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How does the system DNS - Domain Name System

Because whoever entered the Internet and accessed a website, used and default DNS system, I want to do an introduction about what DNS, and can get in some more technical details.

So the Internet is a network of networks where each network has an address and each network client (PC / router, etc.) are identified by IP address. Internet only works on the real IP address. An IP address is a sequence of 4 numbers from 0-255 separated by a period - for example 193.236.56.89

To see a site but it's hard to remember these numbers without any logic. And so came the DNS system that is responsible for the association between known addresses of all the world like www.domeniu.com and IP addresses (and vice versa)

How DNS works

DNS is a client-server (client = one who asks and who answers = server).

The client is called "DNS resolver" and server "DNS server", or "nameserver".

For example we take to help the tool "nslookup" on Windows which enables us to query DNS servers.

In principle an operation to resolve domain publib.boulder.ibm.com goes something like this (although in reality they are involved and caching operations that do not explain here, because they are a little more sophisticated)

• divides the field into its component parts from the top to the bottom: com, ibm, Boulder, publib
• obtain basic list of 13 name servers (root nameservers). It is known, the public , or using nslookup:
  
  C: \> nslookup-query = ns. 82.76.253.115
  Server: dns-cache-rds.ro 3.rcs
  Address: 82.76.253.115
  Non-authoritative answer:
  (Root) nameserver = D.ROOT-SERVERS.NET
  (Root) nameserver = E.ROOT-SERVERS.NET
  (Root) nameserver = F.ROOT-SERVERS.NET
  (Root) nameserver = G.ROOT-SERVERS.NET
  (Root) nameserver = H.ROOT-SERVERS.NET
  (Root) nameserver = I.ROOT-SERVERS.NET
  (Root) nameserver = J.ROOT-SERVERS.NET
  (Root) nameserver = K.ROOT-SERVERS.NET
  (Root) nameserver = L.ROOT-SERVERS.NET
  (Root) nameserver = M.ROOT-SERVERS.NET
  (Root) nameserver = A.ROOT-SERVERS.NET
  (Root) nameserver = B.ROOT-SERVERS.NET
  (Root) nameserver = C.ROOT-SERVERS.NET
  
• to interrogate one of 13 name servers above to obtain nameservers for TLD. com - we D.ROOT-SERVERS.NET nameserver query, which has IP 128.8.10.90
  
  C: \> nslookup-query = ns com 128.8.10.90
  128.in-addr.arpa nameserver = DILL.ARIN.NET
  128.in-addr.arpa nameserver = INDIGO.ARIN.NET
  128.in-addr.arpa nameserver = Z.ARIN.NET
  128.in-addr.arpa nameserver = X.ARIN.NET
  128.in-addr.arpa nameserver = HENNA.ARIN.NET
  128.in-addr.arpa nameserver = CHIA.ARIN.NET
  128.in-addr.arpa nameserver = BASIL.ARIN.NET
  128.in-addr.arpa nameserver = Y.ARIN.NET
  *** Can not find server name for address 128.8.10.90: No information
  Server: Unknown
  Address: 128.8.10.90

  E.GTLD-SERVERS.NET com nameserver =
  K.GTLD-SERVERS.NET com nameserver =
  F.GTLD-SERVERS.NET com nameserver =
  M.GTLD-SERVERS.NET com nameserver =
  D.GTLD-SERVERS.NET com nameserver =
  J.GTLD-SERVERS.NET com nameserver =
  H.GTLD-SERVERS.NET com nameserver =
  C.GTLD-SERVERS.NET com nameserver =
  I.GTLD-SERVERS.NET com nameserver =
  A.GTLD-SERVERS.NET com nameserver =
  B.GTLD-SERVERS.NET com nameserver =
  G.GTLD-SERVERS.NET com nameserver =
  L.GTLD-SERVERS.NET com nameserver =
  A.GTLD-SERVERS.NET internet address = 192.5.6.30
  B.GTLD-SERVERS.NET internet address = 192.33.14.30
  C.GTLD-SERVERS.NET internet address = 192.26.92.30
  D.GTLD-SERVERS.NET internet address = 192.31.80.30
  E.GTLD-SERVERS.NET internet address = 192.12.94.30
  F.GTLD-SERVERS.NET internet address = 192.35.51.30
  G.GTLD-SERVERS.NET internet address = 192.42.93.30
  H.GTLD-SERVERS.NET internet address = 192.54.112.30
  I.GTLD-SERVERS.NET internet address = 192.43.172.30
  J.GTLD-SERVERS.NET internet address = 192.48.79.30
  K.GTLD-SERVERS.NET internet address = 192.52.178.30
  L.GTLD-SERVERS.NET internet address = 192.41.162.30
  M.GTLD-SERVERS.NET internet address = 192.55.83.30
  A.GTLD-SERVERS.NET AAAA IPv6 address = 2001:503: a83e :: 2:30
  B.GTLD-SERVERS.NET AAAA IPv6 address = 2001:503:231 d :: 2:30
  

