ot geroy(18-10-2012)

reiting (36)   [ dobre ]  [ zle ]

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Predi da zapochnete da chetete statiiata e dobre da se zapoznaete s purvata chast Kak raboti DNS, chast 1 - Resolvers i Cache survuri.


DNS protokol

Komunikatsiiata na DNS preminava predimno po UDP protokola. Tova garantira vuzmozhno nai-malko zabaviane na otgovorite. Pravilo e che UDP DNS zaiavkite ne triabva da budat po-golemi ot 512 baita, kato se ima vpredvid, che i nai-zle konfiguriranite ruteri shte propuskat UDP paketi s golemina 512 baita. Kogato otgovorut nadvishi tazi golemina, se preminava kum TCP - protokola, a tova e po-bavniiat variant za obmiana na DNS informatsiia.
Vruzkata mezhdu klient i survur se osushtestviava chrez zapitvane (query) i otgovor (answer).
Zapitvaneto se sustoi ot "zapitvane za zapis na resurs" ili Resource Record query (ili za po-kratko RR query) i suotvetno - otgovor s dannite za resursa, ako e otkrit, ili otritsatelen otgovor NXDOMAIN (non-existent domain).

primer

# host -v -t ns google.bg ns1.google.com
Trying "google.bg"
Using domain server:
Name: ns1.google.com
Address: 216.239.32.10#53
Aliases:

;; ->>HEADER ;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 4

;; QUESTION SECTION:
;google.bg. IN NS

;; ANSWER SECTION:
google.bg. 345600 IN NS ns1.google.com.
google.bg. 345600 IN NS ns2.google.com.
google.bg. 345600 IN NS ns4.google.com.
google.bg. 345600 IN NS ns3.google.com.

;; ADDITIONAL SECTION:
ns1.google.com. 345600 IN A 216.239.32.10
ns2.google.com. 345600 IN A 216.239.34.10
ns4.google.com. 345600 IN A 216.239.38.10
ns3.google.com. 345600 IN A 216.239.36.10

Received 173 bytes from 216.239.32.10#53 in 48 ms
V sluchaia pravim zapitvane za RR - tip NS, toest "koi DNS - survuri obsluzhvat zonata google.bg?". Otgovorut kakto se vizhda, sa 4 DNS survura i tehniia TTL (time to live, ili kolko vreme da se "keshirat" zapisite ot DNS cache survurite). Spisukut na tipa zapitvaniia za RR ne e maluk, no po-goliamata chast riadko se polzva. SHTe izbroia nai-chesto izpolzvanite RR queries, pridruzheni s kratko opisanie.

SOA - Start of authority ili "dostoveren iztochnik", ot kudeto sus sigurnost shte razberem koi "master dns" obsluzhva dadeniia domein.
NS - "koi DNS survuri obsluzhvat dadeniia domein?"
A - nai-chesto se izpolzva za svurzvane na hostname kum IP adres. A zapisut www kum domeina linux-bg.org otgovaria na IP adres 212.50.10.155 (www.linux-bg.org).
MX - "koi meil survuri obsluzhvat poshtata za dadeniia domein?"
TXT - mozhe da se izpolzva za vsichko, ako iskate mozhe da si napishete "This is my DNS" i pri RR tip TXT shte poluchite tochno tova. Printsipno se izpolzva za SPF anti-spam zapisi.
CNAME - tova e psevdonim kum drug hostname, naprimer www.google.bg e psevdonim (alias) kum www.l.google.com.
PTR - "na koi hostname otgovaria dadeniia IP adres?", ili tova e obratnoto na A zapis.
AAAA - sushtoto kato A zapis, no za IPv6 adresi.
ANY - vsichki zapisi, kasaeshti dadeniia domein.

Topologiia na DNS

Strukturata na DNS e ierarhichna, kato v osnovata se namirat survurite ot root hints faila. Te obsluzhvat root domeina . (tochka), kakto e vidno i ot sledniia primer:

# host -t soa . c.root-servers.net
Using domain server:
Name: c.root-servers.net
Address: 192.33.4.12#53
Aliases:

. has SOA record a.root-servers.net. nstld.verisign-grs.com. 2012091300 1800 900 604800 86400 Tezi dns root survuri sa authoritative samo za . domeina. Za vsichki ostanali, te imat prepratki, kum koito eventualno mogat da znaiat kude se namira SOA zapisut na daden domein.

