how addresses get mapped back to domain names? in-addr.arpa domain

[skywind]

My question is

1) if several domain names on the same IP, when you do the reverse search on the IP, what will be the search result?

2) reverse search using in-addr.arpa domain. But who is manage the in-addr.arpa domain? like the Name Servers, it is a delegated database. The delegated name server have the zone files for the domains on this server. But it seems in-addr.arpa doesn't delegate it to the delegated name servers. The name servers I only have the local machine loop back in-addr.arpa record. So how the in-addr.arpa domain know how to map the IP on my machine back to the domain?

Thanks!

 

[Serbtastic]

1. An nslookup on the IP will result in whatever domain name your ISP has created a PTR record for.

2. You will need to contact your ISP to create a PTR record for your IP pointing back to your domain name.

 

[ChrisAC]

In order to get your reverse range delegated to your DNS server you need to speak to the organisation that is authoratative for the parent domain and have them arrange a sub delegation to you.

Reverse DNS works in exactly the same way as forward DNS (pretty much anyway).

For example, the domain tek-tips.com is delegated to ns.shutter.net (and ns2.shutter.net). We can query the MX record for this and get an IP address;

[chris@uranium chris]$ dig tek-tips.com mx

; <<>> DiG 9.2.1 <<>> tek-tips.com mx
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44611
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 2, ADDITIONAL: 2

;; QUESTION SECTION:
;tek-tips.com. IN MX

;; ANSWER SECTION:
tek-tips.com. 3600 IN MX 300 smtp-in3.nuvox.net.
tek-tips.com. 3600 IN MX 400 smtp-in4.nuvox.net.
tek-tips.com. 3600 IN MX 500 smtp-in5.nuvox.net.
tek-tips.com. 3600 IN MX 600 smtp-in6.nuvox.net.
tek-tips.com. 3600 IN MX 0 mail.tecumsehgroup.com.
tek-tips.com. 3600 IN MX 100 smtp-in1.nuvox.net.
tek-tips.com. 3600 IN MX 200 smtp-in2.nuvox.net.

;; AUTHORITY SECTION:
tek-tips.com. 3600 IN NS ns.shutter.net.
tek-tips.com. 3600 IN NS ns2.shutter.net.

If we look at the primary mail server mail.tecumsehgroup.com we can see if there is a reverse DNS entry;

; <<>> DiG 9.2.1 <<>> -x 216.45.19.20
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50934
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1

;; QUESTION SECTION:
;20.19.45.216.in-addr.arpa. IN PTR

;; ANSWER SECTION:
20.19.45.216.in-addr.arpa. 86400 IN PTR mail.tecumsehgroup.com.

;; AUTHORITY SECTION:
19.45.216.in-addr.arpa. 86400 IN NS ns.shutter.net.
19.45.216.in-addr.arpa. 86400 IN NS ns3.shutter.net.

So we can see that there is a PTR for this and that the reverse zone is delegated to ns and ns2.shutter.net as well. However, remember that the servers that hold the domain name do NOT have to also be authoratative for the reverve as well.

Also, there should only be one PTR per IP address so if multiple hosts are pointed at the same IP address, the PTR should be set up for just one of those hosts.

Chris.

**********************
Chris A.C, CCNA, CCSA
**********************