{"id":95716,"date":"2020-10-02T01:42:50","date_gmt":"2020-10-01T23:42:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/inicziativa-dns-flag-day-2020-dlya-resheniya-problem-s-fragmentacziej-i-podderzhkoj-tcp"},"modified":"2020-10-02T01:42:50","modified_gmt":"2020-10-01T23:42:50","slug":"inicziativa-dns-flag-day-2020-dlya-resheniya-problem-s-fragmentacziej-i-podderzhkoj-tcp","status":"publish","type":"post","link":"https:\/\/prohoster.info\/et\/blog\/news\/inicziativa-dns-flag-day-2020-dlya-resheniya-problem-s-fragmentacziej-i-podderzhkoj-tcp","title":{"rendered":"DNS flag day 2020 algatus probleemide lahendamiseks fraktsioonimise ja TCP toe osas.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

T\u00e4nap\u00e4eval korraldavad mitmed suured DNS-teenuste pakkujad ja DNS-serverite tootjad \u00fchis\u00fcrituse DNS lipup\u00e4ev 2020<\/a><\/noindex>, mille eesm\u00e4rk on keskenduda lahendusele<\/a><\/noindex> probleemide<\/a><\/noindex> IP-fragmentatsiooni t\u00f5ttu suurte DNS-s\u00f5numite t\u00f6\u00f6tlemisel. See on juba teine sarnane \u00fcritus, eelmisel aastal «DNS flag day» oli keskendunud<\/a><\/noindex> EDNS-i p\u00e4ringute korrektsele t\u00f6\u00f6tlemisele. <\/p>\n

DNS flag day 2020 algatuse osalised kutsuvad \u00fcles fikseerima EDNS-i soovitatavad puufferi suurused kuni 1232 baitini (MTU suurus 1280 miinus 48 baiti p\u00e4iste jaoks), samuti t\u00f5lkida<\/a><\/noindex> TCP-p\u00e4ringute t\u00f6\u00f6tlemine peab olema serverites kohustuslikult toetatud. RFC 1035 t\u00e4histab kohustuslikult vaid UDP-p\u00e4ringute t\u00f6\u00f6tlemise toetust, samas kui TCP on m\u00e4rgitud soovitatavaks, kuid mitte kohustuslikuks. Uued<\/a><\/noindex> m\u00e4rgitud on ainult UDP p\u00e4ringute t\u00f6\u00f6tlemise toetus, samas kui TCP on m\u00e4rgitud kui soovitav, kuid mitte kohustuslik t\u00f6\u00f6ks. Uued RFC 7766<\/a><\/noindex> ja RFC 5966<\/a><\/noindex> seavad TCP selgelt kohustuslike v\u00f5imaluste hulka, mis on DNS-i korrektseks toimimiseks h\u00e4davajalikud. K\u00e4imasoleva algatuse raames pakutakse v\u00e4lja, et tulla \u00fcle UDP-p\u00e4ringute saatmiselt TCP kasutamisele olukordades, kus EDNS-i puufferi seadistatud suurus ei ole piisav.<\/p>\n

Ettepanekud k\u00f5rvaldab segaduse EDNS-i puhvri suuruse valikul ja lahendavad probleemid suurte UDP-s\u00f5numite fragmenteerimisega, mille t\u00f6\u00f6tlemine toob sageli kaasa pakettide kadumise ja klientide poolseid taimerite \u00fcletamisi. Klientide poolel on EDNS-i puhvri suurus konstantne ning suured vastused saadetakse kohe kliendile TCP kaudu. Suurte s\u00f5numite saatmise v\u00e4listamine UDP-u kaudu lahendab ka probleemid suurte pakettide k\u00f5rvaldamisega m\u00f5nedes tulem\u00fc\u00fcrides ja v\u00f5imaldab blokeerida r\u00fcnnaku<\/a><\/noindex> DNS vahem\u00e4lu rikke korral v\u00f5ivad tekkida probleemid, mis on tingitud fragmentide UDP-pakettide manipuleerimisest (fragmentimisel ei h\u00f5lma teine fragment identifikaatori pead, seet\u00f5ttu saab selle manipuleerida, et ainult kontrollsumma vastaks).<\/p>\n

