Ka\u017ed\u00e1 stanica aj ka\u017ed\u00fd router s\u00fa schopn\u00e9 odosla\u0165 datagram na \u013eubovo\u013en\u00fa cie\u013eov\u00fa adresu na internete. Keby si v\u0161etky stanice aj routre mali uchov\u00e1va\u0165 smer odoslania pre ka\u017ed\u00fa mo\u017en\u00fa stanicu zvl\u00e1\u0161\u0165, potrebovali by sme zhruba 4 miliardy z\u00e1znamov. Samozrejme, \u017ee uchov\u00e1vanie tak\u00fdch ve\u013ek\u00fdch tabuliek nie je vyhovuj\u00face. Namiesto toho sa vyu\u017e\u00edvaj\u00fa kombin\u00e1cie IP adries a masiek tak, aby sa po\u010det z\u00e1znamov smerovacej tabu\u013eky \u010do najviac zredukoval.<\/p>\n
Vezmime si pr\u00edklad smerovacej tabu\u013eky na routri s 5 rozhraniami.<\/p>\n V\u0161imnite si, \u017ee riadky tabu\u013eky s\u00fa usporiadan\u00e9 pod\u013ea po\u010dtu jednotiek v maske zostupne. Predstavme si teraz, \u017ee na tento router pr\u00edde datagram s cie\u013eovou adresou 200.23.25.8. Do ktor\u00e9ho rozhrania sa m\u00e1 tento datagram odosla\u0165? Algoritmus v\u00fdberu postupuje tak, \u017ee vypo\u010d\u00edtava logick\u00fd AND cie\u013eovej adresy datagramu a masky v pr\u00edslu\u0161nom riadku smerovacej tabu\u013eky (takto sa po\u010d\u00edta adresa siete). Ak v\u00fdsledok je zhodn\u00fd s hodnotou v st\u013apci cie\u013e, pravidlo je \u00faspe\u0161n\u00e9 a datagram sa po\u0161le do toho rozhrania, ktor\u00e9 uv\u00e1dza pr\u00edslu\u0161n\u00fd riadok smerovacej tabu\u013eky. Pravidl\u00e1 sa vyhodnocuj\u00fa zhora nadol.<\/p>\n Vysk\u00fa\u0161ajme si teda v\u00fdpo\u010det tohto algoritmu pre cie\u013eov\u00fa adresu 200.23.25.8. Najprv vypo\u010d\u00edtame AND s maskou v prvom riadku. V\u00fdsledok 200.23.25.0 je r\u00f4zny od 200.23.24.0 tak\u017ee pravidlo je ne\u00faspe\u0161n\u00e9. Potom sa vytvor\u00ed AND adresy 200.23.25.8 s maskou 255.255.248.0. V\u00fdsledok 200.23.24.0 je zhodn\u00fd s cie\u013eom v tre\u0165om riadku, pravidlo je \u00faspe\u0161n\u00e9 a datagram je zaslan\u00fd cez rozhranie 2.<\/p>\n Tret\u00ed a \u0161tvrt\u00fd riadok tabu\u013eky sa l\u00ed\u0161ia iba v metrike. V takomto pr\u00edpade je mo\u017en\u00e9 posiela\u0165 tento datagram aj cez rozhranie 5, aj cez rozhranie 2 (obe cesty s\u00fa spr\u00e1vne), ale preferovan\u00e9 je rozhranie s ni\u017e\u0161\u00edm \u010d\u00edslom metriky.<\/p>\n V\u0161imnime si, \u017ee posledn\u00fd riadok smerovacej tabu\u013eky m\u00e1 masku 0.0.0.0, s ktorou ke\u010f urob\u00edme logick\u00fd AND, v\u00fdsledok bude v\u017edy 0.0.0.0. Z toho vypl\u00fdva, \u017ee ak sa testuje aj posledn\u00e9 pravidlo, je \u00faspe\u0161n\u00e9 v\u017edy.<\/p>\n E\u0161te sme nespom\u00ednali, na\u010do je st\u013apec br\u00e1na. Inform\u00e1cie o br\u00e1ne s\u00fa potrebn\u00e9 pre spojov\u00fa vrstvu (spomenieme nesk\u00f4r, ke\u010f ju budeme prebera\u0165). Ak je v st\u013apci br\u00e1na uveden\u00e9 0.0.0.0, znamen\u00e1 to, \u017ee dan\u00e9 rozhranie je v rovnakej sieti ako stanica s cie\u013eovou adresou z datagramu. Napr\u00edklad vieme, \u017ee stanica s IP adresou 200.23.25.8 sa nach\u00e1dza v rovnakej sieti ako rozhranie routra s \u010d\u00edslom 2 a aj rozhranie routra s \u010d\u00edslom 5. Samozrejme aj IP adresy t\u00fdchto rozhran\u00ed routra s\u00fa potom z rovnakej siete. Napr\u00edklad by to mohli by\u0165 IP adresa 200.23.25.1 a 200.23.25.254.<\/p>\n Ak je v st\u013apci br\u00e1na uveden\u00e1 nejak\u00e1 konkr\u00e9tna IP adresa, v na\u0161om pr\u00edklade 200.23.1.1, ide o adresu najbli\u017e\u0161ieho routra, cez ktor\u00fd p\u00f4jde datagram na svojej ceste k cie\u013eovej stanici. Ak ide o posledn\u00fd riadok s cie\u013eom aj maskou 0.0.0.0, hovor\u00edme o\u00a0default routri<\/strong>, teda routri, cez ktor\u00fd sa sp\u00e1jame s na\u0161im providerom a ktor\u00fd n\u00e1s prip\u00e1ja do internetu.<\/p>\n","protected":false},"excerpt":{"rendered":" Ka\u017ed\u00e1 stanica aj ka\u017ed\u00fd router s\u00fa schopn\u00e9 odosla\u0165 datagram na \u013eubovo\u013en\u00fa cie\u013eov\u00fa adresu na internete. Keby si v\u0161etky stanice aj routre mali uchov\u00e1va\u0165 smer odoslania…<\/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\/325"}],"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=325"}],"version-history":[{"count":1,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/325\/revisions"}],"predecessor-version":[{"id":326,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/325\/revisions\/326"}],"wp:attachment":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/media?parent=325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/categories?post=325"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/tags?post=325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n\n
\n cie\u013e<\/td>\n maska<\/td>\n br\u00e1na<\/td>\n rozhranie<\/td>\n metrika<\/td>\n<\/tr>\n \n 200.23.24.0<\/td>\n 255.255.255.0<\/td>\n 0.0.0.0<\/td>\n 1<\/td>\n 0<\/td>\n<\/tr>\n \n 200.23.16.0<\/td>\n 255.255.248.0<\/td>\n 0.0.0.0<\/td>\n 3<\/td>\n 0<\/td>\n<\/tr>\n \n 200.23.24.0<\/td>\n 255.255.248.0<\/td>\n 0.0.0.0<\/td>\n 2<\/td>\n 0<\/td>\n<\/tr>\n \n 200.23.24.0<\/td>\n 255.255.248.0<\/td>\n 0.0.0.0<\/td>\n 5<\/td>\n 10<\/td>\n<\/tr>\n \n 0.0.0.0<\/td>\n 0.0.0.0<\/td>\n 200.23.1.1<\/td>\n 4<\/td>\n 0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n