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| SL Da... |
 Posted: Tue Sep 22, 2009 3:31 pm |
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1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
Thanks. |
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| David Schwartz... |
| Posted: Tue Sep 22, 2009 4:15 pm |
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Guest
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On Sep 22, 6:31 pm, SL Da <sb5... at (no spam) yahoo.com> wrote:
Quote: 1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
Why are you confused? It would help if you explained what you found
confusing about this. Forward and reverse namings are completely
independent. The two questions follow completely different paths, and
if they provide corresponding answers, it's only because someone
carefully set them up that way.
DS |
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| SL Da... |
| Posted: Tue Sep 22, 2009 5:23 pm |
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I don't have much knowledge in this area.
When I create a domain on a web server, there is no problem. I suppose
all entries are done automaticaly by the ISP's software.
But then suddenly there are problems (someone else's domain). First
the domain cannot be reached, now the reverse DNS does not work. I
think someone has tempered the DNS record, or removed the domain
account form the server (I guess).
Quote: Why are you confused? It would help if you explained what you found
confusing about this. Forward and reverse namings are completely
independent. The two questions follow completely different paths, and
if they provide corresponding answers, it's only because someone
carefully set them up that way.
DS |
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| David Schwartz... |
| Posted: Tue Sep 22, 2009 6:00 pm |
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Guest
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On Sep 22, 8:23 pm, SL Da <sb5... at (no spam) yahoo.com> wrote:
Quote: I don't have much knowledge in this area.
When I create a domain on a web server, there is no problem. I suppose
all entries are done automaticaly by the ISP's software.
Some hosting companies may do this if you host the domain locally. But
they are doing two logically independent things based on a single
trigger.
Quote: But then suddenly there are problems (someone else's domain). First
the domain cannot be reached, now the reverse DNS does not work. I
think someone has tempered the DNS record, or removed the domain
account form the server (I guess).
There's no way to tell without troubleshooting. But that reverse DNS
doesn't work doesn't tell you anything, since it's not required.
DNS is not bidirectional. An entry that maps www.example.com to
1.2.3.4 is part of the zone for "example.com" and managed by whoever
or whatever managed "example.com". An entry that maps 1.2.3.4 to
www.example.com is part of the zone for 3.2.1.in-addr.arpa and managed
by whoever or whatever manages that block of IP addresses.
There is, in general, no way to find what names map to a particular IP
address or all the IP addresses that reverse to a particular name.
Each entry goes only one way.
DS |
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| Wanna-Be Sys Admin... |
| Posted: Tue Sep 22, 2009 8:01 pm |
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Guest
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SL Da wrote:
Quote: 1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
Thanks.
You probably get a failure (can't find) "87.33.160.209.in-addr.arpa",
which means you don't have reverse DNS set up. If you are
authoritative, you can add a PTR record to the DNS. Otherwise ask your
provider to do it, if you need rDNS for any reason. You can also run
"host ip.address.here" for a shorter response, too. You can also add
the domain and IP locally to your hosts file.
--
Not really a wanna-be, but I don't know everything. |
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| Chris Cox... |
| Posted: Tue Sep 22, 2009 10:10 pm |
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Guest
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SL Da wrote:
Quote: 1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
1. Assuming the ping looked up bayregatta.com via DNS, that's a DNS A record lookup.
2. Since that is going to use the defined DNS, it's trying to find the PTR record associated by the IP. Specifically it is trying to lookup
87.33.160.209.in-addr.arpa. But apparently there is no zone for the PTR record, thus the message. |
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| SL Da... |
| Posted: Wed Sep 23, 2009 12:38 am |
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Guest
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I maintained some web pages for a company a little while ago.
Recently someone called me up, saying they cannot accessed its control
panel. I understand that an IT guy has left the company not long ago,
with a little grudge may be.
I discovered I cannot ping the site (server failed); looked like a DNS
error. It was restored a week later (not by me), but then the reverse
DNS does not work.
Quote: What do you mean someone else's domain and there being a problem? Which
domain can't be reached? BTW, a domain not being responsive has
nothing to do with the reverse DNS, so I assume you got a different
error when running nsloopkup? Does it work at all? Perhaps there is an
issue when one or the other name servers don't respond or something?
Exactly what is the issue you're having?
--
Not really a wanna-be, but I don't know everything. |
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| Wanna-Be Sys Admin... |
| Posted: Wed Sep 23, 2009 1:39 am |
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Guest
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SL Da wrote:
Quote: I don't have much knowledge in this area.
When I create a domain on a web server, there is no problem. I suppose
all entries are done automaticaly by the ISP's software.
