00000004.htm

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referrals&nbsp;to&nbsp;other&nbsp;name&nbsp;servers.&nbsp;&nbsp;The&nbsp;domain&nbsp;system&nbsp;also&nbsp;defines&nbsp;<BR>
procedures&nbsp;for&nbsp;caching&nbsp;retrieved&nbsp;data&nbsp;and&nbsp;for&nbsp;periodic&nbsp;refreshing&nbsp;of&nbsp;<BR>
data&nbsp;defined&nbsp;by&nbsp;the&nbsp;system&nbsp;administrator.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;system&nbsp;administrators&nbsp;provide:&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;The&nbsp;definition&nbsp;of&nbsp;zone&nbsp;boundaries.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Master&nbsp;files&nbsp;of&nbsp;data.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Updates&nbsp;to&nbsp;master&nbsp;files.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Statements&nbsp;of&nbsp;the&nbsp;refresh&nbsp;policies&nbsp;desired.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;domain&nbsp;system&nbsp;provides:&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Standard&nbsp;formats&nbsp;for&nbsp;resource&nbsp;data.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Standard&nbsp;methods&nbsp;for&nbsp;querying&nbsp;the&nbsp;database.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;Standard&nbsp;methods&nbsp;for&nbsp;name&nbsp;servers&nbsp;to&nbsp;refresh&nbsp;local&nbsp;data&nbsp;from&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;foreign&nbsp;name&nbsp;servers.&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Mockapetris&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[Page&nbsp;5]&nbsp;<BR>
&nbsp;<BR>
RFC&nbsp;1034&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Domain&nbsp;Concepts&nbsp;and&nbsp;Facilities&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;November&nbsp;1987&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
2.4.&nbsp;Elements&nbsp;of&nbsp;the&nbsp;DNS&nbsp;<BR>
&nbsp;<BR>
The&nbsp;DNS&nbsp;has&nbsp;three&nbsp;major&nbsp;components:&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;The&nbsp;DOMAIN&nbsp;NAME&nbsp;SPACE&nbsp;and&nbsp;RESOURCE&nbsp;RECORDS,&nbsp;which&nbsp;are&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;specifications&nbsp;for&nbsp;a&nbsp;tree&nbsp;structured&nbsp;name&nbsp;space&nbsp;and&nbsp;data&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;associated&nbsp;with&nbsp;the&nbsp;names.&nbsp;&nbsp;Conceptually,&nbsp;each&nbsp;node&nbsp;and&nbsp;leaf&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;of&nbsp;the&nbsp;domain&nbsp;name&nbsp;space&nbsp;tree&nbsp;names&nbsp;a&nbsp;set&nbsp;of&nbsp;information,&nbsp;and&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;query&nbsp;operations&nbsp;are&nbsp;attempts&nbsp;to&nbsp;extract&nbsp;specific&nbsp;types&nbsp;of&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;information&nbsp;from&nbsp;a&nbsp;particular&nbsp;set.&nbsp;&nbsp;A&nbsp;query&nbsp;names&nbsp;the&nbsp;domain&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;name&nbsp;of&nbsp;interest&nbsp;and&nbsp;describes&nbsp;the&nbsp;type&nbsp;of&nbsp;resource&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;information&nbsp;that&nbsp;is&nbsp;desired.