# dnsq soa .com a.root-servers.net
6 com:
509 bytes, 1+0+13+15 records, response, noerror
query: 6 com
authority: com 172800 NS a.gtld-servers.net
authority: com 172800 NS b.gtld-servers.net
authority: com 172800 NS c.gtld-servers.net
authority: com 172800 NS d.gtld-servers.net
authority: com 172800 NS e.gtld-servers.net
authority: com 172800 NS f.gtld-servers.net
authority: com 172800 NS g.gtld-servers.net
authority: com 172800 NS h.gtld-servers.net
authority: com 172800 NS i.gtld-servers.net
authority: com 172800 NS j.gtld-servers.net
authority: com 172800 NS k.gtld-servers.net
authority: com 172800 NS l.gtld-servers.net
authority: com 172800 NS m.gtld-servers.net
additional: a.gtld-servers.net 172800 A 192.5.6.30
additional: b.gtld-servers.net 172800 A 192.33.14.30
additional: c.gtld-servers.net 172800 A 192.26.92.30
additional: d.gtld-servers.net 172800 A 192.31.80.30
additional: e.gtld-servers.net 172800 A 192.12.94.30
additional: f.gtld-servers.net 172800 A 192.35.51.30
additional: g.gtld-servers.net 172800 A 192.42.93.30
additional: h.gtld-servers.net 172800 A 192.54.112.30
additional: i.gtld-servers.net 172800 A 192.43.172.30
additional: j.gtld-servers.net 172800 A 192.48.79.30
additional: k.gtld-servers.net 172800 A 192.52.178.30
additional: l.gtld-servers.net 172800 A 192.41.162.30
additional: m.gtld-servers.net 172800 A 192.55.83.30
Kakto e vidno, za TLD ima 13 survura, koito sa imenuvani po podobie na root survurite, a te sa [a-m].gtld-servers.net.

Domeinite ot tipa .com, .net, .org se narichat Top-level Domains (TLD), kato spetsifichnite domeini na durzhavi kato .bg, .de i t.n. se narichat Country Code Top-Level Domains (ccTLD).

GLUE zapisi

Kogato authoritative DNS survurite na dadena zona (example.com) sa v samata zona (ns1.example.com, ns2.example.com,...), se poluchava problem s otkrivaneto na IP adresite im.
Za tova e nuzhno, pri registratsiiata na domein, da se zadadat taka narechenite GLUE zapisi (dopulnitelen A zapis), koito sa dopulnitelni zapisi s IP adresite na authoritative dns survurite za dadenniia domein, po sledniia nachin:
ns1.example.com 123.123.123.1
ns2.example.com 123.222.123.2 GLUE - zapisite mogat da se diagnostitsirat chrez niakoi ot dostupnite po mrezhata DNS instrumenti kato http://www.webdnstools.com/dnstools/domain_check , ili chrez programkite dnstrace, dnstracesort ot paketa djbdns. Dnstrace zapochva ot root survurite i sledva vsichki prepratki za dadeniia domein. Izhodut na programata e dosta obemist, za tova shte pokazhem samo malka chast ot nego:
# dnstrace ns google.com b.root-servers.net | dnstracesort > google.com.txt
# ls -la google.com.txt
-rw-r--r-- 1 root wheel 726714 Sep 14 10:54 google.com

zabelezhka: DNS survurite na google.com sa ot mrezhata 216.239.3hh.hhh za tova pravia izvadka samo na tezi IP-ta ot dnstrace.

