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The resolving name servers directly finds out information about the root servers, top level domains and authoritative name servers. It also speed up queries by caching results locallly as configured by hostmater in their domains’ TTL field. You can setup BIND 9 as caching name server to speed up dns caching for the rest of all clients. This tutorial explains:

  1. How to install BIND 9 caching only dns server under Debian Linux
  2. BIND 9 troubleshooting tips
  3. Iptables firewall configuration

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How do I edit /etc/resolv.conf file in CentOS Linux?
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What Is NXDOMAIN?

What is NXDOMAIN? How does nxdomain affects my browsing? Explains the relationship between NXDOMAIN and DNS Hijacking.
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Wikipedia.org is one of the busiest website on the Internet went down today due to DNS issues. From the official blog post:

Due to an overheating problem in our European data center many of our servers turned off to protect themselves. As this impacted all Wikipedia and other projects access from European users, we were forced to move all user traffic to our Florida cluster, for which we have a standard quick failover procedure in place, that changes our DNS entries. However, shortly after we did this failover switch, it turned out that this failover mechanism was now broken, causing the DNS resolution of Wikimedia sites to stop working globally. This problem was quickly resolved, but unfortunately it may take up to an hour before access is restored for everyone, due to caching effects.

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25 Years Of The .com

The domain name .com is a generic top-level domain (gTLD) in the Domain Name System of the Internet. .COM is one of the first set of gTLD. It was first implemented for use on the Internet in January 1985. The internet celebrates a landmark event on the 15 March – the 25th birthday of the day the first dotcom name was registered. The following are the 100 oldest still-existing registered .com domains:

1. 	15-Mar-1985 	SYMBOLICS.COM
2. 	24-Apr-1985 	BBN.COM
3. 	24-May-1985 	THINK.COM
4. 	11-Jul-1985 	MCC.COM
5. 	30-Sep-1985 	DEC.COM
6. 	07-Nov-1985 	NORTHROP.COM
7. 	09-Jan-1986 	XEROX.COM
8. 	17-Jan-1986 	SRI.COM
9. 	03-Mar-1986 	HP.COM
10. 	05-Mar-1986 	BELLCORE.COM
11. 	19-Mar-1986 	IBM.COM
12. 	19-Mar-1986 	SUN.COM
13. 	25-Mar-1986 	INTEL.COM
14. 	25-Mar-1986 	TI.COM
15. 	25-Apr-1986 	ATT.COM
16. 	08-May-1986 	GMR.COM
17. 	08-May-1986 	TEK.COM
18. 	10-Jul-1986 	FMC.COM
19. 	10-Jul-1986 	UB.COM
20. 	05-Aug-1986 	BELL-ATL.COM
21. 	05-Aug-1986 	GE.COM
22. 	05-Aug-1986 	GREBYN.COM
23. 	05-Aug-1986 	ISC.COM
24. 	05-Aug-1986 	NSC.COM
25. 	05-Aug-1986 	STARGATE.COM
26. 	02-Sep-1986 	BOEING.COM
27. 	18-Sep-1986 	ITCORP.COM
28. 	29-Sep-1986 	SIEMENS.COM
29. 	18-Oct-1986 	PYRAMID.COM
30. 	27-Oct-1986 	ALPHACDC.COM
31. 	27-Oct-1986 	BDM.COM
32. 	27-Oct-1986 	FLUKE.COM
33. 	27-Oct-1986 	INMET.COM
34. 	27-Oct-1986 	KESMAI.COM
35. 	27-Oct-1986 	MENTOR.COM
36. 	27-Oct-1986 	NEC.COM
37. 	27-Oct-1986 	RAY.COM
38. 	27-Oct-1986 	ROSEMOUNT.COM
39. 	27-Oct-1986 	VORTEX.COM
40. 	05-Nov-1986 	ALCOA.COM
41. 	05-Nov-1986 	GTE.COM
42. 	17-Nov-1986 	ADOBE.COM
43. 	17-Nov-1986 	AMD.COM
44. 	17-Nov-1986 	DAS.COM
45. 	17-Nov-1986 	DATA-IO.COM
46. 	17-Nov-1986 	OCTOPUS.COM
47. 	17-Nov-1986 	PORTAL.COM
48. 	17-Nov-1986 	TELTONE.COM
49. 	11-Dec-1986 	3COM.COM
50. 	11-Dec-1986 	AMDAHL.COM
51. 	11-Dec-1986 	CCUR.COM
52. 	11-Dec-1986 	CI.COM
53. 	11-Dec-1986 	CONVERGENT.COM
54. 	11-Dec-1986 	DG.COM
55. 	11-Dec-1986 	PEREGRINE.COM
56. 	11-Dec-1986 	QUAD.COM
57. 	11-Dec-1986 	SQ.COM
58. 	11-Dec-1986 	TANDY.COM
59. 	11-Dec-1986 	TTI.COM
60. 	11-Dec-1986 	UNISYS.COM
61. 	19-Jan-1987 	CGI.COM
62. 	19-Jan-1987 	CTS.COM
63. 	19-Jan-1987 	SPDCC.COM
64. 	19-Feb-1987 	APPLE.COM
65. 	04-Mar-1987 	NMA.COM
66. 	04-Mar-1987 	PRIME.COM
67. 	04-Apr-1987 	PHILIPS.COM
68. 	23-Apr-1987 	DATACUBE.COM
69. 	23-Apr-1987 	KAI.COM
70. 	23-Apr-1987 	TIC.COM
71. 	23-Apr-1987 	VINE.COM
72. 	30-Apr-1987 	NCR.COM
73. 	14-May-1987 	CISCO.COM
74. 	14-May-1987 	RDL.COM
75. 	20-May-1987 	SLB.COM
76. 	27-May-1987 	PARCPLACE.COM
77. 	27-May-1987 	UTC.COM
78. 	26-Jun-1987 	IDE.COM
79. 	09-Jul-1987 	TRW.COM
80. 	13-Jul-1987 	UNIPRESS.COM
81. 	27-Jul-1987 	DUPONT.COM
82. 	27-Jul-1987 	LOCKHEED.COM
83. 	28-Jul-1987 	ROSETTA.COM
84. 	18-Aug-1987 	TOAD.COM
85. 	31-Aug-1987 	QUICK.COM
86. 	03-Sep-1987 	ALLIED.COM
87. 	03-Sep-1987 	DSC.COM
88. 	03-Sep-1987 	SCO.COM
89. 	22-Sep-1987 	GENE.COM
90. 	22-Sep-1987 	KCCS.COM
91. 	22-Sep-1987 	SPECTRA.COM
92. 	22-Sep-1987 	WLK.COM
93. 	30-Sep-1987 	MENTAT.COM
94. 	14-Oct-1987 	WYSE.COM
95. 	02-Nov-1987 	CFG.COM
96. 	09-Nov-1987 	MARBLE.COM
97. 	16-Nov-1987 	CAYMAN.COM
98. 	16-Nov-1987 	ENTITY.COM
99. 	24-Nov-1987 	KSR.COM
100. 	30-Nov-1987 	NYNEXST.COM