Alates t\u00e4nasest osalevad DNS-i teenusepakkujad, sealhulgas CloudFlare, Quad 9, Cisco (OpenDNS) ja Google, hakkavad j\u00e4rk-j\u00e4rgult muutma<\/a><\/noindex> EDNS-i puhvri suurust 4096 baitilt 1232 baitini oma DNS-serverites (EDNS-i muudatus kestab 4\u20136 n\u00e4dalat ja aja jooksul h\u00f5lmab see \u00fcha rohkem k\u00fcsimusi). UDP-p\u00e4ringutele, mis ei mahu uude piirangusse, saadetakse vastused TCP kaudu. DNS-serverite tootjad, sealhulgas BIND, Unbound, Knot, NSD ja PowerDNS, avaldavad v\u00e4rskendused, mis muudavad vaikimisi EDNS-i puhvri suuruse 4096 baitilt 1232 baitini. <\/p>\n

L\u00f5ppkokkuv\u00f5ttes v\u00f5ivad rakendatavad muudatused p\u00f5hjustada probleeme DNS-serverite lahendamisel, kui DNS-vastused UDP kaudu \u00fcletavad 1232 bahti ja ei suuda vastust TCP kaudu edastada. Google'i l\u00e4bi viidud katse n\u00e4itas, et EDNS-i puhversuuruse muutmine ei m\u00f5juta t\u00f5rgete taset praktiliselt \u2014 4096 baidi puhversuuruse korral on UDP-k\u00e4rbitud p\u00e4ringute arv 0.345%, TCP kaudu k\u00e4ttesaamatute uuesti vastuste arv on 0.115%. 1232 baidi puhversuuruse korral on need n\u00e4itajad 0.367% ja 0.116%. TCP toetuse muutmine DNS-i kohustuslikuks funktsiooniks toob kaasa probleeme ligikaudu 0.1% DNS-serveritega. T\u00e4heldatakse, et t\u00e4nap\u00e4eva tingimustes ilma TCP-ta on nende serverite t\u00f6\u00f6 juba niikuinii ebastabiilne.<\/p>\n

Autoriteetsete DNS-serverite administraatorid peaksid veenduma, et nende server vastab TCP-le v\u00f5rgupordil 53 ja et antud TCP-port ei ole tulem\u00fc\u00fcriga blokeeritud. Autoriteetne DNS-server ei tohi samuti saata UDP vastuseid, mille suurus \u00fcletab
\nEDNS-i puhvri suurus peab olema seatud serveris 1232 baitiks. Resolveritele kehtivad sarnased n\u00f5uded \u2014 kohustuslik TCP-vastuste v\u00f5imalus, kohustuslik toetus TCP-uuesti k\u00fcsimiseks l\u00fchendatud UDP-vastuse saamisel ja EDNS-i puhvri seadmine 1232 baitiks.<\/p>\n

EDNS-i puhvri suuruse seadistamine erinevates DNS-serverites s\u00f5ltub j\u00e4rgmistest parameetritest:<\/p>\n

  • BIND\n

    options {
    \n edns-udp-size 1232;
    \n max-udp-size 1232;
    \n };<\/p>\n

  • Knot DNS\n

    max-udp-payload: 1232<\/p>\n

  • Knot Resolver\n

    net.bufsize(1232)<\/p>\n

  • PowerDNS Authoritative\n

    udp-truncation-threshold=1232<\/p>\n

  • PowerDNS Recursor\n

    edns-outgoing-bufsize=1232
    \n udp-truncation-threshold=1232<\/p>\n

  • Unbound\n

    edns-buffer-size: 1232<\/p>\n

  • NSD\n

    ipv4-edns-size: 1232
    \n ipv6-edns-size: 1232<\/p>\n

    <\/a><\/noindex><\/p>\n

    Allikas: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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