{"id":327,"date":"2020-04-06T00:13:22","date_gmt":"2020-04-05T22:13:22","guid":{"rendered":"http:\/\/tech.sosthe.sk\/?p=327"},"modified":"2020-04-06T16:32:29","modified_gmt":"2020-04-06T14:32:29","slug":"4-5-dhcp-dynamic-host-configuration-protocol","status":"publish","type":"post","link":"http:\/\/tech.sosthe.sk\/index.php\/2020\/04\/06\/4-5-dhcp-dynamic-host-configuration-protocol\/","title":{"rendered":"4.5.\u2002DHCP: Dynamic Host Configuration Protocol"},"content":{"rendered":"

DHCP protokol je pop\u00edsan\u00fd v\u00a0RFC 2131.<\/a><\/p>\n

IP adresa, maska, default router aj lok\u00e1lne rekurz\u00edvne DNS servery sa daj\u00fa nastavi\u0165 manu\u00e1lne cez pr\u00edslu\u0161n\u00e9 konfigura\u010dn\u00e9 nastavenia v opera\u010dnom syst\u00e9me. DHCP v\u0161ak pon\u00faka mo\u017enos\u0165 nastavi\u0165 si v\u0161etky tieto hodnoty dynamicky, bez nutnosti manu\u00e1lneho nastavovania.<\/p>\n

DHCP je aplika\u010dn\u00fd protokol vyu\u017e\u00edvaj\u00faci UDP protokol. Typick\u00fd scen\u00e1r, kedy sa pou\u017eije DHCP protokol je pri pripojen\u00ed zariadenia do siete. Toto zariadenie netu\u0161\u00ed ni\u010d o tom, ak\u00e1 je sie\u0165ov\u00e1 adresa tejto siete, ktor\u00fa IP adresu si m\u00e1 nastavi\u0165, ak\u00e1 je d\u013a\u017eka masky a podobne. T\u00fdm p\u00e1dom netu\u0161\u00ed ani to, na ktorom po\u010d\u00edta\u010di je spusten\u00fd DHCP server, na ktor\u00fd sa m\u00e1 napoji\u0165 a pop\u00fdta\u0165 si od neho potrebn\u00e9 \u00fadaje. Jedin\u00e9, \u010do vie, je, \u017ee ak je DHCP server v danej sieti, tak po\u010d\u00fava na porte 67. Vy\u0161le cez UDP protokol teda DHCP spr\u00e1vu, naz\u00fdvan\u00fa\u00a0DHCP discover<\/strong>,\u00a0pre v\u0161etky po\u010d\u00edta\u010de v danej sieti<\/em>, t. j. nastav\u00ed ako cie\u013eov\u00fa adresu broadcastov\u00fa adresu lok\u00e1lnej siete 255.255.255.255 a ako adresu zdroja nastav\u00ed 0.0.0.0, teda stanicu lok\u00e1lnej siete. Ke\u010f\u017ee cie\u013eov\u00e1 adresa je broadcastov\u00e1, t\u00fato spr\u00e1vu musia prija\u0165 v\u0161etky zariadenia. T\u00e1to spr\u00e1va okrem in\u00e9ho obsahuje aj n\u00e1hodne vygenerovan\u00fd identifik\u00e1tor.<\/p>\n

Ak je v sieti DHCP server, reaguje na t\u00fato spr\u00e1vu spr\u00e1vou, naz\u00fdvanou\u00a0DHCP offer<\/strong>, pon\u00fakaj\u00facou nov\u00fa IP adresu. Ke\u010f\u017ee po\u010d\u00edta\u010d, ktor\u00e9mu je t\u00e1to spr\u00e1va ur\u010den\u00e1 nem\u00e1 e\u0161te IP adresu, aj DHCP server zvol\u00ed ako cie\u013eov\u00fa IP adresu 255.255.255.255. T\u00e1to spr\u00e1va okrem pon\u00faknutej IP adresy obsahuje ten ist\u00fd identifik\u00e1tor, ako bol v spr\u00e1ve DHCP discover, \u010falej IP adresu DHCP servera, pon\u00fakan\u00fa \u017eivotnos\u0165 IP adresy, default router a default DNS servery. N\u00e1\u0161 \u017eiadaj\u00faci po\u010d\u00edta\u010d m\u00f4\u017ee tak\u00fdch spr\u00e1v dosta\u0165 aj viac, ak je v sieti viac DHCP serverov. Jednu z nich si vyberie.<\/p>\n

Teraz u\u017e n\u00e1\u0161 \u017eiadaj\u00faci po\u010d\u00edta\u010d vie, ak\u00fa adresu m\u00f4\u017ee dosta\u0165. Vygeneruje spr\u00e1vu\u00a0DHCP request<\/strong>, ktor\u00e1 po\u017eaduje pridelenie tejto IP adresy. Aj t\u00e1to spr\u00e1va m\u00e1 za cie\u013eov\u00fa adresu 255.255.255.255, a v tele m\u00e1 v\u0161etky parametre, ktor\u00e9 sa vyskytovali v DHCP offer spr\u00e1ve.<\/p>\n

