Domain Name System (DNS) - Revision history

Sebastian at 00:36, 1 February 2025

2025-02-01T00:36:01Z

← Older revision		Revision as of 02:36, 1 February 2025
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	$ host -t txt _dmarc.example.com		$ host -t txt _dmarc.example.com
	_dmarc.example.com descriptive text "v=DMARC1; p=reject; rua=mailto:dmarc@dmarc.example.com; ruf=mailto:dmarc@dmarc.example.com; rf=afrf; pct=100;"		_dmarc.example.com descriptive text "v=DMARC1; p=reject; rua=mailto:dmarc@dmarc.example.com; ruf=mailto:dmarc@dmarc.example.com; rf=afrf; pct=100;"
			</pre>

			===BIMI records===
			''Main article: [[Brand Indicators for Message Identification (BIMI)]]''

			Example:
			<pre>
			$ host -t txt default._bimi.example.com
			default._bimi.example.com descriptive text "v=BIMI1; l=https://example.com/logo.svg; a=https://example.com/image/certificate.pem;"
	</pre>		</pre>

Sebastian at 14:25, 3 September 2023

2023-09-03T14:25:38Z

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	* In "example.com", the TLD is "com" and "example" is the SLD/PSD.		* In "example.com", the TLD is "com" and "example" is the SLD/PSD.

	The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels. However, if I create a separate zone for "sub.example.com" ~~(see also [[#Domain delegation]])~~, then "sub.example.com" is a responsible domain on top of it's own hierarchy.		The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels. However, if I create a separate zone for "sub.example.com", then "sub.example.com" is a responsible domain on top of it's own hierarchy (see also [[#Domain delegation]]).

	=Record types=		=Record types=

Sebastian at 14:24, 3 September 2023

2023-09-03T14:24:59Z

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	DNS is a hierarchical system. On top of the hierarchy-stryucture of a domain name is the '''[[wikipedia:DNS_root_zone\|toplevel domain (TLD)]]'''. Examples of toplevel domains are "[[wikipedia:.com\|com]]", "[[wikipedia:.net\|net]]", "[[wikipedia:.org\|org]]", "[[wikipedia:.nl\|nl]]", "[[wikipedia:.berlin\|berlin]]" and many more. TLDs are provided by [[wikipedia:Internet_Assigned_Numbers_Authority\|IANA]].		DNS is a hierarchical system. On top of the hierarchy-stryucture of a domain name is the '''[[wikipedia:DNS_root_zone\|toplevel domain (TLD)]]'''. Examples of toplevel domains are "[[wikipedia:.com\|com]]", "[[wikipedia:.net\|net]]", "[[wikipedia:.org\|org]]", "[[wikipedia:.nl\|nl]]", "[[wikipedia:.berlin\|berlin]]" and many more. TLDs are provided by [[wikipedia:Internet_Assigned_Numbers_Authority\|IANA]].

	In the example "example.com", "com" is the toplevel domain and "example" is the '''second level domain (SLD)''' or '''public suffix domain (PSD)'''.		In the example "example.com", "com" is the toplevel domain and "example" is the '''second level domain (SLD)''' or '''public suffix domain (PSD)'''. The PSD is also called "'''organisational domain'''".

	~~Some~~ toplevel domains have a second-level domain included in their hierarchy. One famous example is "[[wikipedia:.uk#Second-level_domains\|co.uk]]"~~. In "example.co.uk", "[[wikipedia:.uk\|uk]]" is the TLD, "co" is the SLD and "example" is the PSD~~.		SLD and PSD are not exactly the same thing, because some toplevel domains have a second-level domain included in their hierarchy. One famous example is "[[wikipedia:.uk#Second-level_domains\|co.uk]]".

	The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels.		* In "example.co.uk", "[[wikipedia:.uk\|uk]]" is the TLD, "co" is the SLD and "example" is the PSD.
			* In "example.com", the TLD is "com" and "example" is the SLD/PSD.

			The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels. However, if I create a separate zone for "sub.example.com" (see also [[#Domain delegation]]), then "sub.example.com" is a responsible domain on top of it's own hierarchy.