How do you mean? What is the issue you have?
Quote: But then suddenly there are problems (someone else's domain). First
the domain cannot be reached, now the reverse DNS does not work. I
think someone has tempered the DNS record, or removed the domain
account form the server (I guess).
What do you mean someone else's domain and there being a problem? Which
domain can't be reached? BTW, a domain not being responsive has
nothing to do with the reverse DNS, so I assume you got a different
error when running nsloopkup? Does it work at all? Perhaps there is an
issue when one or the other name servers don't respond or something?
Exactly what is the issue you're having?
--
Not really a wanna-be, but I don't know everything. |
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| N. Bazan... |
| Posted: Sat Oct 03, 2009 10:46 pm |
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Guest
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On Sep 23, 3:31 am, SL Da <sb5... at (no spam) yahoo.com> wrote:
Quote: 1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
Thanks.
When you ping bayregatta.com your get an A record back. A record
contains 209.160.33.87
When you do nslookup 209.160.33.87 you perform something like reverse
lookup for domain 209.160.33.87. There are no such domain and there
are no ptr record for this ip.
PTR records looks like this 209-160-33-87.your-isp.com and commonly
maintained by isp`s.
You do not need any ptr records for the website. But you have
mail.bayregatta.com at same ip without ptr records. You must have one
ptr for your mail server, otherwise your mail server ip can be
blacklisted.
Try to use some swiches such as nslookup -type=ptr(ns,soa,mx)
209.160.33.87. You can also find your full DNS report at
http://www.magic-net.nl/dns-lookup.php or check your PTR direct
http://www.magic-net.nl/dns-and-ip-tools.php?ptr=209.160.33.87&do=Find |
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| N. Bazan... |
| Posted: Sat Oct 03, 2009 10:58 pm |
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Guest
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On Sep 23, 12:38 pm, SL Da <sb5... at (no spam) yahoo.com> wrote:
Quote: I maintained some web pages for a company a little while ago.
Recently someone called me up, saying they cannot accessed its control
panel. I understand that an IT guy has left the company not long ago,
with a little grudge may be.
I discovered I cannot ping the site (server failed); looked like a DNS
error. It was restored a week later (not by me), but then the reverse
DNS does not work.
What do you mean someone else's domain and there being a problem? Which
domain can't be reached? BTW, a domain not being responsive has
nothing to do with the reverse DNS, so I assume you got a different
error when running nsloopkup? Does it work at all? Perhaps there is an
issue when one or the other name servers don't respond or something?
Exactly what is the issue you're having?
--
Not really a wanna-be, but I don't know everything.
Ping uses ICMP protocol that can be blocked by your firewall. ICMP is
not necessary for the web-site. But you must have A record for your
website that points to your ip, and one A record for your
cpanel.website.com that points to same or different ip. Your web
server must accept headers www.website.com and cpanel.website.com. |
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| David Schwartz... |
| Posted: Sun Oct 04, 2009 6:57 pm |
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Guest
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On Oct 4, 1:58 am, "N. Bazan" <nikba... at (no spam) gmail.com> wrote:
Quote: Ping uses ICMP protocol that can be blocked by your firewall. ICMP is
not necessary for the web-site.
This is not true. ICMP is *required*, it is not optional. Blocking
ICMP 'fragmentation required' packets can break path MTU discovery.
DS |
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| Wayne... |
| Posted: Tue Oct 06, 2009 11:17 pm |
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Guest
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SL Da wrote:
Quote: 1. When I ping 'bayregatta.com' I see 209.160.33.87
2. When I try 'nslookup 209.160.33.87', I get 'non-existent domain'.
I am a bit confused. Can someone explain ?
Thanks.
The answer is simple: "ping" uses the resolver to lookup
the name or number. "nslookup" bypasses the resolver
and uses DNS directly. The name may be listed in your
/etc/hosts file, or (as others have explained) the DNS
A record for bayregatta.com may be present without
the matching PTR record. Either reason would explain
the symptoms you describe.
[OT]
A useful but little known tool is "getent", which
uses the nsswitch and resolver to look stuff up:
$ getent hosts bayregatta.com
209.160.33.87 bayregatta.com
$ getent hosts 209.160.33.87
209.160.33.87 bayregatta.com
So if the lookup works with (say) nslookup but not
getent, your resolver configuration is probably wrong.
If it works with getent but not nslookup, the data may
not be in DNS at all (or, more likely in your case,
the PTR record may be wrong or missing).
Note other lookup tools also bypass the resolver,
such as "host" and "dig".
--
Wayne |
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