(Source: 100 Oldest Domain )

Gathering Information About Old Domain Names

UNIX and OS X users can type the following commands to grab more information about these domain names without visiting any 3rd party websites:

Find Whois Information

Type the following command:
whois domainName
whois SYMBOLICS.COM

Sample outputs:

Registrant:
Meystedt, Aron
   XF.com Company
   PO BOX 293
   Cape Girardeau, MO 63702
   US
   Domain Name: SYMBOLICS.COM
   ------------------------------------------------------------------------
   Promote your business to millions of viewers for only $1 a month
   Learn how you can get an Enhanced Business Listing here for your domain name.
   Learn more at http://www.NetworkSolutions.com/
   ------------------------------------------------------------------------
   Administrative Contact, Technical Contact:
      Meystedt, Aron		admin.noSPAM at XF.com
      XF.com Company
      PO BOX 293
      Cape Girardeau, MO 63702
      US
      573-450-8272
   Record expires on 16-Mar-2016.
   Record created on 15-Mar-1985.
   Database last updated on 15-Mar-2010 13:08:00 EDT.
   Domain servers in listed order:
   NS1.AMERINOC.COM
   NS2.AMERINOC.COM

Get IP Address And Other Information

List name server:
host -t ns SYMBOLICS.COM
List mail servers:
host -t mx SYMBOLICS.COM
List IPv4 and IPv6 address:
host -t A SYMBOLICS.COM
host -t AAAA SYMBOLICS.COM

Query For Any Type Of Record Information

dig any SYMBOLICS.COM
Sample outputs:

; <<>> DiG 9.6.1-P2 <<>> any SYMBOLICS.COM
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18452
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 2, ADDITIONAL: 0
;; QUESTION SECTION:
;SYMBOLICS.COM.			IN	ANY
;; ANSWER SECTION:
SYMBOLICS.COM.		14364	IN	SOA	ns1.phatservers.COM. root.SYMBOLICS.COM. 2009091401 14400 3600 1209600 86400
SYMBOLICS.COM.		7799	IN	A	64.6.107.133
SYMBOLICS.COM.		7799	IN	NS	ns1.phatservers.COM.
SYMBOLICS.COM.		7799	IN	NS	ns2.phatservers.COM.
;; AUTHORITY SECTION:
SYMBOLICS.COM.		7799	IN	NS	ns2.phatservers.COM.
SYMBOLICS.COM.		7799	IN	NS	ns1.phatservers.COM.
;; Query time: 33 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Mar 15 22:47:47 2010
;; MSG SIZE  rcvd: 164

Request A Zone Transfer

Type the following command (this may not work if you are not on authorized slave server, in most case this is blocked by hostmaster):
dig @ns1.example.com example.com axfr

Shell And Perl Script Hacks

You can put all old domain names in a text file and run some commands over all old domains:

#!/bin/bash
input=100old.txt
while -r domain
do
   echo "Do something on $domain"
   # host -t ns $domain
done <"$input"

Net::DNS is a DNS resolver implemented in Perl. It allows the programmer to perform nearly any type of DNS query from a Perl script. Here is a sample perl script to find out name server address:

#!/usr/bin/perl -w
  use Net::DNS;
  $res = new Net::DNS::Resolver;
  $query = $res->query("IBM.COM", "NS");
  if ($query) {
      foreach $rr ($query->answer) {
          next unless $rr->type eq "NS";
          print $rr->nsdname, "\n";
      }
  }
  else {
      print "query failed: ", $res->errorstring, "\n";
  }
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CentOS: Use OpenDNS To Resolve Hostnames

How do I use OpenDNS server for my CentOS Linux vps or dedicated server to resolve hostnames?
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Ubuntu: Set OpenDNS DNS Server

How do I set OpenDNS DNS server under Ubuntu Linux desktop operating systems by editing configuration files?
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What Is Round Robin DNS?

Round robin DNS is nothing but a simple technique of load balancing various Internet services such as Web server, e-mail server by creating multiple DNS A records with the same name.

How Does It Works?

You configure DNS server to send a list of IP addresses of several servers with same hostname. For example, foo.dnsknowledge.com may be configured to return two IP address as follows:

  • foo.dnsknowledge.com – 202.54.1.2
  • foo.dnsknowledge.com – 202.54.1.3

Half of the time when a user make foo.dnsknowledge.com request will go to 202.54.1.2 and rest will go to 202.54.1.3. In other words, all clients would receive service from two different server, thus distributing the overall load among servers.

Round Robin DNS Usage

You can use round robin DNS for

  1. Load distribution.
  2. Load balancing.
  3. Fault-tolerance service.

Round Robin DNS Example

Open a terminal (Mac OS X or UNIX / Linux) and type the following command to see IP address of google.com:
host -t A google.com
Sample outputs:

google.com has address 74.125.53.100
google.com has address 74.125.45.100
google.com has address 74.125.67.100

So a request to google.com would be split into the 3 server. When you type http://google.com/ first time in a browser, 74.125.53.100 will display google search home page. Type the following command again at the shell prompt:
host -t A google.com
Sample outputs:

google.com has address 74.125.67.100
google.com has address 74.125.53.100
google.com has address 74.125.45.100

Next request would go to the server 74.125.67.100. By using Round Robin DNS google managed to lighten the webserver load. This kind of setup pretty common among the large website such as google.com, amazon.com, yahoo.com etc. If your site gets a large number of hits (millions of unique hits per day) per day, consider using this technique.

Suggested Readings:

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I see the following error in my /var/log/messages file under Linux operating systems running BIND 9 master name server:

May 25 15:43:29 ns1 named[11794]: general: info: loading configuration from ‘/etc/named.conf’
May 25 15:43:29 ns1 named[11794]: general: info: using default UDP/IPv4 port range: [1024, 65535]
May 25 15:43:29 ns1 named[11794]: general: info: using default UDP/IPv6 port range: [1024, 65535]
May 25 15:43:29 ns1 named[11794]: general: error: the working directory is not writable
May 25 15:43:29 ns1 named[11794]: general: error: zone example.org/IN/external: zone serial has gone backwards
May 25 15:43:29 ns1 named[11794]: general: info: zone example.org/IN/external: loaded serial 2008090814
May 25 15:43:29 ns1 named[11794]: notify: info: zone example.org/IN/external: sending notifies (serial 2008090814)

How do I fix this problem under BIND 9 named server?
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What is Time To Live (TTL)?

Time to live (TTL) is used for computer data including DNS servers. It is nothing but time on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e.g. a packet) can experience before it should be discarded.
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