	=Record types=		=Record types=

Sebastian at 02:37, 3 September 2023

2023-09-03T02:37:57Z

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	<pre>		<pre>
	$ host ~~-t a~~ aliasdomain.example.net		$ host aliasdomain.example.net
	aliasdomain.example.net is an alias for example.com.		aliasdomain.example.net is an alias for example.com.
	example.com has address 192.168.10.34		example.com has address 192.168.10.34

Sebastian at 02:36, 3 September 2023

2023-09-03T02:36:55Z

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	\|-		\|-
	! scope="row"\| TXT		! scope="row"\| TXT
	\|\| Holds a piece of text \|\| <pre>$ host -t txt ~~_spf.~~example.com		\|\| Holds a piece of text \|\| <pre>$ host -t txt example.com
	~~_spf.~~example.com descriptive text "~~v=spf1 ip4:192.168.10.34 ip6:fe80::1ff:fe23:4567:890a ~all~~"</pre>		example.com descriptive text "lorem ipsum"</pre>
	\|-		\|-
	! scope="row"\| PTR		! scope="row"\| PTR
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	==CNAME Record==		==CNAME Record==

	CNAME records are aliases. Let's stick with the example from the above table and "aliasdomain.example.net" is an alias of "example.com", as you can see from the CNAME record. If we now first query the A-Records and then the ~~TXT record~~ for "aliasdomain.example.net", this will be the output:		CNAME records are aliases. Let's stick with the example from the above table and "aliasdomain.example.net" is an alias of "example.com", as you can see from the CNAME record. If we now first query the A-Records and then the MX records for "aliasdomain.example.net", this will be the output:

	<pre>		<pre>
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	example.com has IPv6 address fe80::1ff:fe23:4567:890a		example.com has IPv6 address fe80::1ff:fe23:4567:890a

	$ host -t ~~txt~~ aliasdomain.example.net		$ host -t mx aliasdomain.example.net
	aliasdomain.example.net is an alias for example.com.		aliasdomain.example.net is an alias for example.com.
	example.com ~~descriptive text "v=spf1 ip4:192~~.~~168~~.10.~~34 ip6:fe80::1ff:fe23:4567:890a ~all"~~		example.com mail is handled by 10 mx2.example.com.
			example.com mail is handled by 5 mx1.example.com.
	</pre>		</pre>

Sebastian at 02:31, 3 September 2023

2023-09-03T02:31:16Z

← Older revision		Revision as of 04:31, 3 September 2023
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			[[Category:Deliverability]]
			[[Category:Authentication]]
	The '''Domain Name System''' is a naming system for the internet. It was originally invented to assign names to IPs, because names are more easy to remember than the numbers in IP addresses. meanwhile, DNS has more purposes than to translate names in numbers only.		The '''Domain Name System''' is a naming system for the internet. It was originally invented to assign names to IPs, because names are more easy to remember than the numbers in IP addresses. meanwhile, DNS has more purposes than to translate names in numbers only.

Sebastian at 02:20, 3 September 2023

2023-09-03T02:20:41Z

← Older revision		Revision as of 04:20, 3 September 2023
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	DNS is a hierarchical system. On top of the hierarchy-stryucture of a domain name is the '''[[wikipedia:DNS_root_zone\|toplevel domain (TLD)]]'''. Examples of toplevel domains are "[[wikipedia:.com\|com]]", "[[wikipedia:.net\|net]]", "[[wikipedia:.org\|org]]", "[[wikipedia:.nl\|nl]]", "[[wikipedia:.berlin\|berlin]]" and many more. TLDs are provided by [[wikipedia:Internet_Assigned_Numbers_Authority\|IANA]].		DNS is a hierarchical system. On top of the hierarchy-stryucture of a domain name is the '''[[wikipedia:DNS_root_zone\|toplevel domain (TLD)]]'''. Examples of toplevel domains are "[[wikipedia:.com\|com]]", "[[wikipedia:.net\|net]]", "[[wikipedia:.org\|org]]", "[[wikipedia:.nl\|nl]]", "[[wikipedia:.berlin\|berlin]]" and many more. TLDs are provided by [[wikipedia:Internet_Assigned_Numbers_Authority\|IANA]].

	In the example "example.com", "com" is the toplevel domain and "example" is the second level domain or public suffix domain (PSD).		In the example "example.com", "com" is the toplevel domain and "example" is the '''second level domain (SLD)''' or '''public suffix domain (PSD)'''.

	Some toplevel domains have a second-level domain ~~(SLD)~~ included in their hierarchy. One famous example is "[[wikipedia:.uk#Second-level_domains\|co.uk]]". In "example.co.uk", "[[wikipedia:.uk\|uk]]" is the TLD, "co" is the SLD and "example" is the PSD.		Some toplevel domains have a second-level domain included in their hierarchy. One famous example is "[[wikipedia:.uk#Second-level_domains\|co.uk]]". In "example.co.uk", "[[wikipedia:.uk\|uk]]" is the TLD, "co" is the SLD and "example" is the PSD.