DHCP server teraz odpovie potvrdzovacou spr\u00e1vou\u00a0DHCP ACK<\/strong>, op\u00e4\u0165 so v\u0161etk\u00fdmi parametrami. Aj t\u00e1to spr\u00e1va ide pre cie\u013eov\u00fa adresu 255.255.255.255. V tejto chv\u00edli si n\u00e1\u0161 \u017eiadaj\u00faci po\u010d\u00edta\u010d m\u00f4\u017ee nastavi\u0165 pon\u00fakan\u00fa IP adresu a za\u010da\u0165 komunikova\u0165 s in\u00fdmi po\u010d\u00edta\u010dmi v sieti alebo cez default router aj s ostatn\u00fdmi sie\u0165ami.<\/p>\n

Ke\u010f\u017ee ka\u017ed\u00e1 IP adresa pridelen\u00e1 DHCP serverom m\u00e1 svoju \u017eivotnos\u0165, m\u00f4\u017ee sa sta\u0165, \u017ee po\u010d\u00edta\u010du u\u017e pomaly kon\u010d\u00ed p\u00f4\u017ei\u010dka IP adresy (DHCP lease) a m\u00f4\u017ee si po\u017eiada\u0165 o pred\u013a\u017eenie platnosti. Na tak\u00fato po\u017eiadavku u\u017e sta\u010dia iba posledn\u00e9 dve spr\u00e1vy z p\u00f4vodnej \u0161tvorspr\u00e1vovej komunik\u00e1cie, preto\u017ee po\u010d\u00edta\u010d u\u017e vie, v akej je sieti a vie aj to, \u017ee o ak\u00fa IP adresu \u017eiada. Takto sa d\u00e1 dosiahnu\u0165, \u017ee po\u010d\u00edta\u010d s dynamicky nastavenou IP adresou m\u00f4\u017ee by\u0165 pripojen\u00fd ve\u013emi dlho a st\u00e1le (bez prest\u00e1vky) ma\u0165 pridelen\u00fa svoju IP adresu. T\u00e1to komunik\u00e1cia u\u017e m\u00f4\u017ee prebieha\u0165 unicastom, teda ako cie\u013eov\u00e9 adresy m\u00f4\u017eu by\u0165 pou\u017eit\u00e9 priamo adresy DHCP servera resp. \u017eiadaj\u00facej stanice.<\/p>\n

Protokol DHCP je roz\u0161\u00edren\u00edm p\u00f4vodn\u00e9ho protokolu BOOTP (RFC 951<\/a>,RFC 1542<\/a>), ktor\u00fd bol p\u00f4vodne ur\u010den\u00fd na pomoc pri bootovan\u00ed po\u010d\u00edta\u010dov po sieti. Vtedy mus\u00ed poveda\u0165 bootovan\u00e9mu po\u010d\u00edta\u010du, kde sa nach\u00e1dza bootovac\u00ed s\u00fabor. Typicky tento bootovac\u00ed s\u00fabor je ulo\u017een\u00fd na FTP serveri.<\/p>\n

DHCP \u0161pecifik\u00e1cia umo\u017e\u0148uje aj to, aby nemusel by\u0165 v ka\u017edej sieti samostatn\u00fd DHCP server, ale aby sta\u010dil jeden DHCP server na pokrytie viacer\u00fdch siet\u00ed. Na to sl\u00fa\u017ei takzvan\u00fd relay agent, ktor\u00fd je obvykle s\u00fa\u010das\u0165ou routrov ako doplnkov\u00e1 slu\u017eba. Relay agent preposiela DHCP po\u017eiadavky do siete, kde sa nach\u00e1dza DHCP server a tie\u017e DHCP odpovede do siete \u017eiadaj\u00faceho po\u010d\u00edta\u010da.<\/p>\n

DHCP je ve\u013emi ob\u013e\u00faben\u00fd protokol najm\u00e4 v s\u00favislosti s masov\u00fdm roz\u0161\u00edren\u00edm notebookov, ktor\u00e9 sa be\u017ene prip\u00e1jaj\u00fa do r\u00f4znych siet\u00ed (doma, v \u0161kole, v pr\u00e1ci, v kaviarni, na stanici, \u2026) a v\u0161ade si nastavia IP adresu dynamicky, bez potreby ru\u010dn\u00e9ho nastavovania. \u010eal\u0161ou v\u00fdhodou je to, \u017ee sa d\u00e1 vyrie\u0161i\u0165 aj stav, \u017ee je rozsah pridelen\u00fdch IP adries men\u0161\u00ed ako po\u010det po\u010d\u00edta\u010dov, ktor\u00e9 sa v danej sieti zvykn\u00fa vyskytova\u0165 (nie v\u0161etky naraz). Potom sa niektor\u00e9 IP adresy daj\u00fa pou\u017ei\u0165 raz pre jeden, raz pre in\u00fd po\u010d\u00edta\u010d.<\/p>\n","protected":false},"excerpt":{"rendered":"

DHCP protokol je pop\u00edsan\u00fd v\u00a0RFC 2131. IP adresa, maska, default router aj lok\u00e1lne rekurz\u00edvne DNS servery sa daj\u00fa nastavi\u0165 manu\u00e1lne cez pr\u00edslu\u0161n\u00e9 konfigura\u010dn\u00e9 nastavenia v…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"_links":{"self":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/327"}],"collection":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/comments?post=327"}],"version-history":[{"count":1,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/327\/revisions"}],"predecessor-version":[{"id":328,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/327\/revisions\/328"}],"wp:attachment":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/media?parent=327"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/categories?post=327"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/tags?post=327"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}