• to interrogate one of nameservers obtained in the previous step to obtain name servers for the next level, IBM (ibm.com that is). We query A.GTLD-SERVERS.NET, IP: 192.5.6.30:
  
  C: \> nslookup-query = ns ibm.com 192.5.6.30
  (Root) nameserver = h.root-servers.net
  (Root) nameserver = i.root-servers.net
  (Root) nameserver = k.root-servers.net
  (Root) nameserver = c.root-servers.net
  (Root) nameserver = l.root-servers.net
  (Root) nameserver = j.root-servers.net
  (Root) nameserver = e.root-servers.net
  (Root) nameserver = a.root-servers.net
  (Root) nameserver = d.root-servers.net
  (Root) nameserver = g.root-servers.net
  (Root) nameserver = f.root-servers.net
  (Root) nameserver = m.root-servers.net
  (Root) nameserver = b.root-servers.net
  h.root-servers.net internet address = 128.63.2.53
  h.root-servers.net AAAA IPv6 address = 2001:500:1 :: 803f: 235
  i.root-servers.net internet address = 192.36.148.17
  k.root-servers.net internet address = 193.0.14.129
  k.root-servers.net AAAA IPv6 address = 2001:7 fd :: 1
  c.root-servers.net internet address = 192.33.4.12
  l.root-servers.net internet address = 199.7.83.42
  l.root-servers.net AAAA IPv6 address = 2001:500:3 :: 42
  j.root-servers.net internet address = 192.58.128.30
  j.root-servers.net AAAA IPv6 address = 2001:503: C27 :: 2:30
  e.root-servers.net internet address = 192.203.230.10
  a.root-servers.net internet address = 198.41.0.4
  d.root-servers.net internet address = 128.8.10.90
  *** Can not find server name for address 192.5.6.30: No information
  Server: Unknown
  Address: 192.5.6.30

  Non-authoritative answer:
  ibm.com nameserver = internet-server.zurich.ibm.com
  ibm.com nameserver = ns.almaden.ibm.com
  ibm.com nameserver = ns.austin.ibm.com
  ibm.com nameserver = ns.watson.ibm.com
  Internet Internet address = 195.176.20.204 server.zurich.ibm.com
  ns.almaden.ibm.com internet address = 198.4.83.35
  ns.austin.ibm.com internet address = 192.35.232.34ns.watson.ibm.com internet address = 129.34.20.80
  

• to interrogate one of nameservers obtained in the previous step to obtain the next level, boulder (ie boulder.ibm.com). The name server must know how reasonable or any subdomain of. We query so server.zurich.ibm.com Internet, IP: 195.176.20.204:
  
  C: \> nslookup-query = ns boulder.ibm.com 195.176.20.204
  Server: Internet-server.zurich.ibm.com
  Address: 195.176.20.204

  boulder.ibm.com nameserver = rock.boulder.ibm.com
  boulder.ibm.com nameserver = gateway.boulder.ibm.com
  boulder.ibm.com nameserver = ns.watson.ibm.com
  ns.watson.ibm.com internet address = 129.34.20.80
  rock.boulder.ibm.com internet address = 192.147.13.65
  gateway.boulder.ibm.com internet address = 198.17.57.70

• will query a nameserver so obtained in the previous step to obtain the IP address of the next level - publib (ie public.boulder.ibm.com address):
  
  C: \> nslookup-query = a publib.boulder.ibm.com 129.34.20.80
  Server: ns.watson.ibm.com
  Address: 129.34.20.80

  Name: publib.boulder.ibm.com
  Address: 170.225.15.24

Same thing can be obtained by utility dig, there is a version on the net here: http://www.kloth.net/services/dig.php

Also a great site with DNS utility is dnstools.com .

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