# cat google.com.txt|grep 216.239.3 - [cut ] - 1 ns1.google.com 216.239.32.10 345600 A 216.239.32.10
1 ns2.google.com 216.239.32.10 345600 A 216.239.34.10
1 ns3.google.com 216.239.32.10 345600 A 216.239.36.10
1 ns4.google.com 216.239.38.10 345600 A 216.239.38.10
...
glue google.com 216.239.32.10 NS ns1.google.com
glue google.com 216.239.32.10 NS ns2.google.com
glue google.com 216.239.32.10 NS ns3.google.com
glue google.com 216.239.32.10 NS ns4.google.com
...
glue ns1.google.com 192.12.94.30 A 216.239.32.10
glue ns1.google.com 192.26.92.30 A 216.239.32.10
glue ns1.google.com 192.31.80.30 A 216.239.32.10
glue ns1.google.com 192.33.14.30 A 216.239.32.10
glue ns1.google.com 192.35.51.30 A 216.239.32.10
glue ns1.google.com 192.41.162.30 A 216.239.32.10
glue ns1.google.com 192.42.93.30 A 216.239.32.10
glue ns1.google.com 192.43.172.30 A 216.239.32.10
glue ns1.google.com 192.48.79.30 A 216.239.32.10
glue ns1.google.com 192.5.6.30 A 216.239.32.10
glue ns1.google.com 192.52.178.30 A 216.239.32.10
glue ns1.google.com 192.54.112.30 A 216.239.32.10
glue ns1.google.com 192.55.83.30 A 216.239.32.10
glue ns1.google.com 216.239.32.10 A 216.239.32.10
glue ns1.google.com 216.239.34.10 A 216.239.32.10
glue ns1.google.com 216.239.36.10 A 216.239.32.10
glue ns1.google.com 216.239.38.10 A 216.239.32.10
...
- [ cut ] -
Kakto se vizhda tozi red "glue ns1.google.com 192.12.94.30 A 216.239.32.10" dns survurut 192.12.94.30 ima dopulnitelen A (glue) zapis za ns1.google.com koito e 216.239.32.10. IP adresa 192.12.94.30 vsushtnost e edin ot global TLD survurite:

# host 192.12.94.30
30.94.12.192.in-addr.arpa domain name pointer e.gtld-servers.net.
Poveche informatsiia za GLUE zapisite: http://tools.ietf.org/html/draft-koch-dns-glue-clarifications-04

Reverse DNS (PTR zapisi)

Tova e taka narecheniiat "obraten resolving", na koi hostname otgovaria dadeniiat IP adres. Tova na praktika e edin spetsialen domein, koito se naricha in-addr.arpa.

# dnsq soa arpa f.root-servers.net
6 arpa:
508 bytes, 1+1+12+13 records, response, authoritative, noerror
query: 6 arpa
answer: arpa 86400 SOA a.root-servers.net nstld.verisign-grs.com 2012091400 1800 900 604800 86400
authority: arpa 518400 NS c.root-servers.net
authority: arpa 518400 NS d.root-servers.net
authority: arpa 518400 NS m.root-servers.net
authority: arpa 518400 NS i.root-servers.net
authority: arpa 518400 NS f.root-servers.net
authority: arpa 518400 NS l.root-servers.net
authority: arpa 518400 NS h.root-servers.net
authority: arpa 518400 NS k.root-servers.net
authority: arpa 518400 NS g.root-servers.net
authority: arpa 518400 NS b.root-servers.net
authority: arpa 518400 NS e.root-servers.net
authority: arpa 518400 NS a.root-servers.net
- [ cut ] -
Za Top-Level domeina ARPA authritative dns survuri sa root dns survurite

# dnsq soa in-addr.arpa f.root-servers.net
6 in-addr.arpa:
406 bytes, 1+0+6+12 records, response, noerror
query: 6 in-addr.arpa
authority: in-addr.arpa 172800 NS e.in-addr-servers.arpa
authority: in-addr.arpa 172800 NS c.in-addr-servers.arpa
authority: in-addr.arpa 172800 NS f.in-addr-servers.arpa
authority: in-addr.arpa 172800 NS b.in-addr-servers.arpa
authority: in-addr.arpa 172800 NS a.in-addr-servers.arpa
authority: in-addr.arpa 172800 NS d.in-addr-servers.arpa
additional: a.in-addr-servers.arpa 172800 A 199.212.0.73
additional: b.in-addr-servers.arpa 172800 A 199.253.183.183
additional: c.in-addr-servers.arpa 172800 A 196.216.169.10
additional: d.in-addr-servers.arpa 172800 A 200.10.60.53
additional: e.in-addr-servers.arpa 172800 A 203.119.86.101
additional: f.in-addr-servers.arpa 172800 A 193.0.9.1
Za domeina in-addr.arpa dns survurite sa [a-f].in-addr.servers.arpa kakto i glue zapisite kum tiah.

