Reverse Lookups on shared server

I have a number of sites on a shared server in america, and none of them seem to be able to do reverse dns lookups on that server. Things like webserver logs and suchlike which usually give you a hostname and ip address only have the ip address listed.



I'm guessing there is some sort of software that needs to be installed/enabled on the server. If so, can I install it without root access?



I have a good relationship with the provider but I'd rather not have to bother them if I can help it.

Well let's rule out at least one possibility. I'm thinking that the dns server(s) you use for resolvers in /etc/resolv.conf can do reverse lookups just fine. So show me the results for this command to start this test:



cat /etc/resolv.conf

nameserver 127.0.0.1

nameserver 64.71.141.80

nameserver 216.218.200.200

Alright, let's see the results for these 3 commands:



dig @127.0.0.1 -x 216.117.186.93

dig @64.71.141.80 -x 216.117.186.93

dig @216.218.200.200 -x 216.117.186.93

; <<>> DiG 9.2.2-P3 <<>> @127.0.0.1 -x 216.117.186.93

;; global options: printcmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25774

;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 3



;; QUESTION SECTION:

;93.186.117.216.in-addr.arpa. IN PTR



;; ANSWER SECTION:

93.186.117.216.in-addr.arpa. 86400 IN PTR mail.dollardns.net.



;; AUTHORITY SECTION:

186.117.216.in-addr.arpa. 86400 IN NS ns2.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns0.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns1.aitcom.net.



;; ADDITIONAL SECTION:

ns0.aitcom.net. 169204 IN A 208.234.1.34

ns1.aitcom.net. 169204 IN A 216.117.186.139

ns2.aitcom.net. 169204 IN A 208.234.1.36



;; Query time: 95 msec

;; SERVER: 127.0.0.1#53(127.0.0.1)

;; WHEN: Fri Nov 26 18:57:49 2004

;; MSG SIZE rcvd: 186











; <<>> DiG 9.2.2-P3 <<>> @64.71.141.80 -x 216.117.186.93

;; global options: printcmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40661

;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 3



;; QUESTION SECTION:

;93.186.117.216.in-addr.arpa. IN PTR



;; ANSWER SECTION:

93.186.117.216.in-addr.arpa. 86400 IN PTR mail.dollardns.net.



;; AUTHORITY SECTION:

186.117.216.in-addr.arpa. 86400 IN NS ns1.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns2.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns0.aitcom.net.



;; ADDITIONAL SECTION:

ns0.aitcom.net. 13462 IN A 208.234.1.34

ns1.aitcom.net. 13462 IN A 216.117.186.139

ns2.aitcom.net. 13462 IN A 208.234.1.36



;; Query time: 117 msec

;; SERVER: 64.71.141.80#53(64.71.141.80)

;; WHEN: Fri Nov 26 18:57:49 2004

;; MSG SIZE rcvd: 186











; <<>> DiG 9.2.2-P3 <<>> @216.218.200.200 -x 216.117.186.93

;; global options: printcmd

;; Got answer:

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1559

;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 3



;; QUESTION SECTION:

;93.186.117.216.in-addr.arpa. IN PTR



;; ANSWER SECTION:

93.186.117.216.in-addr.arpa. 86400 IN PTR mail.dollardns.net.



;; AUTHORITY SECTION:

186.117.216.in-addr.arpa. 86400 IN NS ns2.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns0.aitcom.net.

186.117.216.in-addr.arpa. 86400 IN NS ns1.aitcom.net.



;; ADDITIONAL SECTION:

ns0.aitcom.net. 172140 IN A 208.234.1.34

ns1.aitcom.net. 172140 IN A 216.117.186.139

ns2.aitcom.net. 172140 IN A 208.234.1.36



;; Query time: 166 msec

;; SERVER: 216.218.200.200#53(216.218.200.200)

;; WHEN: Fri Nov 26 18:57:50 2004

;; MSG SIZE rcvd: 186

Now for the final test.



traceroute 216.117.186.93



traceroute uses the system to resolve IPs to domains. So this is a proof that IP resolution works fine not only on all 3 resolver servers, but also by the system that makes use of them.

1 gsr12008.fmt.ultraservers.net (64.62.137.1) 0.386 ms 0.316 ms 0.168 ms

2 gsr12012.fmt.he.net (64.71.131.173) 0.199 ms 0.498 ms 0.482 ms

3 pos2-1.gsr12416.pao.he.net (64.62.249.122) 194.951 ms 76.082 ms 3.947 ms

4 peer-01.palo.twtelecom.net (198.32.176.111) 1.940 ms 1.948 ms 1.980 ms

5 66.192.250.45 (66.192.250.45) 3.483 ms 3.575 ms 3.469 ms

6 core-02-so-1-0-0-0.chrl.twtelecom.net (66.192.255.22) 76.512 ms 75.991 ms 76.461 ms

7 66.192.242.23 (66.192.242.23) 77.982 ms 78.537 ms 78.442 ms

8 66.192.242.4 (66.192.242.4) 78.426 ms 78.035 ms 78.456 ms

9 66.192.242.41 (66.192.242.41) 78.472 ms 78.650 ms 78.468 ms

10 64-132-140-162.gen.twtelecom.net (64.132.140.162) 87.162 ms 89.439 ms 88.403 ms

11 mail.dollardns.net (216.117.186.93) 89.443 ms 92.391 ms 89.881 ms



So I guess that means it works? So why does the following code:



<?php

$hostname = gethostbyaddr($_SERVER['REMOTE_ADDR']);

echo $hostname;

?>



lifted straight from the php manual just return "217.64.123.69" instead of the hostname?

Dunno, perhaps it's a misconfiguration in PHP? I've written a little program for you that utilizes gethostbyaddr so that you can test to be 100% sure it's not the system's fault.



The attached tar/gz (not a zip) is both gethostbyaddr program and C code. It's written in such a way that should be convenient if you need a script to get the hostname for an IP.

Wow, thanks for that. I have run it as follows:



Pre...

<?php

echo `./gethostbyaddr 216.239.57.99`;

?>

...Post



(As I have no shell access, this is as good as it gets for me)



and the output I get is:



Pre...

...Post



Have I misunderstood? I have chmodded it to give world executable status

I take it that it works fine when executed directly? Have PHP check the return code of the program (system function is one way to test this). The return code is 0 if it was successful and it returns the hostname. Otherwise you get an error code of 1, 2, or 3 and there's no output.