&nbsp;&nbsp;For&nbsp;example,&nbsp;the&nbsp;Internet&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;uses&nbsp;some&nbsp;of&nbsp;its&nbsp;domain&nbsp;names&nbsp;to&nbsp;identify&nbsp;hosts;&nbsp;queries&nbsp;for&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;address&nbsp;resources&nbsp;return&nbsp;Internet&nbsp;host&nbsp;addresses.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;NAME&nbsp;SERVERS&nbsp;are&nbsp;server&nbsp;programs&nbsp;which&nbsp;hold&nbsp;information&nbsp;about&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;the&nbsp;domain&nbsp;tree's&nbsp;structure&nbsp;and&nbsp;set&nbsp;information.&nbsp;&nbsp;A&nbsp;name&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;server&nbsp;may&nbsp;cache&nbsp;structure&nbsp;or&nbsp;set&nbsp;information&nbsp;about&nbsp;any&nbsp;part&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;of&nbsp;the&nbsp;domain&nbsp;tree,&nbsp;but&nbsp;in&nbsp;general&nbsp;a&nbsp;particular&nbsp;name&nbsp;server&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;has&nbsp;complete&nbsp;information&nbsp;about&nbsp;a&nbsp;subset&nbsp;of&nbsp;the&nbsp;domain&nbsp;space,&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;and&nbsp;pointers&nbsp;to&nbsp;other&nbsp;name&nbsp;servers&nbsp;that&nbsp;can&nbsp;be&nbsp;used&nbsp;to&nbsp;lead&nbsp;to&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;information&nbsp;from&nbsp;any&nbsp;part&nbsp;of&nbsp;the&nbsp;domain&nbsp;tree.&nbsp;&nbsp;Name&nbsp;servers&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;know&nbsp;the&nbsp;parts&nbsp;of&nbsp;the&nbsp;domain&nbsp;tree&nbsp;for&nbsp;which&nbsp;they&nbsp;have&nbsp;complete&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;information;&nbsp;a&nbsp;name&nbsp;server&nbsp;is&nbsp;said&nbsp;to&nbsp;be&nbsp;an&nbsp;AUTHORITY&nbsp;for&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;these&nbsp;parts&nbsp;of&nbsp;the&nbsp;name&nbsp;space.&nbsp;&nbsp;Authoritative&nbsp;information&nbsp;is&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;organized&nbsp;into&nbsp;units&nbsp;called&nbsp;ZONEs,&nbsp;and&nbsp;these&nbsp;zones&nbsp;can&nbsp;be&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;automatically&nbsp;distributed&nbsp;to&nbsp;the&nbsp;name&nbsp;servers&nbsp;which&nbsp;provide&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;redundant&nbsp;service&nbsp;for&nbsp;the&nbsp;data&nbsp;in&nbsp;a&nbsp;zone.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;RESOLVERS&nbsp;are&nbsp;programs&nbsp;that&nbsp;extract&nbsp;information&nbsp;from&nbsp;name&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;servers&nbsp;in&nbsp;response&nbsp;to&nbsp;client&nbsp;requests.&nbsp;&nbsp;Resolvers&nbsp;must&nbsp;be&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;able&nbsp;to&nbsp;access&nbsp;at&nbsp;least&nbsp;one&nbsp;name&nbsp;server&nbsp;and&nbsp;use&nbsp;that&nbsp;name&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;server's&nbsp;information&nbsp;to&nbsp;answer&nbsp;a&nbsp;query&nbsp;directly,&nbsp;or&nbsp;pursue&nbsp;the&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;query&nbsp;using&nbsp;referrals&nbsp;to&nbsp;other&nbsp;name&nbsp;servers.&nbsp;&nbsp;A&nbsp;resolver&nbsp;will&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;typically&nbsp;be&nbsp;a&nbsp;system&nbsp;routine&nbsp;that&nbsp;is&nbsp;directly&nbsp;accessible&nbsp;to&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;user&nbsp;programs;&nbsp;hence&nbsp;no&nbsp;protocol&nbsp;is&nbsp;necessary&nbsp;between&nbsp;the&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;resolver&nbsp;and&nbsp;the&nbsp;user&nbsp;program.&nbsp;<BR>