# dnsq ns in-addr.arpa e.in-addr-servers.arpa
2 in-addr.arpa:
142 bytes, 1+6+0+0 records, response, authoritative, noerror
query: 2 in-addr.arpa
answer: in-addr.arpa 86400 NS d.in-addr-servers.arpa
answer: in-addr.arpa 86400 NS f.in-addr-servers.arpa
answer: in-addr.arpa 86400 NS a.in-addr-servers.arpa
answer: in-addr.arpa 86400 NS b.in-addr-servers.arpa
answer: in-addr.arpa 86400 NS e.in-addr-servers.arpa
answer: in-addr.arpa 86400 NS c.in-addr-servers.arpa
Tuk veche poluchihme dostoverna informatsiia za in-addr.arpa dns survurite.

Zonite v domeina in-addr.arpa se sustoiat ot IP adresite na mrezhite na koito shte se praviat PTR zapisi. Razlikata e che mrezhite se pishat v obraten red. Primer za mrezhata 216.239.32.0/24:

# dnsq soa 32.239.216.in-addr.arpa a.in-addr-servers.arpa
6 32.239.216.in-addr.arpa:
177 bytes, 1+0+8+0 records, response, noerror
query: 6 32.239.216.in-addr.arpa
authority: 216.in-addr.arpa 86400 NS u.arin.net
authority: 216.in-addr.arpa 86400 NS w.arin.net
authority: 216.in-addr.arpa 86400 NS t.arin.net
authority: 216.in-addr.arpa 86400 NS v.arin.net
authority: 216.in-addr.arpa 86400 NS z.arin.net
authority: 216.in-addr.arpa 86400 NS y.arin.net
authority: 216.in-addr.arpa 86400 NS r.arin.net
authority: 216.in-addr.arpa 86400 NS x.arin.net

# dnsq soa 32.239.216.in-addr.arpa u.arin.net
6 32.239.216.in-addr.arpa:
123 bytes, 1+0+4+0 records, response, noerror
query: 6 32.239.216.in-addr.arpa
authority: 32.239.216.in-addr.arpa 86400 NS ns4.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns2.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns3.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns1.google.com

# dnsq soa 32.239.216.in-addr.arpa ns1.google.com
6 32.239.216.in-addr.arpa:
233 bytes, 1+1+4+4 records, response, authoritative, weird rd, noerror
query: 6 32.239.216.in-addr.arpa
answer: 32.239.216.in-addr.arpa 86400 SOA ns1.google.com dns-admin.google.com 2012082800 21600 3600 1209600 10800
authority: 32.239.216.in-addr.arpa 86400 NS ns1.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns2.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns4.google.com
authority: 32.239.216.in-addr.arpa 86400 NS ns3.google.com
additional: ns1.google.com 345600 A 216.239.32.10
additional: ns2.google.com 345600 A 216.239.34.10
additional: ns4.google.com 345600 A 216.239.38.10
additional: ns3.google.com 345600 A 216.239.36.10 Kakto se vizhda po-gore, zonata za mrezhata 216.239.32.h (32.239.216.in-addr.arpa) e delegirana kum ns1.google.com.

Za poveche informatsiia mozhete da prochetete RFC2317 - Classless in-addr.arpa delegaion.

Authoritative DNS survur

Authoritative DNS survur e survur, koito e konfiguriran da otgovaria na zapitvaniia za dadeni domeini. Toi ne izpulniava recursive dns zapitvaniia, i e strogo ogranichen samo do otgovori za predvaritelno konfiguriranite domeini.

Tuk triabva da se otbelezhi oburkvaneto i smesvaneto na poniatiiata "dns cache" i "authoritative dns survur", dulzhashto se na nai-razprostranata implementatsiia na dns survur - BIND.
Dobrite praktiki za sigurnost pokazvat, che authoritative dns i dns cache survurite triabva da sa otdelni programi, startirani kato otdelni protsesi, slushashti na otdelni IP adresi. Pri BIND, dvata survura sa v edin protses. CHak ot BIND 10 tezi survuri shte budat otdelni protsesi.

Eto primer za otgovori:

pitame dns cache survur (10.1.42.1) za dva dns zapisa - www.google.com i www.linux-bg.org

# host www.google.com 10.1.42.1
Using domain server:
Name: 10.1.42.1
Address: 10.1.42.1#53
Aliases:

www.google.com is an alias for www.l.google.com.
www.l.google.com has address 173.194.35.144
www.l.google.com has address 173.194.35.148
www.l.google.com has address 173.194.35.147
www.l.google.com has address 173.194.35.145
www.l.google.com has address 173.194.35.146

# host www.linux-bg.org 10.1.42.1
Using domain server:
Name: 10.1.42.1
Address: 10.1.42.1#53
Aliases:

www.linux-bg.org has address 212.50.10.155 pitame authoritative dns survur (v sluchaia ns1.google.com za zonata google.com) za www.google.com i www.linux-bg.org.