	The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels.		The '''responsible domain''' is the domain that's on top of a zone. Any responsible domain can have almost infinite subdomains. In our example "sub.example.com", "example.com" is the responsible domain and "sub" is the subdomain. In "sub1.sub2.sub3.example.com", "example.com" is the responsible domain for all subdomain levels.
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	\|-		\|-
	! scope="row"\| NS		! scope="row"\| NS
	\|\| Delegates a ~~(sub)domain~~ to one or more nameservers \|\| <pre>$ host -t ns example.com		\|\| Delegates a subdomain to one or more nameservers \|\| <pre>$ host -t ns example.com
	example.com name server dns2.example.net.		example.com name server dns2.example.net.
	example.com name server dns1.example.net.		example.com name server dns1.example.net.
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	==PTR Record==		==PTR Record==

	~~PTR records, or reverse DNS, are defined in [https://datatracker.ietf.org/doc/html/rfc1035 RFC1035].~~ The reverse lookup is meant to find a name to an IP, instead of the other way around. Because it's not possible to create a DNS zone with an IP, an alias (canonical name) is used for each IP. This alias always has the TLD "arpa", which is reserved for this purpose. IPv4 uses "in-addr.arpa" and IPv6 uses "ip6.arpa".		The reverse lookup is meant to find a name to an IP, instead of the other way around. Because it's not possible to create a DNS zone with an IP, an alias (canonical name) is used for each IP. This alias always has the TLD "arpa", which is reserved for this purpose. IPv4 uses "in-addr.arpa" and IPv6 uses "ip6.arpa".

	Each sending IP should resolve recursively to a domain. This domain is the "hostname". Each hostname should resolve to an IP. This IP should be the same sending IP we started from.		Each sending IP should resolve recursively to a domain. This domain is the "hostname". Each hostname should resolve to an IP. This IP should be the same sending IP we started from.
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	mail-ej1-x632.google.com has IPv6 address 2a00:1450:4864:20::632		mail-ej1-x632.google.com has IPv6 address 2a00:1450:4864:20::632
	</pre>		</pre>

			==NS Record==

			Nameserver records are found on responsible domains. They define which nameserver stores the zone file with resource records for this domain.

	=Domain delegation=		=Domain delegation=

	If you create an NS record for a subdomain, this subdomain now is on top of it's own ~~zone~~. What used to be a subdomain, is now a responsible domain.		If you create an NS record for a subdomain, this subdomain now is responsible for it's own zone, on top of it's own hierarchy. What used to be a subdomain, is now a responsible domain.

	~~For example~~, with DNS delegation it's possible for dns[1\|2].example.com to host the zone for "example.com", while dns[1\|2].example.net ~~hosts~~ the zone for "sub.example.com".		Because of that, with DNS delegation it's possible for - for example - Jake's nameservers (dns[1\|2].example.com) to host the zone for "example.com", while Andrew's nameservers (dns[1\|2].example.net) host the zone for "sub.example.com". While Jake still owns "example.com" and all its subdomains, Andrew is now the only person who can set resource records for the subdomain "sub.example.com", until Jake revokes the delegation by removing the NS records from the subdomain.

	=Useful links=		=Useful links=

	* [[wikipedia:Domain_Name_System]]		* [[wikipedia:Domain_Name_System]]

Sebastian at 01:59, 3 September 2023

2023-09-03T01:59:53Z

← Older revision		Revision as of 03:59, 3 September 2023
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	Example:		Example:
	<pre>host -t ~~aaaa~~ example.com		<pre>
	example.com ~~has IPv6 address~~ fe80::1ff:fe23:4567:890a</pre>		$ host -t txt _spf.example.com
			_spf.example.com descriptive text "v=spf1 ip4:192.168.10.34 ip6:fe80::1ff:fe23:4567:890a ~all"
			</pre>

	===DKIM records===		===DKIM records===

Sebastian at 01:56, 3 September 2023

2023-09-03T01:56:29Z

← Older revision		Revision as of 03:56, 3 September 2023
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	</pre>		</pre>

	=~~DNS~~ delegation=		=Domain delegation=

	If you create an NS record for a subdomain, this subdomain now is on top of it's own zone. What used to be a subdomain, is now a responsible domain.		If you create an NS record for a subdomain, this subdomain now is on top of it's own zone. What used to be a subdomain, is now a responsible domain.

Sebastian at 01:51, 3 September 2023

2023-09-03T01:51:00Z

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