&nbsp;<BR>
These&nbsp;three&nbsp;components&nbsp;roughly&nbsp;correspond&nbsp;to&nbsp;the&nbsp;three&nbsp;layers&nbsp;or&nbsp;views&nbsp;<BR>
of&nbsp;the&nbsp;domain&nbsp;system:&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;From&nbsp;the&nbsp;user's&nbsp;point&nbsp;of&nbsp;view,&nbsp;the&nbsp;domain&nbsp;system&nbsp;is&nbsp;accessed&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;through&nbsp;a&nbsp;simple&nbsp;procedure&nbsp;or&nbsp;OS&nbsp;call&nbsp;to&nbsp;a&nbsp;local&nbsp;resolver.&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The&nbsp;domain&nbsp;space&nbsp;consists&nbsp;of&nbsp;a&nbsp;single&nbsp;tree&nbsp;and&nbsp;the&nbsp;user&nbsp;can&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;request&nbsp;information&nbsp;from&nbsp;any&nbsp;section&nbsp;of&nbsp;the&nbsp;tree.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;From&nbsp;the&nbsp;resolver's&nbsp;point&nbsp;of&nbsp;view,&nbsp;the&nbsp;domain&nbsp;system&nbsp;is&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;composed&nbsp;of&nbsp;an&nbsp;unknown&nbsp;number&nbsp;of&nbsp;name&nbsp;servers.&nbsp;&nbsp;Each&nbsp;name&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
Mockapetris&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[Page&nbsp;6]&nbsp;<BR>
&nbsp;<BR>
RFC&nbsp;1034&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Domain&nbsp;Concepts&nbsp;and&nbsp;Facilities&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;November&nbsp;1987&nbsp;<BR>
&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;server&nbsp;has&nbsp;one&nbsp;or&nbsp;more&nbsp;pieces&nbsp;of&nbsp;the&nbsp;whole&nbsp;domain&nbsp;tree's&nbsp;data,&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;but&nbsp;the&nbsp;resolver&nbsp;views&nbsp;each&nbsp;of&nbsp;these&nbsp;databases&nbsp;as&nbsp;essentially&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;static.&nbsp;<BR>
&nbsp;<BR>
&nbsp;&nbsp;&nbsp;-&nbsp;From&nbsp;a&nbsp;name&nbsp;server's&nbsp;point&nbsp;of&nbsp;view,&nbsp;the&nbsp;domain&nbsp;system&nbsp;consists&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;of&nbsp;separate&nbsp;sets&nbsp;of&nbsp;local&nbsp;information&nbsp;called&nbsp;zones.&nbsp;&nbsp;The&nbsp;name&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;server&nbsp;has&nbsp;local&nbsp;copies&nbsp;of&nbsp;some&nbsp;of&nbsp;the&nbsp;zones.&nbsp;&nbsp;The&nbsp;name&nbsp;server&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;must&nbsp;periodically&nbsp;refresh&nbsp;its&nbsp;zones&nbsp;from&nbsp;master&nbsp;copies&nbsp;in&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;local&nbsp;files&nbsp;or&nbsp;foreign&nbsp;name&nbsp;servers.&nbsp;&nbsp;The&nbsp;name&nbsp;server&nbsp;must&nbsp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;concurrently&nbsp;process&nbsp;queries&nbsp;that&nbsp;arrive&nbsp;from&nbsp;resolvers.&nbsp;<BR>