# host www.google.com ns1.google.com
Using domain server:
Name: ns1.google.com
Address: 216.239.32.10#53
Aliases:

www.google.com is an alias for www.l.google.com.
www.l.google.com has address 173.194.35.148
www.l.google.com has address 173.194.35.147
www.l.google.com has address 173.194.35.145
www.l.google.com has address 173.194.35.144
www.l.google.com has address 173.194.35.146

# host www.linux-bg.org ns1.google.com
Using domain server:
Name: ns1.google.com
Address: 216.239.32.10#53
Aliases:

Host www.linux-bg.org not found: 5(REFUSED)
Vidno e, che pri vtoroto zapitvane otgovorut e REFUSED. Tova pokazva, che ns1.google.com ne izpulniava recursive zapitvaniia i otgovaria samo za google.com zonata (kakto i za drugi zoni za koito e konfiguriran da e authoritative).

Preporuki za authoritative dns

Tui kato dns e mnogo chuvstvitelen ot kum burzinata na dostup, ima niakolko iziskvaniia, predi da si instalirame authoritative dns survur za obsluzhvane na lichen domein.

* preporuchitelno e da imate 2 IP adresa ot razlichni mrezhi, svurzani s razlichni dostavchitsi;
* skorostta triabva da e garantirana do izvestna stepen v dvete posoki;
* prekusvaniiata na interneta da budat vuzmozhno nai-malki.


Ako ne mozhete da osigurite tezi iziskvaniia, Vi preporuchvam da izpolzvate za dns hosting survurite na firmata, ot koiato ste zakupili dadeniia domein, osven ako ne ste entusiast i iskate da se nauchite.

Konfiguratsionniiat fail na edin authoritative dns survur se sustoi ot otdelni "zoni", koito na praktika predstavliavat spisuk s Resource Records za daden domein. Vsiaka zona triabva da sudurzha:

* SOA - zapis - master.dns.domain.com, email.za.kontakti.domain.com, serien nomer, refresh, retry, expire, min TTL.
master dns - osnoven dns survur.
email - emeil za kontakti pri problemi s tozi domein.
serial - serien nomer chrez koito se razbira po dannite na domeina ima promeni. Preporuchitelno da tekushtata data na promenite vuv format: DDMMYYYYX, kudeto X e broi promeni za denia.
refresh - sled kolko sekundi slave dns survura shte se opita da obnovi dannite si ot master dns.
retry - pri problem, sled kolko sekundi slave dns survura shte se opita otnovo da opresni dannite ot master dns.
expire - pri problem s obnovlenieto, sled kolko sekundi slave dns survura shte spre da otgovaria na zapitvaniia za dadeniia domein, tui kato dannite shte budat smiatani za ostareli.
* NS - zapis - minimun edin, ot tipa ns1.domain.com
* A - zapis - A zapis za ns1 kum domain.com
ako domeina shte poluchava poshta, e nuzhen i pone edin:
* MX - zapis - hostname, kudeto shte se namira meil survurite obsluzhvashti domain.com, naprimer mail.domain.com. Mozhe da imate poveche ot edin mx zapis, kato prioriteta im se ukazva chrez chislo, pri koeto kolkoto e po-niska stoinostta, e s po-goliam prioritet. Primer:

# dnsq mx google.com ns1.google.com
15 google.com:
216 bytes, 1+5+0+5 records, response, authoritative, weird rd, noerror
query: 15 google.com
answer: google.com 600 MX 20 alt1.aspmx.l.google.com
answer: google.com 600 MX 10 aspmx.l.google.com
answer: google.com 600 MX 50 alt4.aspmx.l.google.com
answer: google.com 600 MX 30 alt2.aspmx.l.google.com
answer: google.com 600 MX 40 alt3.aspmx.l.google.com
Kakto se vizhda ot primera po-gore, s nai-goliam prioritet ot tezi meil survuri e aspmx.l.google.com, koito e s nai-niska stoinost (10), a s nai-nisuk prioritet e alt4.aspmx.l.google.com (50).

