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NSLOOKUP March 2009 ITCJay Hall

NEA-SEA ITC 2009

Quick DNS Record Type Review

• A– Maps a host name to an IPv4 address.

• CNAME– Alias of one name to another (canonical name).

• MX– Mail eXchanger record.

Quick DNS Record Type Review

• NS– Authoritative Name Server for the zone.

• PTR– PoinTer Record. Only returns a name. Commonly

used for reverse DNS.

What is nslookup?

• Used in Windows and *NIX systems to query DNS servers to find– details of the zone

• including IP addresses.• A, MX and other records for the zone• primary name server addresses for the zone.

Using nslookup

• nslookup has two modes– command line and – interactive.

• Personally, I think interactive mode is easier to use.– Mainly because I cannot remember the command

line parameters.

nslookup commands

• server aa.dd.re.ss– IP address, or name, of the server to use for DNS

queries.

• set – domain=name

• set a default domain name.

– type• type of record to search for.• A, ANY, CNAME, MX, NS, PTR, SOA.

nslookup commands

• server name– Use the specified server for queries. Can be an IP

address or a name.

• ls (Windows only)– List the addresses in the domain.– -t specifies the type to list.

nslookup examplesjhall@jefmhallja-~$ nslookup> set type=mx> server 10.129.10.41Default server: 10.129.10.41Address: 10.129.10.41#53> server mo-hq-s1.mo.locDefault server: mo-hq-s1.mo.locAddress: 10.129.10.41#53> mnea.orgServer: mo-hq-s1.mo.locAddress: 10.129.10.41#53mnea.org mail exchanger = 20 mail2.mnea.org.mnea.org mail exchanger = 10 mo-hq-s1.mo.loc.>

nslookup examples

jhall@jefmhallja-~$ nslookup -type=mx mnea.org mo-hq-s1.mo.loc

Server: mo-hq-s1.mo.loc

Address: 10.129.10.41#53

mnea.org mail exchanger = 10 mo-hq-s1.mo.loc.

mnea.org mail exchanger = 20 mail2.mnea.org.

nslookup examples

> set type=a

> mail.mnea.org

Server: ns3.socket.net

Address:70.246.240.169#53

Non-authoritative answer:

Name: mail.mnea.org

Address: 65.117.48.157

nslookup examples

> server mo-hq-s1.mo.loc

Default server: mo-hq-s1.mo.loc

Address: 10.129.10.41#53

> mail.mnea.org

Server: mo-hq-s1.mo.loc

Address:10.129.10.41#53

Name: mail.mnea.org

Address: 10.129.10.45

What is Dig?

• Domain Information Groper

• Has the same uses as nslookup.

• ISC is slowly replacing nslookup with dig due to security concerns.

• In my opinion, dig is easier to use.

Dig Commands and Examples

• dig @server name type– Type can be any valid DNS record type.

• Dig has a special query type called axfr.– This initiates a zone transfer so all of the zone data

can be seen.

– Some servers do not allow this.

Dig Commands and Examples

;; QUESTION SECTION:;mnea.org. IN A

;; ANSWER SECTION:mnea.org. 900 IN A 65.117.48.158

;; AUTHORITY SECTION:mnea.org. 900 IN NS dca-ans-01.inet.qwest.net.mnea.org. 900 IN NS svl-ans-01.inet.qwest.net.

;; ADDITIONAL SECTION:dca-ans-01.inet.qwest.net. 3600 IN A 205.171.9.242svl-ans-01.inet.qwest.net. 3600 IN A 205.171.14.195

;; Query time: 107 msec;; SERVER: 205.171.9.242#53(205.171.9.242);; WHEN: Wed Feb 25 05:34:06 2009;; MSG SIZE rcvd: 138

Dig Commands and Examples;; QUESTION SECTION:;mnea.org. IN MX

;; ANSWER SECTION:mnea.org. 900 IN MX 5 mail.mnea.org.

;; AUTHORITY SECTION:mnea.org. 900 IN NS dca-ans-01.inet.qwest.net.mnea.org. 900 IN NS svl-ans-01.inet.qwest.net.

;; ADDITIONAL SECTION:mail.mnea.org. 900 IN A 65.117.48.157dca-ans-01.inet.qwest.net. 3600 IN A 205.171.9.242svl-ans-01.inet.qwest.net. 3600 IN A 205.171.14.195

;; Query time: 97 msec;; SERVER: 205.171.9.242#53(205.171.9.242);; WHEN: Wed Feb 25 05:49:26 2009;; MSG SIZE rcvd: 159

Why are DNS tools useful?

• Comparing results between servers.– Internal v. external– Ensuring zone data has propagated from primary

to secondary name servers.– Troubleshooting web access problems.

A better way?There has to be a better way to this.

There is.

http://www.dnsstuff.com

Thank you to DNSStuff for their donation of two one year memberships.

DNSStuff.com

Demonstration

The End