&nbsp;<BR>
In&nbsp;the&nbsp;interests&nbsp;of&nbsp;performance,&nbsp;implementations&nbsp;may&nbsp;couple&nbsp;these&nbsp;<BR>
functions.&nbsp;&nbsp;For&nbsp;example,&nbsp;a&nbsp;resolver&nbsp;on&nbsp;the&nbsp;same&nbsp;machine&nbsp;as&nbsp;a&nbsp;name&nbsp;server&nbsp;<BR>
might&nbsp;share&nbsp;a&nbsp;database&nbsp;consisting&nbsp;of&nbsp;the&nbsp;the&nbsp;zones&nbsp;managed&nbsp;by&nbsp;the&nbsp;name&nbsp;<BR>
server&nbsp;and&nbsp;the&nbsp;cache&nbsp;managed&nbsp;by&nbsp;the&nbsp;resolver.&nbsp;<BR>
&nbsp;<BR>
3.&nbsp;DOMAIN&nbsp;NAME&nbsp;SPACE&nbsp;and&nbsp;RESOURCE&nbsp;RECORDS&nbsp;<BR>
&nbsp;<BR>
3.1.&nbsp;Name&nbsp;space&nbsp;specifications&nbsp;and&nbsp;terminology&nbsp;<BR>
&nbsp;<BR>
The&nbsp;domain&nbsp;name&nbsp;space&nbsp;is&nbsp;a&nbsp;tree&nbsp;structure.&nbsp;&nbsp;Each&nbsp;node&nbsp;and&nbsp;leaf&nbsp;on&nbsp;the&nbsp;<BR>
tree&nbsp;corresponds&nbsp;to&nbsp;a&nbsp;resource&nbsp;set&nbsp;(which&nbsp;may&nbsp;be&nbsp;empty).&nbsp;&nbsp;The&nbsp;domain&nbsp;<BR>
system&nbsp;makes&nbsp;no&nbsp;distinctions&nbsp;between&nbsp;the&nbsp;uses&nbsp;of&nbsp;the&nbsp;interior&nbsp;nodes&nbsp;and&nbsp;<BR>
leaves,&nbsp;and&nbsp;this&nbsp;memo&nbsp;uses&nbsp;the&nbsp;term&nbsp;&quot;node&quot;&nbsp;to&nbsp;refer&nbsp;to&nbsp;both.&nbsp;<BR>
&nbsp;<BR>
Each&nbsp;node&nbsp;has&nbsp;a&nbsp;label,&nbsp;which&nbsp;is&nbsp;zero&nbsp;to&nbsp;63&nbsp;octets&nbsp;in&nbsp;length.&nbsp;&nbsp;Brother&nbsp;<BR>
nodes&nbsp;may&nbsp;not&nbsp;have&nbsp;the&nbsp;same&nbsp;label,&nbsp;although&nbsp;the&nbsp;same&nbsp;label&nbsp;can&nbsp;be&nbsp;used&nbsp;<BR>
for&nbsp;nodes&nbsp;which&nbsp;are&nbsp;not&nbsp;brothers.&nbsp;&nbsp;One&nbsp;label&nbsp;is&nbsp;reserved,&nbsp;and&nbsp;that&nbsp;is&nbsp;<BR>
the&nbsp;null&nbsp;(i.e.,&nbsp;zero&nbsp;length)&nbsp;label&nbsp;used&nbsp;for&nbsp;the&nbsp;root.&nbsp;<BR>
&nbsp;<BR>
The&nbsp;domain&nbsp;name&nbsp;of&nbsp;a&nbsp;node&nbsp;is&nbsp;the&nbsp;list&nbsp;of&nbsp;the&nbsp;labels&nbsp;on&nbsp;the&nbsp;path&nbsp;from&nbsp;the&nbsp;<BR>
node&nbsp;to&nbsp;the&nbsp;root&nbsp;of&nbsp;the&nbsp;tree.&nbsp;&nbsp;By&nbsp;convention,&nbsp;the&nbsp;labels&nbsp;that&nbsp;compose&nbsp;a&nbsp;<BR>
domain&nbsp;name&nbsp;are&nbsp;printed&nbsp;or&nbsp;read&nbsp;left&nbsp;to&nbsp;right,&nbsp;from&nbsp;the&nbsp;most&nbsp;specific&nbsp;<BR>
(lowest,&nbsp;farthest&nbsp;from&nbsp;the&nbsp;root)&nbsp;to&nbsp;the&nbsp;least&nbsp;specific&nbsp;(highest,&nbsp;closest&nbsp;<BR>
to&nbsp;the&nbsp;root).&nbsp;<BR>
&nbsp;<BR>
Internally,&nbsp;programs&nbsp;that&nbsp;manipulate&nbsp;domain&nbsp;names&nbsp;should&nbsp;represent&nbsp;them&nbsp;<BR>
as&nbsp;sequences&nbsp;of&nbsp;labels,&nbsp;where&nbsp;each&nbsp;label&nbsp;is&nbsp;a&nbsp;length&nbsp;octet&nbsp;followed&nbsp;by&nbsp;<BR>
an&nbsp;octet&nbsp;string.&nbsp;&nbsp;Because&nbsp;all&nbsp;domain&nbsp;names&nbsp;end&nbsp;at&nbsp;the&nbsp;root,&nbsp;which&nbsp;has&nbsp;a&nbsp;<BR>
null&nbsp;string&nbsp;for&nbsp;a&nbsp;label,&nbsp;these&nbsp;internal&nbsp;representations&nbsp;can&nbsp;use&nbsp;a&nbsp;length&nbsp;<BR>
byte&nbsp;of&nbsp;zero&nbsp;to&nbsp;terminate&nbsp;a&nbsp;domain&nbsp;name.&nbsp;<BR>