* A - zapis - za mail.domain.com kum koe IP sochi
ako domeina shte bude dostupen prez web survur e nuzhen zapis:
* A - zapis - A zapis za www kum domeina domain.com, toest na koe IP otgovaria www.domain.com.
* TXT - preporuchitelno e da se izpolzva za SPF zapis, kogato ima konfigurirani MX zapisi (www.openspf.org).

* Prazen A - zapis - tova ne nuzhno, za da raboti web survura (primerno www.domain.com), kogato potrebitelite ne pishat www.domain.com, a samo domain.com

Primer za tova kak izglezhda edna standartno konfigurirana zona:
Zona example.com ns1.example.com. hostmaster.example.com. 2012010601 3600 600 120960 3600 3600
NS zapis ns1.example.com 3600
NS zapis ns2.example.com 3600
MX zapis mail1.example.com 10 86400
MX zapis mail2.example.com 100 86400
A zapis ns1.example.com 193.22.103.226 3600
A zapis ns2.example.com 193.22.103.2 3600
A zapis example.com 195.177.249.170 3600
A zapis mail1.example.com 195.177.249.170 3600
A zapis mail2.example.com 195.177.249.170 3600
A zapis archive.example.com 195.177.249.170 3600
A zapis blog.example.com 195.177.249.170 3600
A zapis www.example.com 195.177.249.170 86400
TXT zapis za SPF "v=spf1 mx a:mail1.example.com a:mail2.example.com -all"

Za da imame sobstveni DNS survuri kato za nachalo e nuzhno da si zakupim domein. Tova stava ot suotvetnata firma, predlagashta tazi uslga. Tova koeto triabva da napravite pri registratsiiata, e da dobavite 2 DNS survura, kakto i GLUE zapisite kum tiah.
Ako sme zakupili domeina example.com, triabva da vuvedem i DNS survurite, koito shte obsluzhvat tozi domein zaedno s tehnite IP adresi v administrativniia panel za DNS na saita, ot koito sme kupili domeina. Naprimer:
ns1.example.com 193.32.12.1
ns2.example.com 193.52.50.1 Ot tuk natatuk triabva da imame instalirani DNS survuri na tezi IP adresi kato te triabva da budat konfigurirani da obsluzhvat domeina example.com (da sa authoritative za example.com).
Primerni instalatsiia i konfiguratsiia na tezi survuri shte bude razgledano v tretata chast na tazi poreditsa ot statii za DNS.

Lame nameservers

Tova sa DNS survuri, koito sa posocheni za authoritative dns za daden domein, no ne sa konfigurirani da otgovariat na zapitvaniia za tozi domein. S drugi dumi, te vrushtat otgovor ot tipa - refused. Eto primer za lame nameserver:

Koi sa dns survurite, obsluzhvashti zonata cnsys.bg?

# host -t ns cnsys.bg
cnsys.bg name server ns.btc-net.bg.
cnsys.bg name server ns2.atlantis.bg.
cnsys.bg name server clio.cnsys.bg.
Neka popitame za mx - zapis kum domeina cnsys.bg. Purvo pitame ns.btc-net.bg.

# host -t mx cnsys.bg ns.btc-net.bg.
Using domain server:
Name: ns.btc-net.bg.
Address: 212.39.90.73#53
Aliases:

cnsys.bg mail is handled by 10 clio.cnsys.bg.
Da popitame vtoriiat DNS survur (ns2.atlantis.bg) za sushtoto:

# host -t mx cnsys.bg ns2.atlantis.bg.
Using domain server:
Name: ns2.atlantis.bg.
Address: 193.108.24.4#53
Aliases:

Host cnsys.bg not found: 5(REFUSED) Kakto se vizhda, vupreki, che ns2.atlantis.bg e v spisuka s dns survuri obsluzhvashti cnsys.bg, pri zapitvane kum nego za mx zapis otgovorut e REFUSED, toest konfiguratsiiata e nepravilna, i ns2.atlantis.bg ne otgovaria na zapitvaniia za zonata cnsys.bg, vureki, che firurira v spisuka kato authoritative. V tozi sluchai tozi dns survur se vodi lame za zonata cnsys.bg.

Kak da instalirame i konfigurirame authoritative dns survur shte razgledame v sledvashtata chast na tazi poreditsa statii.

Tazi statiia e publikuvana i v bloga na svoia avtor: Kak raboti DNS, chast 2 - Topologiia, Authoritative servers



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