar is an authority that can assign domain names directly under one or more top-level domains.\u00a0 These domains are registered with InterNIC, a service of ICANN, which enforces uniqueness of doamind names across the Internet.\u00a0 Each domain name becomes registered in a central database known as the WhoIS database<\/p>\n<p>Popular Registrars<\/p>\n<ul>\n<li>Godaddy.com<\/li>\n<li>123-reg.co.uk<\/li>\n<\/ul>\n<p>SOA=Start Of Authority<\/p>\n<ul>\n<li>Name of server that supplied the data for the zone<\/li>\n<li>Administrator (email address?)<\/li>\n<li>Current version of the data file<\/li>\n<li># of seconds a secondary Name Server should wait before checking for updates<\/li>\n<li># of seconds a secondary Name Server should wait before retrying a failed zone transfer<\/li>\n<li>Maximum # of seconds that a secondary Name Server can use data before it must either be refreshed or expire.<\/li>\n<li>Default # of seconds for the TTL file on resource records<\/li>\n<\/ul>\n<p>NS=Name Server<\/p>\n<ul>\n<li>Name Server records are used by Top Level Domain servers to direct traffic to the Content DNS server which contains the authoritative DNS records.<\/li>\n<\/ul>\n<p>A=Address<\/p>\n<ul>\n<li>Directs a domain name to an IP Address<\/li>\n<li>example.com IN A 123.45.67.89<\/li>\n<\/ul>\n<p>TTL= Time To Live<\/p>\n<ul>\n<li>The length of time (in seconds) a DNS record may be cached on either the Resolving Server or the User&#8217;s own local PC.\u00a0 The lower the TTL, the faster changes to records can propagate throughout the Internet.<\/li>\n<\/ul>\n<p>CNAME=Canonical Name<\/p>\n<ul>\n<li>Used to resolve one domain name to another.<\/li>\n<li>www.example.com IN CNAME example.com.<\/li>\n<\/ul>\n<p>Alias<\/p>\n<ul>\n<li>Work like CNAME records assigning domain names to the IP of another domain.<\/li>\n<li>Difference: CNAME cannot be used with a root domain (zone apex record)\n<ul>\n<li>You cannot set: example.com IN CNAME elb1234.elb.amazonaws.com.<\/li>\n<li>example.com must have either an A record or an Alias record.<\/li>\n<\/ul>\n<\/li>\n<li>Proprietary to Route 53\n<ul>\n<li>Route 53 automatically recognizes changes to Amazon resources (such as an Elastic Load Balancer&#8217;s Public IP and automatically reflects those changes in DNS answers for the domain with any additional changes to the hosted zone that contains the Alias record.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Exam Tips<\/p>\n<ul>\n<li>ELBs do not have pre-defined IPv4 addresses.\u00a0 You must resolve to them using a DNS name.<\/li>\n<li>Understand the differences between an Alias Record and CNAME\n<ul>\n<li>Given the choice, always choose an Alias Record over a CNAME<\/li>\n<\/ul>\n<\/li>\n<li><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>https:\/\/www.udemy.com\/aws-certified-solutions-architect-associate\/learn\/v4\/t\/lecture\/2050692?start=0 IPv4=32 bits (4,294,967,296 addresses) IPv6=128 bits (340,282,366,920,938,463,463,374,607,431,768,211,456 (340 undecillion addresses) Top Level Domains .com .edu .org Second Level Domain (Optional) .co.uk .gov.uk .com.au Top level domain names are controlled by Internet Assigned Numbers Authority (IANA) in a root zone database which is a database of all available top level domains.\u00a0 You can view this ..<\/p>\n<div class=\"clear-fix\"><\/div>\n<p><a href=\"https:\/\/wiki.thomasandsofia.com\/?p=633\" title=\"read more...\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18,19],"tags":[],"class_list":["post-633","post","type-post","status-publish","format-standard","hentry","category-amazon-web-services-aws","category-route53"],"_links":{"self":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/633","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=633"}],"version-history":[{"count":4,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/633\/revisions"}],"predecessor-version":[{"id":638,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=\/wp\/v2\/posts\/633\/revisions\/638"}],"wp:attachment":[{"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=633"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=633"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wiki.thomasandsofia.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=633"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}